Best fertilizer for dahlias

If you like large, single blooms, then pinch off the side flower buds as soon as they are large enough to get between your finger and thumb. Otherwise settle for a central flower and two smaller side flowers, though if you want your dahlias for cutting remember that these side buds are unlikely to open at the same time as the central one.

It is best to disbud the stems if you want them for cutting and to leave them alone if they are to flower in the garden.

Earwigs are the biggest pest. Trap them by stuffing flowerpots with newspaper and upturning them on canes among the flowers. The thing is, earwigs are voracious feeders on aphids as well as dahlia flowers so it’s a shame to wage war on them.

Dahlias are among the easiest plants to please. The taller kinds need a stake to which the stems can be tied in, but the shorter ones are self-supporting. Tasteful? Who cares; they are part of the garden’s late summer beauty.

Don’t miss Alan’s gardening column today and Tip Of The Day every weekday in the Daily Express. For more information on his range of gardening products, visit alantitchmarsh.com.

By Cari Peters|November 26, 2012

Dahlias can be grown from seed, plugs, liners or tubers. The newest dwarf varieties have brought intense color and appeal to our customers, which makes this crop a staple value-added selection for the early spring holidays.

Fertility Early On

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In propagation, dahlias prefer to be kept in evenly moist media at a pH below 6 (5.5 to 5.8). Before the signs of first leaves, begin to fertilize with calcium-based formulas, like 15-0-15 or 13-2-13 at 75 ppm. The calcium in these formulas is associated with nitrogen as NO3, which is easily taken up by newly forming root systems. After seven to 10 days, increase your fertilizer rate to 100 to 150 ppm using the same formula for another seven to 10 days. After these initial two weeks, you can use the same formula selection or incorporate a more potentially acidic fertilizer like 21-5-20 as an alternative to keep the pH of the root zone in the target range of 5.6 to 6.0. Early targets for media EC are between 1.2 and 1.5 mS/cm.

The Building Blocks of a Strong Plant

Testing your water source is a fundamental step in choosing the fertilizer that will match up with the existing nutrients in your water. Dahlias are heavy feeders, especially when they enter into the long-day stage. Nutrient demand will grow as day length and light levels increase, therefore it is important to provide a balanced nutrient profile at the start of this stage. This includes providing all the major, minor and secondary nutrients from either your water source or your fertilizer selection. Calcium and magnesium may have to be supplemented to reach minimum levels of 60 to 80 ppm calcium and 30 to 50 ppm magnesium.

For dahlias, a strong and nicely branched root system will add stability to the container as the plant begins to produce large and colorful flowers.

Once a sturdy root system is established, it is recommended to increase the fertility levels to a much higher rate. How do you know if it is the right time? Examine the root system by tapping the plant out of the pot, being careful to support it so as to not break any stems or leaves. If you can see healthy, white roots extending to the edge of the pot, you can be sure that the root system can start to absorb a higher rate of fertilizer.

A Fantastic Finish

We have talked in previous articles about formula selection. Similar rules apply to the fertility choices for growing the different types of dahlias. Very briefly, high alkalinity and high pH water sources should use a potentially acidic formula, like 21-5-20, 25-5-15 or 20-3-19. If it is necessary to supplement with magnesium, you can add Epsom salts directly to your stock tank. A conservative rate of 4 ounces per 100 gallons of water will achieve an increase of 30 ppm magnesium in the nutrient solution.

Low alkalinity or pure water should aim to increase or maintain media pH by adding calcium at each feeding. Complete formulas such as 13-2-13, 15-5-15 or 15-2-20 are very good options since they add both calcium and magnesium in one balanced formula. However, they will raise your pH over time.

Neutral formulas such as 17-4-17 and 16-2-15 also add calcium and magnesium but are designed to keep the pH change in the root zone to a minimum. Compare these factors when selecting your fertilizer, so you can provide a balanced nutrient profile as well as keep within the pH target values.

When the root system is established, gradually increase your overall fertilizer rates to 250 to 300 ppm and maintain these EC and pH targets until right before ship or sale date. All programs should still use a lower-phosphorus formula to prevent internode stretch. Monitor growing media to avoid a gradual rise in pH and EC. Do not exceed a pH of 6.2 and EC of 2.5 mS/cm.

Taking the plant to finish, many growers can switch back to the early calcium containing formula (15-0-15 or 13-2-13) at a lower rate (100 to 150 ppm) to harden off the plant while also alternating with a higher phosphorus formula, such as 15-15-15 or 15-16-17. This routine will surround the roots with available phosphorus and stimulate the plant to stop focusing on leaf growth and start focusing on flower production.

