By Wei Yang|April 30, 2015
Adding lime in the fall to soil in your blueberry fields helps to maintain a desired soil pH range. (Photo credit: Wei Yang)
Blueberry fields with pH ranges out of the optimum (4.2-5.5) are common in many areas of blueberry production. I know you all feel confident about applying elemental sulfur to reduce soil pH to the desired range, but what should you do if your soil pH drops below 4.5, and how that will affect blueberry plant growth?
Let’s first understand why soil pH keeps decreasing every season with fertilization in blueberry fields. We all know blueberries prefer ammonium-based fertilizer — among the largest percentage of cations taken up — as their nitrogen source,. This actually is the primary reason your soil pH keeps decreasing every season.
During the uptake of ammonium ions, blueberry plant roots excrete hydrogen ions, which accumulate in the soil to increase soil acidity. When urea is used, it will first break down to ammonium and carbonate by urease. This process takes one hydrogen ion away from the soil, so urea is less acidifying than ammonium sulfate fertilizer.
Then, ammonium may form ammonia (NH3), so soil pH close to the urea particles could increase temporarily. Because of the eventual uptake of ammonium by blueberry plants, the long-term effect of urea on soil pH will still be a reduction in soil pH.
Just Add Lime
What can you do to reduce the rate of soil pH drop in blueberry production? We can calculate the liming factor (or acidifying potential) of different fertilizers and add lime to neutralize it.
Unfortunately, the acidifying potential of these various nitrogen fertilizers is calculated based mostly on their nitrification in the soil and because blueberry plants take up most of the nitrogen fertilizer in the ammonium form, this traditional way of determining lime requirement may be of limited use for blueberries.
Since the majority of soil acidity in blueberry production is mainly due to root exudation of hydrogen ions into the soil by removal of cations, such as ammonium ion, calcium, magnesium, and potassium from the soil under low soil pH conditions, the soil acidification or the amount of lime required can be estimated by the ratio of base cation to nitrogen in plant tissues.
I estimated this ratio for blueberry plants is around 0.7-1.0. So take the high number of the ratio, for one acre of blueberries with a 20,000 lb. yield, about 170 lbs. of lime is needed to neutralize the soil acidification potential due to fertilizer uptake. This means it’s safe to apply about 150 to 200 lbs. of lime every fall before the next spring to stabilize your soil pH.
Apply In Autumn
The best time to apply lime is in fall or when winter starts. Also, the amount of lime mentioned so far is for band applications within the planting row. It is not the broadcast application rate. Remember, do not over-lime and do not add lime in the spring when applying fertilizers.
I know liming blueberry fields sounds really strange because blueberry plants love acid soils and are calcifuge (do not tolerate alkaline soil) plants. However, the benefits of adding some lime in the fall (not in the spring) to maintain a desired soil pH range have been practiced in Oregon’s Willamette Valley by some growers. The calcifuge nature of the blueberry plant really means its inability to survive in high pH soils and has nothing to do with lots of calcium in the soil.
If the soil pH in your blueberry field drops below 4.5 already, especially in upland or mineral soils, free soil aluminum could interfere with nitrogen, phosphorus and iron uptake, which leads to iron chlorosis. You can do two things to relieve this problem.
First, you will need to start bringing the soil pH up gradually. This could be a long process since lime moves into the soil profile slowly when surface applied. You can add 200 lbs. lime/acre in addition to the lime you need to neutralize the potential acidity produced by fertilizer uptake during the growing season. You can do this for a few seasons, and then wait a few more years to test the soil pH to see if more lime is needed.
Second, you can find ways to reduce the concentrations of free soil aluminum in the soil. Increasing soil organic matter such as sawdust mulch, compost material, and/or organic acids will reduce free soil aluminum concentrations over time.
Finally, I’d like to mention the difference between sulfur (S) and sulfate (SO4=) on soil acidity. There is a misconception about sulfate that it reduces soil pH. The reality is sulfate does not reduce soil pH.
When potassium sulfate or ammonium sulfate are applied as potassium or nitrogen fertilizer, the sulfate group in both fertilizers will either be taken up by the plants or lost to leaching, a process which does little to change soil pH.
When elemental sulfur is applied to the soil, however, it will be oxidized by sulfur oxidizers (bacteria) such as Thiobacillus species or other heterotrophic sulfur oxidizing fungus such as Aspergillus niger and Trichoderma harzianum. During this oxidation process, sulfuric acid is produced and soil pH is lowered. Interestingly enough, the rate of elemental sulfur oxidation increases with soil pH. This is because soil bacteria are more active at higher soil pH.
In summary, the reason for the gradual soil acidification in blueberry production is due to the action of blueberry roots, not the nitrification processes that happen in soil as usually assumed because the nitrification process is limited at low pH soils.
Wei Yang is an associate professor in the Department of Horticulture at Oregon State University and a berry crops Extension agent at the North Willamette Research and Extension Center in Aurora, OR. See all author stories here.
- Overapplied Sulfur for blueberries
- Soil Prep For Blueberry Plant: Lower Soil pH For Blueberries
- Testing Blueberry pH Soil Level
- New Blueberry Plantings – Soil Prep for Blueberry Plant
- Existing Blueberries – Lowering Blueberry Soil pH
- Soil test before you plant blueberries
- Reducing Soil pH
- Sulfur for Blueberries
Overapplied Sulfur for blueberries
Most people tend to be afraid of elemental sulfur, but they shouldn’t be. It is one of
the best methods of acidifying the soil, yet it is surprisingly gentle
and is usually considered to be an organic gardening practice. I buy it
in 20 pound bags on Amazon.
