Yellow leaves on gardenia

Gardenias are admired for their glossy green foliage and fragrant blossoms. However, gardenias are particular about their growing conditions and require consistent maintenance in order to keep happy and beautiful. Once you understand what a gardenia needs to survive, growing them is very rewarding.

Basic Gardenia Care and Growth Requirements

Gardenias are often found outside in southern regions. They are grown as ornamental shrubs in warm regions and as patio plants that are brought indoors in cooler areas. Paying attention to the particular growing requirement of gardenias is especially important. If you provide the gardenia with the right conditions, it will reward you with vibrant foliage and a proliferation of fragrant blooms.

Soil

Well-drained, acidic soil with a pH of 4.5 to 5.5 is ideal for gardenias, whether potted or in the ground. During the day, gardenias prefer temperatures from 68 to 74 degrees with a low of 60 degrees at night. Moderate humidity assures a healthy plant but soggy roots cause flower buds to drop, as will soil that is too dry. Adding peat moss to the soil will benefit your plant by helping it retain moisture without becoming too wet.

Water

While the gardenia likes humidity, misting the leaves can cause problems. Water droplets can lead to fungal growth on leaves. This is important to keep in mind if you plant your gardenia outside. You don’t want to place it under plants that drip onto its leaves. You must also be careful your plants are not crowded too close together. A lack of air flow also causes fungal issues.

When you water potted plants, check to see if the top inch of soil is dry by poking your finger into the soil and then give your plant a good soak. Any water that accumulates in the tray under the pot should be drained out. It is a great idea to place gardenias in a pebble filled tray. Water can be poured over the pebbles to provide moisture and humidity without excessive water being absorbed into the soil.

Light

Outdoor gardenias prefer full sun, with some shade in the hottest summer months. Indoor gardenias should not be placed in direct sun, but in a room that gets plenty of bright, indirect light.

Temperature

Temperature is considered one of the most crucial aspects of growing a gardenia. When daytime temperatures are above 70 degrees F or if night temperatures are over 65 degrees F or below 60 degrees F, flower buds will not form. Keep your gardenia between 65 and 70 degrees F during the day and 60 to 62 degrees F at night.

Fertilizing

Feed gardenias every three weeks during the growing season with an acid-based fertilizer.

Outdoor Gardenia Care

If you are fortunate enough to live in a climate where these tropical plants will grow outdoors (zones 8-10), you may want to plant one near a window or patio to fill the air with its intoxicating scent. The process is simple as long as you remember the basics of gardenia plant care.

Take Care When Planting Outside

Be sure to plant your gardenia in well-draining soil conditioned with peat moss and organic matter. Dig a hole twice the size of the gardenia’s root ball and just as deep as the container. When you place the plant into the hole, be sure that the top of the root ball is slightly above the soil’s surface. Mound a mixture of native soil and peat moss around the plant and tamp down to eliminate air pockets. Water thoroughly and keep well-watered during the growing season.

Tips for Outdoor Gardenia Health

There are several things that you can do to improve the health and longevity of your outdoor gardenia plant. If you take good care of your plant, it will perform to its maximum potential year after year.

  • Prune: While it is fine to cut gardenia plants back as far you would like in order to shape, be sure to do your pruning when the plant is dormant. Use only clean pruning shears and do not cut all of the leaves off of the plant.
  • Mulch: Mulch will help with moisture retention. You can use pine needles, bark, finely shredded bark or other organic matter. Provide a mulch covering that is two inches thick and do not allow the mulch to touch the trunk of the bush.

Avoid Common Gardenia Pests

The best way to protect any plant from pests is to keep it healthy and prevent over-crowding. Other common causes of insect problems include allowing too much moisture to sit on the leaves and not maintaining the proper temperature and moisture levels. Keeping gardenias in the proper conditions goes a long way toward protecting them from common pests.

Gardenias are vulnerable to various insects including:

  • Aphids
  • Mealy bugs
  • Spider mites
  • Thrips
  • Scale
  • Whiteflies

Beautiful Blooms Are Your Reward

While gardenias are picky about their care, if you are patient and remember the basics, your efforts will be rewarded. A beautiful blooming gardenia is worth it.

  • Gardenia flowers
  • Pruning a gardenia
  • Gardenia roots
  • Don Burke transplanting gardenias
  • Gardenia cuttings
  • Sick gardenia leaves

Gardenias are an outstanding flowering shrub with an exquisite perfume that creates a magical, romantic atmosphere in the garden.

They flower at their best in the warmer months of the year usually from November to May. Their large creamy white flowers and glossy green leaves also make them very attractive garden plants.