Common Fertility Issues

Growing dahlias for the early spring window can easily boost your initial spring or Mother’s Day sales, but there are some common issues to be aware of.

Underfertilization due to overwatering or overall low fertilizer rates will cause soft growth and premature flowering. As light levels and temperature can spike in the early spring, growers must take care to maintain the higher fertility rates as the plant increases transpiration.

Need a little bit of green? As plants go to bloom, make sure you are maintaining dark-green foliage. Use a specialty iron fertilizer, like Jack’s Petunia Feed 20-3-19. This formula contains a proprietary blend of the three iron chelates (EDTA, DTPA and EDDHA) that will give your chlorotic tissues a greening boost, even if the pH is a bit on the higher side. Use a rate of 200 ppm in place of your potentially acidic fertilizer for two or three feedings, then return to your normal fertility routine.

Overfertilization will cause more vegetative or leaf growth and less flower production, especially at the end of the crop. At the early stages of growth, light levels are low, so pay particular attention to the nitrogen form in the fertilizer you choose. Keep ammonium (NH4) nitrogen levels in the root zone at less than 15 ppm by choosing high nitrate (NO3) based fertilizers like, 13-2-13, 15-5-15 or 15-0-15. These formulas are designed with a balance of nitrogen that is easy for the plant to absorb along with low, but readily available, phosphorus to encourage the growth and branching of a healthy root system.

Dr. Cari Peters is vice president at J.R. Peters. You can e-mail her at See all author stories here.

Contents

Dahlia Care

Dahlias are grown from tubers and not bulbs. Tubers have “eyes”, for example a potato is considered a “tuber.” Bulbs, such as tulips and daffodils, can be planted in the fall when the ground is cold and wet. Dahlias must be planted in the spring when the soil has warmed to a temperature of between 55 – 60 degrees. We plant in mid May in the Pacific Northwest.

Soil Preparation

The best place to plant your dahlias is in an area that’s already a garden area that has basic top soil. To prepare for planting, amend your soil with a 4″ layer of compost on the garden bed and till/work in before you plant.

*** If you are creating a brand new area for planting: Use 3-Way Top Soil, which is a mixture of top soil, manure and sand. 3-Way can be delivered by your local nursery or you can buy it by the yard and haul it in your truck or trailer.

Where to Plant

Minimum sun requirements for dahlias is 6 hours per day. Plant your dahlias in a sunny location that receives at least 6 hours of sun per day. Morning sun/afternoon shade works best in warmer climates.

When to Plant

Don’t plant to early, dahlias need the soil to reach 60 degrees for best results. Planting time in the Northwest is around Mother’s Day. Areas in the far north, such as VT, NH, MN, MI, planting time is late May or as temperatures allow. Central US, in April when soil allows. Warmer, southern states are usually safe to plant late March, early April, or as temperatures allow. Delay planting if you’ve recently had heavy rains that have resulted in soggy soil. Dahlias like to be planted in moist soil, that is not water-logged.

Planting

Space your dahlias 18″ – 24″ apart, 12″ for a fuller, more grown together look.

Lay the dahlia tuber on its side (flat), about 6″ deep with the eye of the tuber pointing up. Cover with soil.

Dahlia Barn Field – North Bend

Watering

DON’T WATER WHEN YOU PLANT !! That’s hard to do with new plantings, but spring time offers all the moisture the tubers need. Do not water until the sprouts appear above the ground. An exception would be an extremely dry climate where the soil would need moisture added, dahlias do need some moisture to the soil to get growing. If your soil has plenty of moisture, don’t add extra water at planting time. Dahlia tubers are susceptible to rot after planting, especially in soggy, wet soils. At first, it’s best to keep the soil on the dry side, rather than the wet side. When you see the sprout above the soil, begin watering 2-3 times per week with a deep soaking.

Easy Watering

We highly recommend using soaker hoses to water your dahlias. The water goes directly to the root zone and keeps the leaves dry, preventing fungal diseases. Run the water as long as it takes to deep soak the soil to a depth of around 6″ minimum. We generally have to run our hoses for 45-60 minutes to get a deep soaking in Washington State. Warmer, dryer climates may need to water at least every other day. Once the dahlia has sprouted, a deep soaking 2-3 times per week in the summer is sufficient. The soil should never completely dry out or they will stop growing properly.

How long until they bloom ?

Small-medium bloom size dahlias will take about 90 days to bloom. Large dinner plate dahlias will take about 120 for bloom. Soil moisture is so important at this time. Be sure to supply your dahlias with enough water to keep them growing strong and healthy.