Yes, you should use pine mulch,
compost and similar things, when available. You should also try to
amend you soil to try to get a sandy loam. However, once you have done
all of that, you probably will STILL need to acidify the soil more. But also keep in mind that your soil will CONSTANTLY be trying to gradually revert to its normal pH.
like a pH of 4.0 to 5.5 or so. This is definitely an acidic soil level and
is very close to the acid level of apple cider vinegar. Meanwhile, most
people have neutral soil, in the range of 7.0 to 7.5, and, if you live
near mountains/hills or lakes/rivers that contain limestone, your pH for
both soil and water will probably run in the range of 8.0 to 8.4.
Blueberries might possibly barely survive, but will never do well in
such soil. So, you must acidify it.
ONE POUND of yellow,
elemental sulfur powder mixed into the surface inches of 100 square
feet, will drop the pH by 1.0 points over a period of about a 1 year.
It works because the action of soil bacteria, along with moisture and
warm temperatures, allows the soil bacteria to gradually convert the
elemental sulfur to sulfuric acid, and this acid is never really free,
but it neutralizes the limestone and alkaline components. So, 4 pounds
of sulfur in an area of 10 x 10 will often drop the pH from 8.0 to 4.0
in a year or so. But the soil, and water, will push back, especially if
the soil is derived from a moderate amount of limestone. The limestone
contained in the soil continues to dissolve and will work to bring the
pH right back up. Around here, we need to use 5 to 10 pounds of
elemental sulfur in such an area, in order to get the pH down to an
In addition to the above mixture of sulfur with
surface soil, if you soil is on the alkaline side, like ours, mix TWO
whole cups (1 pound) of sulfur with the dirt in the planting hole, at
the same time as you plant the blueberries.
Please note that
these instructions are for using ELEMENTAL SULFUR, which is generally a
bright yellow powder, AND, it takes time to work (a year or more), AND
you need to keep reapplying sulfur to the top of the soil at a rate of
1/2 pound to 1 pound per 100 square feet, every year or two. I
also went online and bought some simple electronic pH testers for around
$20 or $25 dollars each. When I want to test my soil, I mix some soil
with DISTILLED water (available at most grocery stores) and use the
tester on the resultant runny mud mixture.
Soil Prep For Blueberry Plant: Lower Soil pH For Blueberries
Many times, if a blueberry bush is not doing well in a home garden, it is the soil that is to blame. If the blueberry soil pH is too high, the blueberry bush will not grow well. Taking steps to test your blueberry pH soil level and, if it is too high, lowering blueberry soil pH will make a huge difference in how well you blueberries grow. Keep reading to learn about proper soil prep for blueberry plants and how you can lower soil pH for blueberries.
Testing Blueberry pH Soil Level
Regardless of whether you are planting a new blueberry bush or trying to improve the performance of established blueberry bushes, it is essential that you have your soil tested. In all but a few places, your blueberry soil pH will be too high and testing the soil can tell how high the pH is. Soil testing will allow you to see how much work your soil will need in order to grow blueberries well.
The proper blueberry pH soil level is between 4 and 5. If your blueberry bush’s soil is higher than this, then you need to take steps to lower the soil pH for
New Blueberry Plantings – Soil Prep for Blueberry Plant
If your blueberry soil pH is too high, you need to lower it. The best way to do this is too add granular sulfur to the soil. About 1 pound of sulfur per fifty feet will lower the pH one point. This will need to be worked or tilled into the soil. If you can, add this to the soil three months before you plan on planting. This will allow the sulfur to better mix with the soil.
You can also use acid peat or used coffee grounds as an organic method of acidifying the soil. Work in 4-6 inches of peat or coffee ground into the soil.
Existing Blueberries – Lowering Blueberry Soil pH
No matter how well you do soil prep for a blueberry plant, if you do not live in an area where the soil is naturally acidic, you will find that the soil pH will return to its normal level in a few years if nothing is done to maintain the lower pH around the blueberries.
There are several methods you can use to either lower soil pH for blueberries that are established or to maintain the already adjusted blueberry pH soil level.
- One method is to add sphagnum peat around the base of the blueberry plant about once a year. Used coffee grounds can also be used.
- Another method for lowering blueberry soil pH is to make sure you are fertilizing your blueberries with an acidic fertilizer. Fertilizers containing ammonium nitrate, ammonium sulfate, or sulfur-coated urea are high acid fertilizers.
- Adding sulfur to the top of the soil is another way to lower soil pH for blueberries. It may take some time for this to work on established plantings because you will not be able to work it far into the soil without causing damage to the blueberry bush’s roots. But it will eventually work its way down to the roots.
- A quick fix for when the blueberry soil pH is too high is to use diluted vinegar. Use 2 tablespoons of vinegar per gallon of water and water the blueberry with this once a week or so. While this is a quick fix, it is not a long lasting one and should not be relied on as a long term way for lowering blueberry soil pH.
Planting & Caring for Blueberry Plants
NOW LISTEN UP! THIS IS WHAT DAD SAYS! — Before reading ANY of the following information, Dad wants me to mention one critical thing: Blueberries LOVE AN ACID SOIL between 4.5-5.5. If your pH isn’t in line with this – YOUR PLANTS WILL NOT THRIVE. Dad says that if you’re not going to bother to test your soil – don’t bother wasting your money buying plants! They may grow a little, but they will never thrive if the soil acidity isn’t right! He says that in the Chelan/Manson area, soils typically run around 6.5-7.0, depending on what the prior use of your land was. Test kits are easy to use and they’re cheap at your local hardware store. DO IT RIGHT, FOLKS!