Characteristics of the Shaw’s garden

Don Burke awarded John and Carmen Shaw’s garden the inaugural Burke’s Backyard gardening excellence award because the gardenias in their garden were the best he had ever seen. What is their secret to growing such healthy gardenias in an area that is not ideal for this semi-tropical plant? The location is subject to frost with winter overnight temperatures falling to -4°C. The owners have created a microclimate around the house so that the plants would not get frost-bitten in winter. The house is brick and there is extensive brick paving which absorbs the heat from the sun during the day and radiates it out at night creating a frost free zone. (See diagrams).

Agricultural piping was laid throughout the garden before major works began thereby ensuring excellent drainage. As well as that, the gardenias were planted in raised garden beds with an irrigation system installed so that the sprinkler heads were underneath the foliage of plants. Undoubtedly the most important key to the success of the gardenias is their nutrition. The area was previously a dairy farm which was heavily fertilised to ensure constant grass production for the cattle. Nutrients were also recycled in the form of manure.

The existing richly fertilised soil was then made even richer by the addition of a special soil mix from Australian Native Landscapes (ANL). To every four parts of ANL’s standard organic mix they added one part of duck litter and one part of mushroom compost. The organic garden mix itself is made up as follows:

  • 50% black soil
  • 20% coarse sand
  • 0% of organic mix composed of composted sawdust, composted pine bark fines, spent mushroom compost and coffee grounds.

As you can see, this is an incredibly rich mix. The mix was added throughout the garden to a depth of at least 200mm (8″). This had the effect of raising the height of the beds.

In addition to the rich soil, once the gardenias were planted they were fertilised yet again with a slow release fertiliser, Multicote by Haifa Chemical Ltd ( N:P:K 18:2.6:9.9) 8-9 month release fertiliser. During the early establishment the plants were watered several times per week but since establishment are only given a good soaking once a fortnight via the well designed irrigation system. The plants are fertilised with Multicote each spring and again during summer. The plants are growing in full sun through to part shade.

It is generally believed that an acid pH is critical in order to grow good gardenias. The Shaw’s soil tested at pH 6-7 which is only slightly acid. In summary the conditions in the Shaw’s garden provided excellent drainage, warm microclimate, rich organic soil, regular deep watering and lots of fertiliser. These conditions are similar to those in nurseries where potted gardenias are grown.

Details

Common name: Gardenia, Florist’s Gardenia.

Botanic name: Gardenia augusta. The most commonly grown variety is called ‘Florida’.
Other varieties: ‘Prof. Pucci’, ‘Fortuniana’ and ‘Magnifica’, which have larger flowers. ‘Golden Magic’, which has flowers that turn yellow with age. ‘Radicans’ is a dwarf form with a prostrate habit (up to 0.5m high by 1.5m spread or 20×50″), making it an excellent ground cover. It has smaller flowers and leaves and tends to have more cold tolerance than ‘Florida’. ‘Aimee Yoshiba’ is a newer variety which has large deep green leaves and is said to be the best of the larger flowering gardenias.

Other species: G. thunbergia (the star gardenia) has a tubular flower and more cold tolerance than the G. augusta. It is a native of South Africa. It is a better choice for Adelaide and environs.

Climate (see map):

Gardenias are warm climate plants which are at their best in a mild, humid climate. They are seen to perfection in frost free areas north of Sydney and Perth but will grow in Adelaide and Melbourne in a warm spot. The gardenia is native to eastern Asia (China, Taiwan and Japan).

Best look:

  • Gardenias are excellent for mass plantings or as a hedge. Grown as a standard, gardenias look great in a pot.
  • Will perform well for years in a large pot growing in a quality potting mix.

Good points:

  • Fragrant and beautiful creamy white flowers which are seen from late spring to late autumn with the main flush in the months leading up to Christmas.
  • Can be picked to use as a button hole or posy (but handle flowers with care as they bruise easily).
  • Attractive evergreen small to medium shrub (1-2m or 3-6′ tall and maybe as wide) with deep green foliage.
  • A versatile shrub which can be grown as a hedge or a standard or used as a background planting.

Likes:

  • Slightly acidic, cool, moist, well drained soil.
  • Some shade, particularly from the full summer heat in a hot or tropical climate. In cooler areas they are quite happy in full sun.

Care:

  • Water well, particularly from spring to summer when plant is flowering.
  • Protect from hot afternoon sun.
  • Prootect root system with a mulch of lucerne hay, compost or well-rotted wood chip.
  • Little pruning needed unless being grown as a hedge.
  • Feeding in spring and summer with Osmocote, Multicote or Dynamic Lifter.

Hates:

Frosts and cold climates although as seen in the Shaw’s garden, warm microclimates can be created in frosty areas.