Fertilizer

Dahlias require low nitrogen fertilizers. We recommend fertilizers with a 5-10-10 ratio, or as close as you can find to a 5-10-10 ratio, within 30 days of planting and again 30 days later. Do Not overfeed your dahlias, doing so will promote lots of foliage, but not a lot of bloom. Fertilizer makes foliage and water makes bloom. Proper watering and good soil will create the best flowers.

Weed Control

Hand weeding is the only type of weed control you should use. Using herbicides around your dahlias is risky!

Pests & Problems

Can you spot the deer?

SLUGS LOVE DAHLIAS !! Especially as they are emerging from the soil. Use the slug bait of your choice until your dahlias are at least 12″ tall. After the dahlia has reached full height, no slug bait is necessary.

DEER – We find that deer DON’T like dahlias, but they will eat what they want if they get hungry enough. Deer do stroll through our gardens, eat blackberries and apples, but leave the dahlias alone.

EARWIGS – Not much can be done about earwigs. You can spray over-the-counter insecticides or insecticidal soap. Granular insecticide sprinkled on the soil in the springtime will help as well.

Pinching your Dahlias

To promote a compact, bushy plant with more blooms, pinch out the center growing tip right above the 4th or 5th full set of leaves, when the dahlia is 18″ – 24″ in height. This will create a stronger, more manageable plant with more blooms. It will also make the plant less top heavy to where you have a need for staking.

Cut Flowers

The more you cut dahlias, the more they will bloom !! You want to cut yourself a long stem as well, even it if means taking the 2 side buds. This will promote more growth and more blooms. We tell customers to cut a stem no shorter than from your wrist to your elbow, minimum even if it means taking the side buds. We find, the side buds to be weak flowers. This will promote lots of growth and make for a healthier, more manageable plant with lots of blooms. Dahlias are work horses and love to be cut.

Diseases

Dahlias can be susceptible to powdery mildew and other types of fungus when they are in wet conditions. Keeping the leaves dry as possible will help to control fungus, because fungus thrives in wet conditions. At the first sign of any fungus, spraying with any type of fungicide every 7-10 days, until the fungus is under control. Preventative sprays can be used to control fungus from starting and spreading. Neem oil*, derived from the ‘Neem Tree’, is an organic approach and is a natural Fungicide, Insecticide and Miticide. It also makes the leaves shiny and green and can be used up until and even after the dahlia is in bloom. *You can find Neem Oil at most garden centers.

Digging Dahlias

Wait until your dahlias look like this before digging !!

WAIT FOR YOUR DAHLIAS TO FREEZE IN THE FALL !! Don’t be in a hurry with your dahlias, they need to feel the cold. Then wait at least 1-2 weeks before you dig them up. Leave them intact and don’t cut them down. Wait until the foliage has turned black and have completely died back. During this time, the dahlia is ‘ripening’ and preparing itself for winter. Dahlias dug too early will not store over winter. After the foliage has died back, cut the stems to a height of 6″-8″. Use a shovel or pitchfork to gently loosen the soil and lift the clump out of the soil. Tap off the soil from the clumps and allow the clumps to dry in an area above freezing for at least 3-5 days. You can divide then or leave in a clump and divide in the spring. Then store for winter.

What if I live in an area that doesn’t freeze?

You are safe to dig around mid-November if you haven’t gotten a freeze. Start to with hold water for about 2 weeks before you dig, around November 1st.

Do I really need to dig up my dahlias?

Digging and dividing will keep your dahlias returning year after year when they are dug and stored properly. Dahlias left in the ground will create a massive tuber clump underground that will send up many weak, unproductive stalks that have small blooms. Eventually, if left undug year after year, they won’t come back at all. You can treat your dahlias as annuals and purchase new tuber stock each year.

If you live in an area that does not have harsh, freezing winters, your dahlias may survive winter without digging. In the fall, wait at least 1 week after a freeze and after your dahlia stalks have died back completely. Then cut the stalks down to the ground and place a 10″-12″ layer of mulch such as grass clippings, leaves, straw or compost. This will protect your dahlias over winter. In March, remove the layer of mulch so that the soil can begin to warm up. Dig up the tubers, divide, let dry for 3-5 days, and replant them when it’s the correct planting time for your area.

Although, we do recommend digging, dividing and storing in the fall, you should have success with this method as well.