Blueberry Hills Recommended Shopping List
Blueberry Plants: We recommend 2 per plants per blueberry obsessed family member
Peat Moss: figure 1 bale peat moss (4 cu. ft. bale) with do 4-5 blueberry plants
Mulch: About 1 cu. ft. per plant. We use chipped lawn debris from our local recycle center and LOVE it
Fertilizer: We recommend a rhododendron fertilizer
Soil Acidifier: We use Sulfur here at Blueberry Hills?
A Redneck’s Guide to
Planting & Caring for Blueberry Plants
This is Kari’s version. If you want to serious version…well — that’s down below. But it ain’t nearly as much fun.
Site Selection & Preparation
Select a sunny location in well-drained soil, free of weeds and well worked. (Another tried & true method of site selection is “anythin’ within the range of the TV remote without having to actually flail or hunker at an odd angle from yer lawn chair.” Ya’ loose points fer that.) Locate in an area where irrigation water is available, as best results will be obtained by keeping the root zone moist throughout the growing season. It’s been proven that even better results can be obtained by simply payin’ someone else to care ’bout em. Where the soil is poor or marginally drained, raised beds 3-4 feet wide and 8-12″ high work very well for blueberries. These beds can also be ideal for hosting a funeral at home. This is an economical solution, as well as the elderly in attendance will truly appreciate not having to hunker down to pay last respects. This’ll likely put’cha DI-rectly on top-a Aunt Martha’s Christmas list.
A fail-safe way to grow blueberries in almost any soil is to encourage your family & friends to plant ’em at their own stinkin’ house. Tell-em how easy they are to grow & make sure to go on-n-on ’bout how much money they’ll make. If that fails, you should incorporate peat moss into the planting medium. For planting directly in the ground, work up a planting area approximately 2-1/2 feet in diameter and one foot deep. Add peat moss to a bunch of the soil. Dig around & mix it up real good. Next, drag yer dog out’a yer fresh hole. Remember, this is YOUR hole. You fight fer’ it. It also might be good to lock him up so he doesn’t see YOU do sumpthin’ he got the boot’ fer doin’ last week. This tends to confuse. Note: If diggin’ is in his moral fiber and sumpthin’ he simply must do to be complete as a dog, encourage & reward him to do it in yer neighbor’s yard. 2 birds–1 stone.) Add an equal amount of pre-moistened peatmoss and mix well. One 4 cubic foot compressed bale will usually be sufficient for 4-5 plants. If ya don’t have that, your nosey, rich neighbors likely got it from “the WalMart”. Remember folks: “What’s theirs is yours!” It’s truly ideal to look for it late at night with a small flashlight. For raised beds, mix equal volumes peat moss with acid compost or planting mix. Again, those lousy-good-fer-nuthins next door likely got that too. Help yerselves. Blueberries thrive in acidic soils. If worse comes to worse, your local garden center representative can recommend a good soil acidifier & underarm deodorant if it’s the social season.
Blueberries can be planted as close as 2-1/2 feet apart to form solid hedgerows or spaced up to 6 feet apart and grown as individual specimens. If planted in rows, allow 8 to 10 feet between the rows depending on equipment used for mowing or cultivating. Note: Although it requires effort, its helpful to actually TAKE your personally selected lawn chair out to use fer good measure between rows.
For container stock, remove from pot and lightly roughen up the outside surface of the rootball. You can also save time & achieve the exact same effect by backin’ up real fast with your tailgate down & then stompin’ on the brake. (Important: Avoid doin’ this if yer on a date. It appears lazy.) Set the top soil line of the plant level to the existing ground and firm around rootball. Mound soil up along sides of exposed root mass. Water in well. Clean fingernails with pocket knife. Your job here is done.
Blueberries do best with a 2-4″ mulch over the roots to conserve moisture, prevent weeds and acid organic matter. Bark mulch, acid compost, sawdust, grass clippings, nail clippings, etc. all work well. Repeat every other year, although the toenail clipping should be more frequent.
It is important that blueberries get established before allowing them to bear fruit. Same with yer good fer nuthin’ kids. Thereafter, they should be heavily pruned each year to avoid over-fruiting which results in small fruit or poor growth as well as simply bein’ a financial burden on the system.
Remove all blooms, as they appear the first year. (We find that the “she loves me – she loves me not” method is effective and keeps ya’ focused.) In years thereafter, follow these steps after the leaves have dropped.
Remove low growth around the base. If it doesn’t grow UP, it gets pruned out! (Same goes fer those deadbeat kids!) Remove the dead wood, and non-vigorous twiggy wood. Select for bright-colored wood with long (at least 3 inch) laterals. Remove blotchy-colored short growth. Toss that over the fence into that lousy-good-fer-nuthins’ yard.
If 1/3 to 1/2 of the wood has not been removed by the above steps, thin out the fruiting laterals and small branches until this balance has been obtained.
Obtain & consume frosty beverage while admiring the fruit of your efforts from lawn chair of choice.
Blueberries like acid fertilizers such as Rhododendron or Azalea formulations. For newly planted stock, use 2 tablespoons of 10-20-10 in late spring or once plants are established. (Careful! Blueberries are very sensitive to over fertilization!) For subsequent years, use 1 ounce of fertilizer for each year from planting to a total of 8 ounces per plant. If that doesn’t sound right, well…jest dump some on there. Apply in early spring and again in late spring for best results. Always water well after fertilizing and don’t forget that frosty beverage. Remember not to fertilize after the 4th of July as your bushes need time to go dormant before fall.
For organic fertilizers, blood meal and cottonseed meal work well. Avoid using fresh manure. It’ll burn the plants and it simply smells, well…like fresh manure. Note: Fresh manure is always the fertilizer of choice if plants located in your neighbors’ yard.