Downside:

As with all popular plants there are some common problems with gardenias.

  • Buds falling or failing to open and going brown: Gardenias tend to keep producing flower buds right through autumn even though their growth is slowing. They will often hold these buds right through winter and drop them in spring. This is fairly normal. The buds can also drop as a result of being damaged by weevils or leaf hoppers.
  • Yellow leaves (particularly seen in spring): In the past leaf yellowing has generally been attributed to a magnesium deficiency and treated with applications of Epsom salts (sulphate of magnesium) but the plant is probably more in need of an all purpose fertiliser and a good watering. Apply fertiliser in spring when weather begins to warm and yellow leaves begin to show.
  • Nematodes: If the yellow leaves don’t pick up after fertilising and particularly if there is wilting and if you have a sandy soil, check for nematodes on the roots. Nematodes cause cream, warty lumps on roots (about the size of a match head), yellow leaves and wilting. You could treat the soil with Nemacur, but this is a potent chemical which we do not recommend for general use. If the area is sunny, a planting of marigolds may also help deter the nematode.
  • Scale and mealy bug: Scale is commonly found along the stem and on the back of the leaves. Mealy bugs tend to hide among leaf nodes. Treat scale with PestOil. Follow up applications may be necessary.The presence of these insects also suggests the plant is under stress. Make sure it is well watered and correctly fertilised.

Availability

Multicote fertiliser is available from Elders throughout Australia. Cost is $24.75 for 4 kg and $90.20 for 25 kg.

Copyright CTC Productions 2006


Helping A Gardenia Bush With Yellow Leaves

Gardenias are beautiful plants, but they require a bit of maintenance. One problem that plagues gardeners is a gardenia bush with yellow leaves. Yellow leaves are a sign of chlorosis in plants. There are several causes and trying to determine the reason can involve a lot of trial and error.

What is Chlorosis in Plants?

Chlorosis in plants simply means that the plant doesn’t have enough chlorophyll. This can be caused by poor drainage, root problems, pH too high, or not enough nutrients from the soil, or a combination of all of these.

Too much water causing a gardenia bush with yellow leaves

When you have a gardenia bush with yellow leaves, the first thing to do is check your soil for too much water. The gardenia needs moist soil, but not overly wet. Add some more compost to help it have a richer environment and be sure to set up proper drainage.

Wrong pH causing gardenia bush with yellow leaves

Once you determine that water isn’t the issue, you need to check the soil’s pH balance. Soil pH for plants is an important issue for gardenias, which require a pH between 5.0 and 6.5. The effects of soil pH level on plants will cause it to not be able to absorb minerals like iron, nitrogen, mannesium, or zinc. Mineral deficiency is one of the major causes of chlorosis in plants and in gardenias the most common deficiencies are magnesium (Mg) and iron (Fe), which result in similar leaf yellowing. Treatment for each is dependent on proper identification:

Magnesium deficiency – Yellow leaves at the base of branches while tips remain green. Will also notice dark green triangle at leaf base that may resemble the plant’s leaf shape. Dose of magnesium salt, or Epsom salts, will help. However, keep in mind that excessive applications may leach into soil.

Iron deficiency – Tips often yellow but the base of branches and leaf veins remain green. Most common as weather becomes cooler since slower plant sap makes it more difficult to take up the nutrient. Therefore, spring is normally deemed the most appropriate time for treatment through use of iron of chelate, which lasts longer and absorbs gradually. Powder form is recommended as liquid types may not have sulfur, which is necessary for lowering pH (iron decreases as pH increases).

It can be difficult to balance soil pH for plants. By adding the missing nutrients, you can help reduce yellow leaves on your gardenia. One method is to simply add the right balance of the missing nutrients to the soil around the plant (starting at about 5 feet away from the plant). Some people treat the leaves with a water solution of the missing nutrients, but this is a temporary fix at best, as it helps the current foliage turn green again. It is better to adjust the soil pH for plants for long term health. Adding the nutrients directly to the soil, about 3 feet (or further) away from the plant where the roots spread out is another way to help eliminated yellow leaves.

A gardenia bush with yellow leaves is a common problem and can be very difficult to ultimately fix. If, after your best efforts, your gardenia still does not survive, don’t be too hard on yourself. Even master gardeners with years of experience can lose gardenia bushes despite their best efforts. Gardenias are a beautiful but fragile plant.

How to Fix a Gardenia Plant that’s Starting to Get Yellow Leaves

Dark green shiny leaves are one of the biggest selling points and also one of the most noticeable qualities of a gardenia plant. That’s why it’s always a huge concern when you notice that the gardenia leaves are starting to turn yellow. There are several things that can contribute to the leaves turning yellow, and also some steps you can take to try to fix this issue before it ruins the natural beauty of the gardenia plant.