Dividing Dahlias

Tap and brush all the soil off the dahlia clump. When dividing dahlias, the first thing to do is to remove all broken tubers, remove the original ‘mother’ tuber and remove any tubers that are rotten. You can divide now or keep the cleaned-up clump in tact and divide in the spring. In the spring, the eyes are easier to see. It’s very important to get a piece of the swollen part that is attached to last years’ stem. The eyes will emerge from the swollen part of the dahlia that is attached to last years’ stem. If your tuber does not have an eye, it will not sprout. Choose only strong, firm tubers. Weak tubers that show signs of rot, shriveling or decay should be tossed and not used in the garden.
Cut surfaces should be allowed to dry thoroughly before they are planted in the garden or stored for the winter. Lay out to dry for 3-5 days in a place that will not freeze, then store for the winter.Our step by step tutorial of the tuber dividing process:

Just look at or Print a printable copy (PDF)

Winter Dahlia Storage

There are many different ways to store your dahlias. Choose the method that you think would be right for you. If one method doesn’t work, try different ways of storing from year to year and stick with what works best for you.

The most important tips are:

  1. Make sure they freeze in the garden and the stalks turn black before they are dug up. During this time, the skins are thickening and they are preparing themselves for winter. Dahlias dug too early typically will not store over winter.

  2. Once dug up, make sure they never freeze wherever they are stored-an attached garage or a cellar is usually pretty safe.

  3. Make sure they are VERY DRY before they go into storage.

Storage options are:

  1. Store in clump form or divided loose in paper bags or cardboard boxes lined with newspaper and filled with peat moss.

  2. Cardboard box lined with newspaper, add a layer of peat moss, add a layer of dahlias, another layer of peat moss, etc until the box is full. This can give you an added layer of protection from freezing and keeps humidity higher.

Keep the temperature at 40-50 degrees at all times during winter storage. The humidity should be kept medium-high to keep tubers from drying and shriveling. Check your tubers monthly during winter storage. In the spring, after all danger of frost has passed, bring your dahlias out and divide them if you didn’t already divide in the fall. Let the fresh cuts dry for 3-5 days, then plant in the garden when it’s the correct planting time for your area!!

Dahlias do require a fair amount of care and maintenance throughout the year, probably more than the average garden plant. But for all your work, you will be rewarded with armloads of fresh cut flowers during late summer when most other garden plants have finished their bloom. Cut the flowers and enjoy their blooms. The more you cut them, the more they will bloom.

Value hides in dahlias’ edible tubers and petals

FANCY a good feed of dahlias? Not on, you say, dahlias are flowers not food.

Well, not exactly.

The Aztecs loved little better than munching on the sweet potato-like tubers of dahlias. In

fact, dahlias were first taken from Mexico to Europe in the 16th century as a food crop. When people saw their vivid blooms, they started growing them in gardens.

According to those who savour them, dahlia tubers can be eaten raw or cooked and the key is finding the tastiest.

media_camera Dahlia tubers.

Several years ago a Swiss company taste-tested a selection to discover the best. The result was a collection of six called DeliDahlias.

Among the collection was the popular Austrian-bred, dark red flowering Dahlia Black Jack, available in Australia and hailed for its delicate asparagus flavour.

When peeled, dahlia tubers appear much like other root vegetables. Dahlia flowers can also be eaten and are used as a garnish or chopped in salads.

According to local plant and seedling production company Oasis, the flavour of the flowers and tubers are dependent on the soil and conditions in which they are grown.

It recommends adding sweet and spicy petals to summer salads for flavour and colour, and the tubers being used for their crunchy texture and flavour, varying from spicy apple to carrot.

Word of warning — at least one US university advises tubers can be toxic if you eat too many. Other authorities suggest cats and dogs can suffer mild gastrointestinal pain after eating them.

Is there anything as glorious as a dahlia in full bloom? Lush, vibrant and colorful, this exceptional plant is surprisingly easy to grow – you don’t need to be an expert. Here are some tips on how to plant, grow and care for dahlias.

Planting Dazzling Dahlias

When should I plant my dahlias?

Soil—not air—temperature is the key to healthy, beautiful dahlias. You’ll want the soil temperature to be 60 degrees or warmer. For the coldest Northern states, your soil won’t be ready until May, while those enjoying warmer climates might be good to go as early as March. Resist the temptation to plant them earlier than advised: your tubers may just rot. To determine whether your soil is ready, buy an inexpensive soil thermometer, and test the soil mid-morning. Basically, if you can garden in a t-shirt, you’re probably ready to start growing!

Location

Where should I plant them?