Checklist of “Stuff I Hope My Lousy Neighbors Got at The WalMart”
Blueberry Plants (at least 2 per family member)
Peat Moss (4-5 plants per bale)
Mulch (1 cu. ft. per plant)
THE ANNUAL PLANNER
For them-thet’r thinkin’ “Yup. I picked ’em. My work here is done.” Wake up & smell the Folgers, folks. It ain’t over.
November to mid-March
Apply fall herbicides, November to December
Locate & use toenail clippers for first time all winter
Apply pre-emergent herbicides before weed growth starts, late February to mid-March
Remove diseased and winter-injured tissue. Toss over neighbor’s fence. Remember: “It’s good to recycle.”
Leaf and flower bud break : Late March to late April
Make first fertilizer application
Control weeds by cultivation and/or herbicides
Purchase upgraded lawn chair with smooth action, (make sure to check) insulated cup holder & good spot for your remote.
Bloom period : Late April to late May
Introduce bees for pollination
Make second fertilizer application late May to early June
It’s Spring! Let the ladies know yer lookin’ & be aggressive!
Position & straddle lawn chair in front yard. (Extra points for binoculars.)
Say “Yes” to the T-shirt with yellow pit stains, socks ‘n sandals & plaid boxer shorts that hang open freely. It’s important to show a sense of style.
It’s also important to present a well groomed appearance. Wax yer back. Clip stray nose, ear & out of control eyebrow hair. Don’t just slick it all up & wrap it around yer head like ya did last year. Chicks hate that stuff.
Fruit development : June and July
Cultivate for weed control in row middles. Make sure lawn chair still fits.
Make third fertilizer application, early to mid-July, if needed
Irrigate as neededdamage control devices. Shotguns are ideal & also work well for supporting neighborly relations (again…2 birds-1 stone)
Collect plant tissue nutritional analyses late July. Wonder “what the heck that was for?!” about 3 months later & toss over neighbor’s fence.
Harvest : July to September
Harvest and market fruit. Irrigate as needed. Flaunt your giant, fresh berries in front of those lazy good-fer-nuthins’ that refused to grow your berries. Be truly obnoxious. Reflect on your behavior while you scratch yourself openly. Apologize for your rude behavior & offer them a fistful of your bounty.
Postharvest growth : September to mid-October
?Cultivate to control weeds
Irrigate as needed
Renew subscription to “Women ‘n Ammo”; it’s gonna’ be a long winter.
🙂 Blueberry Kari
The Serious, Boring Version…
How to Plant & Care for Blueberry Plants
…according to Oregon State University’s Website
Growing blueberries can be very rewarding. You can eat the berries fresh, make them into pies and other desserts, or freeze, dry, or can them for later use. In Oregon, the blueberry fruiting season depending on the type of blueberry and cultivar. The fruit on each cultivar ripens over a 2? to 5?week period. The most common type of blueberry grown in Oregon is the northern highbush blueberry. Other types of blueberries include southern highbush, rabbit eye, lowbush, and half?high. Highbush blueberries are perennial, long?lived (40 to 50 years), deciduous shrubs with a mature height of 5 to 9 feet. Attractive as ornamentals, they progress from a profusion of white or pink blossoms in spring to colorful foliage (fall) and wood (winter). You can grow plants in beds, rows, hedges, or individually. Dwarf and semi?dwarf cultivars (varieties) are available for growing in containers.
Selecting a site
Blueberries require a sunny location for full production. Avoid areas surrounded by trees. Trees can provide too much shade, compete with plants for water and nutrients, encourage birds, and interfere with air movement around the plants. Poor air circulation favors the development of diseases.
Blueberries have very specific soil requirements. Plants grow best in well?drained, light, sandy loam soils that are high in organic matter and have a pH between 4.5 and 5.5. Avoid planting on heavy soils that drain slowly. Water standing on the soil surface for more than 2 days during the growing season can damage roots. The soil water table should be at least 14 inches below the soil surface, or roots will suffocate. If your garden has only coarse, sandy or gravelly soils, pay careful attention to watering and fertilizing. You can modify many soils that are initially unsuitable to make them suitable for blueberry production (see “Preparing the soil?).
Growing Blueberries in Your Home Garden
It’s a good idea to plant more than one cultivar. Although most northern highbush blueberry cultivars are self?fertile, cross?pollination produces larger berries. Also, if you plant two or more cultivars that ripen at different times, you’ll lengthen the harvest season. To ensure adequate cross pollination, plant more than one cultivar within each type of blueberry you select. Within each type, cultivars have sufficient overlap in the bloom period for adequate cross pollination.
Preparing the soil
Blueberries require an acid soil, relatively high organic matter content, and good drainage. If your soil is not naturally suitable for blueberry plant growth, you’ll need to modify it before planting. Blueberry plants are long?lived, so considerable time and expense in preparing the soil can be justified. If you plan on growing several plants, it’s better to group them in a bed or row than to scatter them around your garden. You’ll obtain better results if you prepare an entire bed, rather than digging holes for individual plants and preparing soil to fill the holes. Be sure to eliminate all perennial weeds before planting.
Soil pH adjustment
An acid soil with a pH between 4.5 and 5.5 is considered ideal for highbush blueberries. Poor blueberry plant growth resulting from soil pH that is too high is the most common problem when growing blueberries in the home garden. In this situation, plants often have yellow leaves with green veins. These symptoms are most likely on younger leaves. For most soils, the pH must be lowered (made more acidic). Test soil pH a year before planting because acidification, if necessary, takes more than 6 months. (For more information about soil testing, see Laboratories Serving Oregon: Soil, Water, Plant Tissue, and Feed Analysis, and Soil Sampling for Home Gardens and Small AcreagesIf the pH is between 5.7 and 6.5, acidify the soil by adding finely ground elemental sulfur (S) to the soil before planting. The amount of S needed depends on how much the soil pH needs to be lowered and the soil type.