Why the Gardenia Leaves are Turning Yellow

Gardenia leaves turning yellow is a huge concern for people and often times they don’t know exactly what’s causing the issue. There are a few different possibilities when it comes to why these dark green leaves are suddenly turning yellow and it’s vital you figure out the issue quickly. The quicker you figure out the issue and correct it, the better chances that you can save your plant.

1. Over-Watering or Under-Watering

The leaves on your gardenia plant might be turning yellow due to over-watering or under-watering. Watering issues are one of the most common reasons for the leaves to turn yellow, since these plants require a specific amount of water. You really should give your plant one-inch of rain or the equivalent in watering each week.

The plant should not be too soggy but also cannot be too try, so it’s important to find the balance of it being moist but not overly-saturated. If the plant becomes too wet, then you could end up with fungi and other diseases that could damage the entire gardenia plant.

2. Poor Soil Drainage and Root Rotting

Poor soil drainage and rotting of the root can cause yellowing leaves. The plant might not be getting enough chlorophyll, which is common when there is a drainage problem or problem with the roots, such as rotting. If there is not proper drainage, then the soil will become too wet, which goes back to it being overly-saturated with water. Fungi can develop and end up turning into root rot if there is too much water and not enough drainage happening as well.

3. Gardenia is Not Getting Enough Sunlight

The gardenia plant is very temperamental and it requires just the right amount of sunlight to thrive. Both too little sunlight and too much sunlight can damage your gardenia plant. It’s best if the plant has the morning sunlight but the afternoon shade if you are growing this plant in hotter climates or if it’s summer.

If you live in cooler areas, then the plant can survive on full sunlight. The gardenia plant can get too much direct sunlight if you are in a warmer climate. Too much sunlight can cause the buds to begin falling off, the leaves to turn yellow, and the plant to become scorched. It’s important that you provide the gardenia plant with just the right amount of sunlight per day in order to keep it healthy and prevent situations where the soil will get too dry due to the over-abundance of sunlight.

4. Lack of Nutrients in Soil

Gardenia plants require a pH somewhere between 5 and 6.5 and if this pH is off-balance, then the plant will not be able to take in the vital nutrients it needs in order to grow. Iron, nitrogen, zinc, and magnesium are all required nutrients for the gardenia plant. The two most common nutrient deficiencies in these plants are iron and magnesium.

Yellow leaves with green tips often will be a sign of a magnesium deficiency, while yellow tips with green branch bases often signal an iron deficiency. You don’t want to plant near any foundations or concrete since this area could have a much higher pH than what the gardenia plant needs. If the pH is way too high, then your gardenia plant will not grow and likely will turn yellow within a matter of weeks.

How to Prevent Yellow Gardenia Leaves

There are several tips that you should follow if you want to prevent the yellow leaves on your gardenia plant. If this is your first time with a gardenia plant, you shouldn’t get discouraged if you notice the yellowing happening, but you should take immediate steps to correct the issues. The more you take proper care of your gardenia plant, the less likely you will be to see the leaves beginning to turn yellow.

1. Maintain Proper Soil Conditions

As we briefly mentioned, proper soil is important for the gardenia plant and it’s very easy for this plant to end up with nutrient deficiencies due to the pH of the soil being wrong. You should have your soil tested to ensure it falls within the 5 to 6.5 levels which are optimal for the plant to take in all of the vital nutrients. Adding peat moss, manure, or other organic matter regularly will ensure that the soil conditions remain healthy and safe for this plant.

2. Maintain Proper Humidity & Temperature

It’s important that the gardenia plant have the proper temperature and humidity levels to grow successfully. If the temperature is too low or too hot, then it could cause the leaves to begin to turn yellow, and eventually they will just fall off. Outdoors the gardenia plant will be the healthiest if it’s in a daytime temperature of around 65 to 70 degrees Fahrenheit.

The night temperature should be between 60 and 65 degrees Fahrenheit. Daily misting is also important because the gardenia plant will thrive in the higher humidity situations. You could also use a humidifier in certain situations to give the plant more humidity if needed or use moist pebbles underneath the plant.

3. Maintain Good Fertilize Balance

A good fertilizer balance is important for the gardenia plant to thrive. During growing season, which is March through October, you should fertilize every two to four weeks. You will need to use a fertilizer that acid-loving plants will enjoy and it should be diluted. November through February you should not be fertilizing the gardenia plant since this isn’t the growing season.

Sam Choan is the Founder of Organic Lesson. He started this site to share tips on using natural remedies at home when such options are available.