Like petunias, sunflowers, and lavender, your dahlias will thrive on generous sun exposure. Choose a place in your garden that receives 6 to 8 hours of sun a day. If you live in a very hot climate, a little afternoon shade can’t hurt. If you’re struggling to find a patch of land that gets full sun, try the lower growing or dwarf dahlias. The more sun, the more flowers you’ll get.

Healthy Soil, Healthy Plants

What sort of soil should I have?

Whether you’re planting in the ground or in a pot, you’re ready to plant your dahlias if your soil is:

  1. Slightly acidic. Aim for a PH level of 6.5 – 7. Add lime to increase the level, or sulfur to decrease it.
  2. Well-drained. Avoid planting dahlias in soil that pools after it rains. Too much water will cut off the oxygen your tubers need.
  3. Healthy. Give it a boost of nutrients with cow manure.
  4. Free of herbicides. Make sure your potting soil hasn’t been sterilized. Even if a herbicide claims to be safe for flowers: don’t use it. Always hand weed. Also, add compost sparingly. Compost tends to be high in nitrogen, which produces less robust, full plants.
  5. (If you live in a hot climate) Slightly damp. Just a little moisture is enough.
Planting your Dahlias

How do I plant my dahlias?

If your tubers have any sprouts attached to them that are longer than 1”, carefully trim them back to just 1”. Plant your tubers in holes that are 6 inches deep, and 18-24 inches apart, depending on how big the varietal you’re planting. Insert your garden stakes right next to each tuber. Any kind of stake is fine (metal, wood, plastic etc.), and it is best to stake now before they sprout. Throw in a handful of bone meal—it’s a great fertilizer and source of phosphorus and protein—but only if you don’t have pets. (Rover and Fluffy might dig it up.)

Don’t cover your garden bed with mulch or bark dust, because you need the sun to keep the soil nice and warm. Add snail and slug bait — dahlias do tend to attract slugs. Unless you live in a hot climate, you don’t need to start watering until after your tubers have sprouted, which will be in 3 to 5 weeks. Seriously! Over-watering is one of the main reasons dahlias fail to bloom.

Containers and Pots

Can I grow dahlias in a container?

Even though dahlias do grow best in the earth, rest assured, you can grow them in a pot. Try the low growing and dwarf varietals: they don’t need as much space and soil. A 12 x 12-inch pot is fine for these types. Aim for two parts garden or topsoil, and one part potting soil.

Watering Your Plants

How often should I water them?

After your dahlias are above the ground, they’ll need a deep watering 2 to 3 times a week: enough moisture to reach your planted tuber. A hose is best. Remember, you only need to water unsprouted tubers if you live in hot, dry climates like Texas or Southern California: in this case, water lightly once or twice a week.

Fancy some Fertilizer?

Should I fertilize my dahlias?

If you choose to use a fertilizer, go for a low nitrogen or slow release type. Use cow or steer manure at any point in the planting/growing process. Get the processed/bagged kind. Only add fresh manure in the fall, so it has time to break down before spring. For commercial fertilizers, again, go for low nitrogen and high in potassium and phosphorus, something like a 5-10-15 or 5-10-10. Fertilize within the first month of planting, then repeat again 3 to 4 weeks later: don’t overdo it.

The Need to Weed

How should I weed my dahlias?

The thing about weed killers is, if they kill the weeds, they also kill your dahlias. Hand weeding is the best, low-impact way to keep weeds out of your garden beds. If you absolutely must use a commercial weed-killer, try something like Round-Up but only after your tubers have sprouted, and be careful not to spray the plant itself.

Topping

How should I top my plants?

If you want to display your dahlia flowers indoors, then you’ll want the best possible stem length. Simply cut the center shoot just above the third set of leaves, when your plant is about twenty inches tall. This will help bloom a shorter, bushier plant.

Digging & Storage

How should I dig and store my dahlias?

After your dahlias have turned black from frost, snip the stems at about 6 inches, and carefully dig out your now sizable tubers. Wash off the dirt and leave them in the sun to dry. Then pack them in some peat moss, sand or sawdust in a paper bag or box: never plastic and never fully sealed. Store them in a cool, dry area (not a freezer) until you’re ready to plant next spring. If you live in a mild climate, you can try leaving them in the ground: just cover the surface with mulch or similar, to protect the soil from rain and freeze.

Divide (and Conquer)

How do I divide my dahlias?

Cut your tuber clump with a sharp knife to separate out the roots: each root must have an “eye” located in the center stalk in order to grow. You can do this in the spring or the fall. If you can’t see the eye (and not all tubers have one), try dividing your clump into halves or quarters.

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