• To lower the pH from 6.5 to 5.4 in a clay loam soil, apply 3.5 to 4.5 lb S/100 sq ft.
• To lower the pH from 6.1 to 5.4 in a clay loam soil, apply 2 to 2.75 lb S/100 sq ft.
• Heavier soils may require more S for a similar amount of acidification.
It’s best to use the lower rate initially, check soil pH again in 6 months to a year, and apply more S only if necessary. Do not apply more than 7 lb S per 100 sq ft at one time. If the pH is between 5.5 and 5.7, mix in Douglas-fir sawdust and ammonium sulfate fertilizer before planting. These materials will acidify the soil. Yellow foliage caused by high-pH soil. 3 If the pH of an organic soil is higher than 6.5, it’s usually not practical to acidify it enough for growing blueberries. In some cases, soil pH is too low for blueberry production. If the pH of your soil is below 4.0, incorporate finely ground dolomitic limestone at a rate of about 5 to 10 lb/100 sq ft. Incorporating organic matter Before planting, incorporate organic matter, such as Douglas-fir sawdust or bark, to improve soil aeration and drainage. Yard debris compost may be used, but it often has a high pH (above 7.0, compared to pH 4.0 to 4.5 of Douglas-fir sawdust) and can be high in salts. Spread sawdust over the row to a width of about 3 feet and a depth of 3.5 inches. To aid in decomposition of the sawdust, add 2 lb nitrogen/100 feet of row length (10 lb ammonium sulfate, 21?0?0). Incorporate the sawdust and fertilizer with a rototiller. Improving drainage Although blueberries require readily available moisture, they will not tolerate poor drainage. Ideal soils are well drained with a water table 14 to 22 inches below the surface. You often can make poorly drained soils suitable for blueberries by tiling and/or planting on raised beds. A raised bed 12 to 18 inches high and 3 feet wide usually is sufficient to provide adequate drainage and aeration. Raised beds can be constructed with wood walls, but walls are not necessary if you can form a raised bed (using natural soil and incorporated sawdust) by hilling.
Growing blueberries in containers
You also can grow blueberries in containers. Northern highbush blueberries require a large container such as a wine barrel. Half?high types can be planted in a 10?gallon or larger container. A good planting mix consists of about 80 percent fir bark, 10 percent peat moss, and 10 percent perlite.
Establishing your planting
Plant healthy 2?year?old plants in October or from March through April. Purchase container?grown plants from a reputable nursery. Space plants 4 to 5 feet apart in the row. Spacing between the rows can be 8 to 10 feet. Set plants no more than ¾ inch deeper than they were growing in the nursery row or container. Planting too deep can smother plants. Firm the soil well to remove air pockets. Do not fertilize plants when you plant them. Water thoroughly after planting, but don’t over water. Prune all branches back by about 30 to 40 percent by removing older wood and keeping nice new whips (new growth at base of plant); this encourages vigorous new growth. Remove blossoms Prune off flower buds at planting. Do not allow plants to produce fruit the first season. Be patient! It’s important that plants grow well the first year, and flower and fruit production hinders growth. Fruit buds are “fat buds on the tip of last year’s growth; vegetative or shoot buds are barely visible on the lower portion of the shoot. Young plants require little pruning for the first 2 or 3 years compared to mature plants, but it is important to limit fruit production the first 2 years. You will have to remove weak portions of the plant and limit the number of fruit buds to ensure that plants grow well.
Keep at least a 4?foot area around the plants free of weeds during the growing season. Blueberry roots grow mostly near the soil surface. Thus, to prevent root damage, cultivation must be very shallow and not too close to the plant.
Blueberries grow better when mulched. Mulching keeps the soil cool, conserves moisture, adds organic matter to the soil, improves soil structure, and aids in weed control. After planting, apply a mulch of Douglas fir sawdust or bark to a depth of 2 to 3 inches. Increase the depth of the mulch to 6 inches over a period of years. You can mulch the entire soil surface (you’ll no longer have to cultivate), or you can place a 3? to 4?foot?wide band of mulch in the row. You may have to apply 25 percent more nitrogen fertilizer on mulched plantings compared to unmulched plantings, depending on how fresh the sawdust is. Fresh sawdust “ties up? nitrogen while it decomposes, so you need to add more for the plants.
In late April of the planting year, apply 0.2 oz of nitrogen (N) per plant (equivalent to 1 oz of ammonium sulfate fertilizer, 21?0?0, or 0.4 oz urea, 46?0?0). Add the same amount of N fertilizer in early June and in late July. Sprinkle the fertilizer evenly within 12 to 18 inches of each plant, but not directly on the crown or stems. Ammonium sulfate and urea fertilizers contain no phosphorus (P) or potassium (K). In general, home garden soils have sufficient P and K. However, if soil or plant?tissue analysis shows a deficiency of either P or K, apply a more complete fertilizer. Use mixtures that contain potassium sulfate rather than potassium chloride; blueberries are very sensitive to chloride. Also, make sure the N is in the form of ammonium, not nitrate; blueberries do not take up nitrate N.
Blueberries have a shallow, fibrous root system, so they’re susceptible to drought injury. A uniform and adequate supply of water is essential for optimum growth. On average, young plants need about 1 inch of water per week. If this amount isn’t supplied by natural soil water or rain?fall, you must irrigate. Check the soil frequently for adequate moisture and irrigate if necessary.
Checklist for establishing a blueberry planting and taking care of plants the first year
• Select a good site.
• Eliminate all perennial weeds before you plant and before they go to seed.
• Test the soil pH a year before planting.
• Prepare the soil the year before planting:
— Incorporate organic matter.
— Modify soil pH if necessary.