It seems the gardenia is quite the complicated plant. Sometimes it simply dies no matter what its caregiver does. In other cases, the plant thrives and blooms even though it’s ignored. If your gardenia’s leaves are starting to turn yellow, it could be a sign that your plant is in trouble.

The Gardenia’s Basic Needs

Gardenias can be grown indoors or outdoors. They produce beautiful flowers that emit a heavenly fragrance.

This plant prefers:

  • Acidic, well drained soil
  • Full sun to partial shade
  • High humidity
  • Proper ventilation

When these basic needs aren’t met, the plant begins to fail. Yellowing leaves are usually the first signal that something is wrong.

Reasons Gardenia Leaves Turn Yellow

The first thing you should do if your gardenia’s leaves begin to yellow is have some of the plant’s soil tested at your local nursery. This will reveal any possible nutritional deficiencies that could cause this problem. Here are some of the most common reasons for the yellowing.

Low on Magnesium

If your gardenia needs magnesium, this will cause the leaves to turn yellow. You can remedy this with a fertilizer high in magnesium, or you can add some Epsom salts to your soil. Mix one teaspoon to one gallon of water and apply every two to four weeks.This practice isn’t without its critics, however. Some say there is no evidence to prove that Epsom salts help gardenias or any other plants. One the other hand, countless gardeners swear by using this additive for their gardenias and roses. Give it a try for yourself and see if it helps.

Low on Iron or Manganese

Yellowing leaves can also be caused by insufficient levels of iron or manganese, and this is where a soil test becomes especially useful since the symptoms look the same. Using a balanced fertilizer will remedy this problem no matter which nutrient is missing.

You can also try applying a liquid iron spray directly to the foliage. Miracid is a great product for this problem.

  • Mix one teaspoon per gallon of water for indoor gardenias.
  • Mix one tablespoon per gallon of water for outdoor gardenias.
  • Apply the fertilizer every two to four weeks during the growing season.

Home remedies for acidifying the soil for gardenias include:

  • Diluted vinegar: Add one cup of vinegar to one gallon of water, and water the plant with this mix about once a month.
  • Pickle juice: Water the plant with pickle juice about once a month.
  • Used coffee grounds: Just dump your used coffee grounds under your plants each day. The worms love them too, which is great for your garden.

Poor Drainage

Poor drainage can also cause yellowing, but this is more of a problem with potted gardenias than those planted in the ground. While gardenias love humidity, they do not like to have soggy feet.

It’s also not a good idea to mist the leaves for humidity because this can lead to sooty mold on the leaves. The best way to provide humidity for your gardenia is to:

  • Create a tray of pebbles.
  • Fill the tray with water so the pebbles stick out just above the surface of the water.
  • Set the potted gardenias on top of the tray.

This will create humidity while the water evaporates, but it prevents the bottom of the pot from sitting in the water. Be sure the pot has drain holes in the bottom. That way, even if you must water daily, excess water will drain out the bottom so your gardenia won’t have soggy feet.

Crowding and Mold

Sometimes a gardenia’s leaves turn yellow on one side only. If that’s the case, note which side is turning yellow. Gardenias need good air flow around their leaves. If they’re planted too close to a building or another shrub, the side facing the object may develop yellow leaves. This may be a sign of a mold or a fungal problem in the early stages. The reduced airflow, combined with the plant’s proximity to the object and the resulting reduction of light in that area, can lead to the development of mold. You may need to trim back shrubs, trim the gardenia, or even move it to improve the situation.

Pests

Pests, such as aphids and mites, leave telltale signs in addition to yellow leaves. Look for:

  • Damage on the stems of the plant
  • Damage on the edges of the leaves
  • Webs on the plant that look like thin cotton threads

Watch for pests and treat your plant with an insecticide suitable for gardenias.

Incorrect Temperatures

Incorrect temperatures can cause leaves to turn yellow. The ideal temperature ranges for gardenias is 65 to 70 degrees during the day and 60 to 62 at night. It can be very difficult to keep these temperatures constant outside of a greenhouse environment, and wide fluctuations in temperature or cold spells will lead to yellowing.

Don’t Kill Your Plant with Kindness

Keep in mind that your plant’s oldest leaves will eventually turn yellow and fall off, and this is a perfectly normal part of growing gardenias. However, it’s important to try to keep your gardenia in the same location because these plants do not like being moved around or transplanted. Gardenias actually bloom better when they are slightly root-bound, and they’re often happiest when you just leave them alone without providing too much care.

QUESTION: We gave our gardenia a good feeding this spring, but much of the foliage is still yellow and leaves are dropping. The blossoms that do open are full of small insects. Can you cure these problems?