— If the site drains poorly, use tile drains and/or build raised beds.
• Choose cultivars—planting two or more leads to larger fruit and a longer harvest period.
• Plant in the fall or spring.
• Apply 2 to 3 inches of sawdust or other mulch.
• Prune all branches back by 30 to 40 percent.
• Apply fertilizer in late April after planting.
• Keep the planting weed-free.
• Irrigate as needed.5
Care of established plants
Add mulch as required to maintain a depth of about 6 inches once plants are mature. In row plantings, widen the mulched area to at least 4 feet as plants become larger. As a rule, sawdust mulch decomposes at the rate of about 1 inch per year.
In the second year, apply 0.25 oz of N per plant (1.2 oz of 21?0?0 or 0.55 oz 46?0?0) in April, May, and June. The total amount of N applied per plant will be 0.75 oz. Spread fertilizer evenly around the plant, over an area approximately equal to the spread of the bush. Try not to apply fertilizer to the base of the canes. In year 3, increase the total fertilizer N applied to 0.8 oz. Divide the total into three equal portions and apply one?third each in April (around bloom time), May, and June. In year 4, increase to 1 oz per plant. As the planting ages, slowly increase the total N applied to a maximum of 2.5 oz N per plant (12 oz of 21?0?0) in mulched plantings. Continue to split the total into three applications in April, May, and June. In general, you should not fertilize after July 1. Your visual assessment of plant growth and fruiting can help you know how much to fertilize. If the plants are growing well (10 to 12 inches of new lateral growth each year and new vigorous growth from the base of the bush), leaves look green, and yield is good, there’s no need to worry about whether plants are getting enough nutrients. This assumes, however, that you’ve pruned plants well. Added nitrogen fertilizer will not compensate for poor growth due to insufficient pruning. Check the soil pH every year or two, especially if growth is poor. If the pH is above 6, you can apply elemental sulfur to the surface of the soil or mulch to slowly acidify the soil and improve blueberry growth. Apply no more than 5.5 lb S per 100 feet of row (3 oz/plant). Higher rates will burn or kill blueberry plants. Spread the S evenly under the bushes. Water or lightly rake it into the soil or mulch. Measure the soil pH a year later and add more S if necessary. Ammonium sulfate fertilizers used over a period of years will gradually lower soil pH.
Blueberries need a uniform and adequate water supply from blossom time to the end of harvest. Moisture demand is greatest from fruit set to harvest (time of greatest fruit growth). Fruit bud formation for next year’s crop begins from late July to early August so adequate water is also needed at this time. Plants need from 1.5 to 3 inches of water a week. Irrigate to supplement rainfall as needed. Irrigate frequently enough to prevent the soil from becoming too dry. However, avoid over?watering the plants, or roots may be killed due to lack of oxygen. Overhead watering promotes disease. Drip or another form of under?canopy irrigation is ideal.
After the third year, you need to prune blueberry plants every winter. The best time to prune is January to early March, when plants are dormant. The main objectives of pruning are to promote the growth of strong, new wood and to maintain good fruit production. If you prune too little, plants produce too many small berries and shoot growth is weak. Plants have weak, twiggy growth at the end of the season and fail to develop strong new wood for future production. Severe pruning produces fewer, larger berries and more new wood. If you prune bushes correctly, you’ll have a good balance between fruit production and growth of vigorous new shoots. Experience is the best guide on how hard to prune. A video guide to pruning blueberry plants is available from the Oregon State University Extension Service (A Grower’s Guide to Pruning Highbush Blueberries, DVD 002). Blueberries produce fruit on 1?year?old wood (last year’s growth). Fruit buds are visible during the dormant season. They are the fat buds at the tip of last year’s growth. The small, scale?like buds toward the base of the 1?year?old wood are vegetative buds; they will produce a shoot with leaves next season. The best berries are produced on 1?year?old wood that is from 8 to 12 inches long. Short 1?year?old wood (less than 5 inches long) produces a lot of buds, but fruit quality and vegetative growth are poor. We call this type of wood “twiggy”. When pruning, keep in mind the following principles.
• Keep the bush fairly open. Open bushes promote better air circulation (less disease) and good light penetration to improve fruit bud set for next year’s crop.
• Mature bushes should have 6 to 12 canes at their base, depending on cultivar or growth habit. After pruning, there generally should be an equal number of 1?, 2?, 3?, and 4?year?old canes. If you remove the oldest, unproductive canes, and thin to a few of the best shoots at the base (called “whips?), you will be renewing the bush each year. The following step-by-step system will make pruning easier.
1. Cut out any wood that’s dead, damaged, or diseased.
2. Remove whips smaller than pencil size in diameter, but leave larger whips to develop into good fruiting wood next year.
3. Cut out one or two old, unproductive canes (large stems arising near the base of the plant). Fourth?year or older wood with small, weak growth (short laterals or 1?year?wood) is unproductive. Cut these canes back to the ground or to a strong new whip growing near the base.
4. Remove excess whips (or “suckers?) and weak, twiggy wood, especially from the top of the plant, to allow light to reach the center.
5. Plants may overbear. This often results in very little new growth of wood and small, late?maturing berries. If this is a problem, remove some of the weakest (thin and short) 1?year?old wood. If necessary, also tip back some of the remaining long 1?year?old wood by cutting off about one-third of the flower buds.
Checklist for taking care of mature plants
• Add mulch gradually over the years to maintain a depth of 6 inches.
• Apply fertilizer in the spring, starting around bloom time.
• Water to maintain a uniform and adequate moisture supply.
• Pick fruit at optimum maturity.
• Prune in January or February.