ANSWER: Some leaf drop is normal as gardenias renew their foliage during the spring months. But excessive leaf drop and the persistent yellowing after fertilizing normally is a sign of a magnesium deficiency.

Gardenias, along with roses, palms and podocarpus, need lots of magnesium. When the nutrient is in short supply, the older leaves turn yellow. Give the plant a boost (and maybe return some green to yellow leaves) by applying magnesium sulfate or Epsom salts. Mix a tablespoon of either in a gallon of water and sprinkle around the plants.

Thrips – about one-sixteenth of an inch long – love gardenias. The insects’ rasping, sucking mouth parts turn flowers brown. Control thrips by spraying Orthene on the flowers and developing buds. Thrips also love roses, which can be sprayed with Orthene as well.

Q: The floor under our palm is sticky. I think sap is dripping from the foliage. The plant looks great indoors, but I would like to eliminate the mess. What causes the stickiness?

A: Insects likely are making that sticky mess. Drippings usually are produced by scale insects or other piercing sucking types. The stickiness comes from the sap that oozes out the punctures and insect excreta.

Bathe small plants in soapy water to wash insects and sap away. Mix a tablespoon of mild dish detergent in a gallon of water and sponge down the foliage. Rinse the plant thoroughly, and when dry, return it indoors.

Try an insecticidal soap spray on larger plants left indoors. Several applications may be needed over a period of weeks. Use a damp cloth to wash off suspected insect clusters and sticky foliage.

Q: My 10-year-old crape myrtle tree has Spanish moss growing on it. A younger tree does not have the problem. How can I get rid of the moss?

A: Spanish moss seldom harms a tree, and some people feel it adds a Southern look to the landscape. Heavy accumulations may suggest the tree’s growth is slowing. This is normal as the tree ages, but most gardeners like to keep the crape myrtle vigorous.

Some pruning may be needed to stimulate new stems that will flower during the summer season. Cut back a few of the thicker limbs so side buds will sprout. Don’t cut all the limbs back to the same height. That gives the tree the unpleasant “hat rack” look.

Push new growth with feedings of 6-6-6 or similar fertilizer every six to eight weeks spring through early fall. Also apply a 3-to 4-inch layer of mulch and keep the soil moist.

Plenty of new foliage should shade the moss and keep it under control. Where removal is still desired, pull it from the tree or apply a copper-containing fungicide as labeled for use with crape myrtles. It acts as an herbicide, and the moss slowly will dislodge and drop from the tree.

Q: My neighbors help me with gardening advice, but they don’t always have the same answers. Tell me, what is a sucker? One neighbor said suckers come from the stems; another said they emerge near the blossoms. Which is correct?

A: Both neighbors are correct if they’re describing quick-growing limbs. In this case, a sucker is just a vigorous shoot no matter where it comes from. Suckers often form in areas where they are not needed and are pruned away. Some people incorrectly think that suckers will not form good limbs. When young, the growths may be attached to the tree weakly, but in time they will develop good, productive plant portions. If you need the limb, just support the sucker until the wood matures.

Suckers normally are eliminated when they arise from below grafts or at the base of trees. Here they are interfering with good growths and wasting the tree’s time. Vigorous shoots that crisscross among existing limbs may be removed.

Q: In spite of fertilizer and added minor nutrients, our Ruby Red grapefruit remains very yellow. It flowered and set fruit for the first time this year. Can we do something else to green up the tree?

A: Continued yellowing suggests the tree has a root or trunk problem. Check the tree trunk at the soil line. You may have a case of foot root where the bark is being damaged around the trunk which restricts water and nutrient uptake.

Other possible causes for yellowing include root rots, excessive watering and cold damage to trunk portions. Any of these can cause a tree to die. If you find wounds, clean away loose bark and spray with a copper fungicide as instructed for citrus. If cultural conditions are at fault, correct them immediately. Unfortunately, I expect the damage is extensive and your efforts will be in vain. The tree probably will have to be replaced.

Q: Help me settle a bet. I say a tree grows from the top, and you remove the lower limbs as needed. A friend says the tree grows from the roots, and the lower branches should not be removed since they will grow higher. Who is correct?

A: Trees grow taller, but not by pushing the limbs upward. All skyward growth comes from the ends of the branches. You win! Growth also occurs at the ends of the roots and just under the bark to increase trunk diameter. Once a limb has formed and the wood starts to harden, it never moves higher at the trunk.

Leave the lower limbs on the tree to feed the trunk until others grow to take their place. Horticulturists believe the first limbs with foliage play a major role in producing the food needed to grow strong trunks. Tom MacCubbin is the urban horticulturist at the Orange County Cooperative Extension Service, a division of the Institute of Food and Agricultural Sciencesat the University of Florida. Write to him in care of The Orlando Sentinel, P.O.Box 1100, Orlando, Fla. 32802-1100.