Some cultivars do not produce many whips from the base of the plant. Instead they produce whips from the base of older canes between ground level to knee height. When you prune these bushes, you will have fewer canes at the base of the plant, but more new growth or renewal wood higher up on the bush. Follow the same principles described above.
Each blueberry cultivar ripens berries over a 2? to 5?week period. A well?managed, mature northern highbush plant will produce from 13 to 18 lb fruit. Berries occur in clusters of 5 to 10. Don’t be too anxious to pick the berries when they first turn blue—they are not yet fully ripe. They’ll develop better flavor, become sweeter, and grow about 20 percent larger if you leave them for a few days after they completely turn blue. Pick about once a week or more often in hot weather. Gently roll berries between your thumb and forefinger, removing fully ripe berries and leaving unripe berries for the next picking. You can collect berries in an open container attached to a belt or cord at waist level. This frees both hands for picking. You can keep fruit for a week or more in the refrigerator.
Many species of birds feed on blueberry fruit; they can harvest 100 percent of the berries if you don’t control them. Scare tactics such as aluminum plates and strips of foil flapping in the wind have limited effectiveness; birds become used to these devices. The most effective method of bird control is light plastic netting. You can place nets directly on the plants, but this makes harvesting fruit difficult, and birds can feed on some of the outside fruit by pecking through the netting. As an alternative, you can construct a small wooden or PVC frame over individual plants or groups of plants to support the netting. In general, insects and diseases are not a big problem for blueberries. The following diseases might occur:
• Botrytis (gray mold that kills blossoms)
• Pseudomonas(bacterial blight that causes 1?year?old wood to die back in winter)
• Mummy berry, Anthracnose, and Alternaria fruit rots
Insect pests include root weevils and scale. If insects or disease become a problem, check with your local office of the WSU Extension Service for control recommendations.
Soil test before you plant blueberries
Many people want to plant blueberries. I call it blueberry fever. Gardeners are excited to plant these exotic plants in their gardens. People who want to be blueberry farmers think they can make big money if they plant blueberries. I get calls from people about to plant blueberries, asking what they should do to get the site ready. I always ask “What is the soil pH?” The answer is usually “I do not know” or “Is that important?”
To my mind, the soil pH is the single most important factor in selecting a blueberry site. If the guiding mantra in real estate is location, location, location, then with blueberries it is pH, pH, pH! Blueberries require acid soils. Michigan State University Extension recommends the soil pH be between 4.5 and 5.5. If you plant blueberries in the neutral soils (soil pH 6.5 to 7) favored by most plants, theplants will be yellow and grow poorly if they grow at all.
Iron chlorosis is often the result of planting in soil where the pH is high.
The symptoms are usually found on young leaves and shoots. The leaves
are yellow with green veins. The weak shoot tops are often killed by winter.
Photo credit: Mark Longstroth, MSUE
If you want to grow blueberries, the first thing you should do is test the soil pH of the site to see if the soil is acid enough to support blueberries. Unfortunately, lowering the soil pH is not quick, cheap or easy. Lowering the soil pH is a slow process that may take years. The cheapest way to lower soil pH is to add sulfur to the soil and wait for soil bacteria to convert the sulfur to sulfate to lower the soil pH. This process can take several years and requires hundreds or thousands of pounds of sulfur per acre.
Changing the soil pH is a lot easier and quicker if you do not already have blueberries planted. If the soil pH is above 6 or the soil is heavy clay, I do not think it is worthwhile to try and change the soil pH for blueberries. It simply takes too much time, effort and money. You would be better off to find another high value crop that grows on your site rather than spending a lot of time and money to convert the site for blueberries while other people have good blueberry sites that they can plant with little effort.
There are other quicker, less economical ways to change the soil pH. You can use ferrous sulfate instead of sulfur, but you need eight times as much. Some growers inject sulfuric acid into their irrigation water, but that is dangerous as well as expensive. Homeowners can simply replace the soil for a few bushes, but that is not really practical for a commercial grower with 1,452 blueberry bushes planted 3 feet by 10 feet on an acre of ground.
Blueberries are a long-lived perennial plant and it takes several years to establish a planting of blueberry bushes. You should not expect to harvest fruit for the first three or four years as you grow the bush and it takes 10 to 12 years for a field to reach full production. The initial costs for the first six years are about $15,000 to $20,000 per acre. The growing costs are about $2,000 to $3,000 a year. The first step in planting blueberries is to find out if you can easily grow them on your site. Otherwise they can become an expensive money pit.
For more information see the Lowering the soil pH with sulfur factsheet at the Michigan Blueberry Facts website.
Blueberries require a lower pH than many other fruit and vegetable crops. Before planting blueberries, test the soil to determine the pH level, as well as amounts of nitrogen, phosphorus, potassium and organic matter present. More information can be found in the Soil Testing secion of this article, .
Blueberries require a soil pH of 4.0 to 5.3 for best growth. The primary material recommended for lowering soil pH is finely ground wettable sulfur. Because sulfur reacts slowly and must be converted by soil bacteria, the change in soil pH is brought about slowly; therefore, sulfur should be added to the soil and mixed thoroughly several months to a year prior to planting.
If the soil pH is in the range of 5.4 to 6.0, sulfur can be applied six months before planting to lower the pH. Sulfur also can be applied after planting to the soil surface but not mixed with the soil. Rates of up to 7/10 pound per 100 square feet can be used yearly, if needed. If the initial soil pH is above 6.0, growing blueberries will be difficult unless massive amounts of peat moss or milled pine bark are mixed with the soil. Use 1 pound (2.5 cups) per 100 square feet on sandy soils to lower pH by 1 unit (for instance, from 6.0 to 5.0). Apply 2 pounds per 100 square feet for the same amount of pH lowering on heavier soils containing silt, clay or more than 2 percent organic matter. Try to achieve a pH of around 4.8; too much reduction can be detrimental to bush growth.
Gu, Mengmeng and Keith Crouse. Soil pH and Fertilizers. Retrieved 16 March 2010.
Elina Coneva, Auburn University
Reducing Soil pH
High soil pH can lead to a yellowing of tissue between leaf veins.
Sherry Combs, formerly of the UW-Madison Soil and Plant Analysis Lab
Item number: XHT1151
Is your soil pH too high? Probably not, although the popular press urges most gardeners to question whether their garden soil pH is ‘right’. Only a soil test for pH can indicate whether the pH is ‘right’, and ‘right ‘ really depends on the plant you want to grow and the natural pH of your soil. Turf, vegetables, annual ornamentals and most perennial ornamentals are very tolerant of a wide range of soil pH levels, and acidifying soil is generally not necessary or recommended. Blueberries, rhododendrons and azaleas however, are quite intolerant of alkaline conditions and the soil pH must be maintained at 5.5 or less in order to grow them successfully.
To determine current soil pH, start with a soil test. For soils having a pH of less than 7.5, you should be able to add a soil amendment (e.g., some form of sulfur) and successfully lower pH, if recommended. If soils have a pH above 7.5, adding a soil amendment will probably not reduce pH much because of the ‘free’ calcium carbonate or marl present in these soils. This is an unfortunate characteristic of soils in some parts of Wisconsin. In these soils, consider growing plant species more tolerant of high pH conditions.
Soil pH can be reduced most effectively by adding elemental sulfur, aluminum sulfate or sulfuric acid. The choice of which material to use depends on how fast you hope the pH will change and the type/size of plant experiencing the deficiency. Sulfuric acid (commonly available as battery acid) is fast acting, but is very dangerous, and its use by home gardeners is not recommended. Green industry professionals however, occasionally use sulfuric acid to reduce soil pH around large, established specimen trees. Aluminum sulfate and elemental sulfur can be safely used by homeowners. Aluminum sulfate is faster acting than elemental sulfur because it is very soluble. The advantage of elemental sulfur is that it is more economical, particularly if a large area is to be treated.
In general, it is best to reduce soil pH before planting sensitive landscape ornamentals, rather than attempting to reduce soil pH after plants have become established. Use about 4 to 6 lb. of aluminum sulfate per plant for most medium- and fine-textured Wisconsin soils in order to decrease soil pH by about one unit. If elemental sulfur is applied, decrease the total recommended application by one-sixth. One pound of aluminum sulfate or elemental sulfur is equal to about 2 cups.
As an example, suppose your initial soil pH is 7.4 and you want to plant blueberries which require a pH of no higher than 5.5. You should apply about 8 to 12 lb. (16 to 24 cups) aluminum sulfate, or 1 1/3 to 2 lb. (2 3/4 to 4 cups) elemental sulfur per plant. Be sure to delay planting for about one month after application to avoid root burn.
If plants are already established, use a top-dress application limited to about 1 lb. (2 cups) aluminum sulfate or 1/6 lb. (1/3 cup) elemental sulfur per typical landscape plant. Lightly incorporate the aluminum sulfate or elemental sulfur into the soil, or water-in well. Repeat applications monthly until the total recommended amount of aluminum sulfate or elemental sulfur has been added. Because lowering soil pH is a very slow process, have the soil pH checked about three months after each application to determine if additional applications will be needed. Several applications may be needed on some soils before the soil pH shows any significant change.
Applying certain fertilizers, such as ammonium-containing nitrogen fertilizers like ammonium sulfate, urea or ammonium sulfate, can help maintain acid soil conditions, but these fertilizers will probably not be effective in significantly reducing soil pH. The ammonium in these products reacts in the soil to help maintain the lowered pH. Keep in mind however, that many fertilizer products such as potassium sulfate and gypsum will not effectively reduce soil pH.
Peat moss and certain other organic materials such as pine needles are a good source of organic carbon and can be used to help reduce soil pH. However these organic materials are very slow acting and may not be effective for causing large soil pH changes. Try adding a one to two inch layer of these organic materials and incorporate them into the top six to 12 inches of soil before planting. Afterwards, check the pH. Addition of aluminum sulfate will probably still be needed to ensure that the soil pH is reduced enough for successful gardening.
For more information on reducing soil pH: Contact your county Extension agent.
Links & Downloads
- Reducing Soil pH (PDF)
- Chlorosis factsheet
Tags: soil Categories: Flower Problems, Fruit Problems, Tree & Shrub Problems
Sulfur for Blueberries
Blueberries are distinct among fruit crops in their soil and fertility requirements. They require an acidic (low pH) soil, preferably in the 4.8 to 5.5 pH range.
When soil pH is appreciably higher than 5.5, iron chlorosis often results; when soil pH drops below 4.8, the possibility of manganese toxicity arises.
Do not use Fertilizers containing chlorides or nitrates they harm blueberry roots.
Do not use fertilizer the year plants are set because roots are very sensitive at this time.
Do not apply any fertilizer at transplanting.
Do not Fertilize after flowering as it enhances susceptibility to winter injury.
If the soil pH is considerably above 5.0, you need to add an amendment to lower the pH. Sulfur is one such compound that will help attain the desired pH, the quantity of sulfur uses depends not only on the soil’s pH, but its texture as well.
Seeking advice from a testing service or government agricultural extension , based on your soil conditions is one mode, if this is too costly or simply not feasible, you can test the soil yourself.
Ph test kits are reliable if used correctly, you have to follow the testing instructions to the letter. These tests are simple, inexpensive ways to ensure that your garden has the best foundation possible. Once you’ve ascertained whether your soil Ph is problematic or not, you can work on solving the problem.