Gardenias

POSITION

Gardenias like a warm position. This is probably the single most important thing to remember when growing them in Melbourne. An east-to-north facing spot that captures sun till mid-afternoon is ideal. Against a brick wall or in a small courtyard that traps heat is also a good position. While they like heat, very hot afternoon sun can yellow leaves, so protection from the west (in summer only) is necessary. They are well-suited to being grown in pots and then can be easily moved around if there isn’t an ideal spot for them in the ground. Cold winter temperatures make leaves yellow and shed, particularly the older central leaves.

FEEDING

Gardenias like acid soil, so add plenty of compost or manure to the soil. Most potting mixes are usually slightly acidic. Feed twice a year as they come into bud in spring, and again after they finish flowering around December/January. Magnesium sulphate (Epsom Salts) helps to acidify the soil and prevent some yellowing of the leaves, as gardenias are a bit susceptible to magnesium deficiency. If new growth goes yellow to white, feed with chelated iron. Harry’s Gardenia Food is an excellent ertiliser specifically for Gardenias, to help keep them green and flowering. Results are impressive!

PRUNING

Shrubs should be pruned immediately after flowering and then fed with a high nitrogen fertiliser such as Harry’s Gardenia Food to promote autumn leaf growth. If they become very leggy, gardenias can be heavily pruned back to the old wood to make them bushy again. Mid spring is the best time for this, even though flowering may occur later in the summer than normal.

PROBLEMS

Aphids, thrips or mites can distort flower buds and new growth. Spraying with pyrethrum helps control these pests. Dropping of buds can be caused by lack of food (potash), but more commonly, it is due to cool or fluctuating temperatures in spring. Again, a warm spot is the best cure. Irregular watering can also be a factor. Scale can be controlled using products such as Pest Oil, Success or Eco Oil.

VARIETIES

Gardenia florida

Medium grower, smaller leaves and flowers than some varieties but the hardiest in Melbourne.

Gardenia radicans

Small-leafed, horizontal, rockery gardenia, good for pots, even hanging baskets. Needs warm spot.

Gardenia magnifica

(Golden Magic) Taller growing, more spectacular varieties with big glossy leaves and larger flowers. A bit more temperature-sensitive in Melbourne.

Gardenia thunbergia Tree gardenia, medium shrub, quite hardy in Melbourne. Single tubular flowers, very beautiful but difficult to obtain. Specimen in Burnley Gardens and a hedge on the east side of the Botanic Gardens.

YELLOWING LEAVES

Occurs naturally through the colder months, so don’t worry in mid to late winter. Gardenias sometimes take a few years to settle into a new position, so persevere. Nitrogen & magnesium (Epsom Salts) in spring helps to stop yellowing. They are heavy feeders when setting bud, so apply Harry’s Gardenia Food for best results. A warm spot is the best cure for yellowing leaves. Feed with a liquid fertiliser every 4-6 weeks (even through winter) to help to avoid yellow leaves.

Gardenia Love by ClaraDon

TheGardenLady received this question from Mable.

I was told to dilute vinegar in water and use that on gardenia’s with yellowing leaves. Do you agree?

Gardenias by Jim-AR

Gardenias love acidic soil. If they are indoors, gardenias should be planted in an acidic soil that has a pH level of 4.5 to 5.5. If growing outdoors, have the soil tested before planting the gardenia to see that it has the right pH. See here.

Gardenias can have a host of problems. They are difficult plants to raise, especially when indoors. They suffer from a number of problems, yellow leaves just being one of the problems. Of three common things that can cause yellowing leaves is improper watering, too low light and the plants needing acid fertilizer.

Overwatering can cause the leaves to yellow.

The gardenia plant should be fertilized monthly between April and November with an acid fertilizer especially if you are using well or tap water. Some people recommend using distilled water because it is not alkaline. See here.

It is fine to use diluted vinegar on your gardenias. The Vinegar Institute recommends using diluted vinegar on gardenias (also azaleas and rhododendrons) in hard water areas at a rate of 1 cup of vinegar to a gallon of tap water (see here). The vinegar will help to release iron in the soil.

On Garden web, a reader has suggested another solution to get iron into your plant that she says has been proven successful for her plant.

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Filed under Acid Loving Plants, Gardenia

‘Dear Dr. Kris
I have several Gardenias doing wonderfully, however, the one I have in front has constant yellowing leaves. I have fertilized and added iron. Still had more leaves yellowing so added iron again. This has not solved the problem. Did I possibly add too much or still not enough? Or is there something else wrong? I have it in mostly morning sun followed by some afternoon shade. Do you have any suggestions or advice? Jim Williams, Seminyak’

Learning all of the details of how to grow gardenia really well is worth the trouble. The plant’s blooms produce a scent that most gardeners find captivating. The flowers are well known for their fragrance as well as their beauty. Obviously you need healthy foliage first, if you are going to have healthy blooms of flowers!

Yellow leaves on a gardenia bush indicate chlorosis, or chlorophyll deficiency. (Chlorophyll is the chemical that makes the leaves green and helps plants with photosynthesis). The problem is easy to diagnose, though determining the underlying cause of the chlorosis usually requires some trial and error to solve the problem. For the gardenia or any other plant for that matter, the chlorosis could be caused by an improper pH level in the soil, poor drainage or ventilation, insufficient soil nutrients, unhealthy roots, or a combination of all of these factors.

The basic needs of the gardenia are an acidic soil which is also well drained, high humidity, full sun to partial shade and proper ventilation. When these basic needs aren’t catered for, the plant begins to stress and premature yellowing of the leaves is usually the first sign that something is wrong.

Soil pH – This is a very important factor for gardenia health. The first thing you should do if your gardenia’s leaves begin to yellow is to test the soil pH. These plants are acid loving, so when the soil gets too alkaline, it will easily cause chlorosis and the leaves will turn yellow.

Gardenias need an acidic soil of around pH 5.0-6.5, if the pH is higher than 7.0 the soil is far too alkaline for them to thrive, and the soil will need to be amended or completely changed. The pH level affects the chemical makeup of the soil, it will determine the levels of nutrient that are available to the plant, and it is very important for successful gardening. Depending on the type of plant, some prefer an alkaline soil, but for the gardenia an acidic soil is definitely the requirement. When the pH level is imbalanced according to the plants needs they cannot absorb the minerals they need, and this a major cause of chlorosis.

Home remedies for acidifying the soil for gardenias include:
Diluted vinegar: Add 100 mls of vinegar per litre of water, and water the plant with this mix about once a month. Used coffee grounds: Dump your used coffee grounds or tea leaves under your plants each day. The worms and microbes love them too, which is great for your garden.

Gardenias are an acid loving plant, so they should not be planted close to concrete, which is a highly alkaline material. Water run-off from concrete will create nutrient problems that can lead to chlorosis and yellow leaves. The different remedies gardeners recommend for gardenias, such as giving them magnesium, applying cornmeal around the roots, or adding compost, all work by adjusting the pH level in the soil. Thus, it is important to determine the pH level of the soil before applying any treatment.

Drainage – Though gardenias need moist soil, yellowing leaves can also be caused by over watering or even under watering. Gardenias need consistent regular moisture to stay green and healthy. Good drainage is also critical. Whilst gardenias love humidity, they do not like to have wet feet. Wet roots start to rot, affecting water and nutrient absorption. You can grow them in full sunlight so long as the drainage is perfect. The soil porosity should be such that even if it were watered every day, it would never be soggy or boggy. If the soil is the problem then aerate and add compost to improve the drainage, or if it is possible move the entire plant into a new well drained soil mix. The reason some folks gardenias survive with little care, even neglect is because their drainage is perfect.

Ventilation – Gardenias need adequate air circulation around their leaves. If they’re planted too close to a building or another shrub, they may develop yellow leaves. This may be a sign of a fungal problem. The reduced air circulation, combined with the plant’s proximity to other objects and the resulting reduction of light in that area, can lead to the development of fungus. You may need to trim back the surrounding shrubs or trees, trim the gardenia, or even move the entire plant to improve the situation.

Nutrients – It could be low on iron or manganese. By using a balanced fertilizer you will remedy this problem no matter which nutrient is missing. Choose from fertilizers such as 6-6-6 or 10-10-10. Home remedies to nutrient deficiency – you could try adding epsom salts dissolved in water or sprinkle cornmeal (not self-raising) around the base of the plant a few times a year. It will give the plant a boost and reduce yellowing leaves.

Pests – Pests, such as aphids and mites can cause the leaves to yellow. Look for damage on the leaf tips and edges, the stems and small webs on the plant that look like cotton threads. Watch out for pests and if you need to treat your plant try with an organic insecticide.

Finally, remember that some yellowing on older leaves is normal, your plant’s oldest leaves will eventually turn yellow and fall off. This is a perfectly normal part of growing gardenias it is when most of your plant is full of yellow leaves that you really have a problem!

Dr. Kris
Garden Doctor
Contact: [email protected]

Copyright © 2013 Dr. Kris

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