Frequently Asked Questions: Plants

My azalea leaves are turning yellow. What is the problem?

When the new growth of azaleas turns yellow, it usually indicates an iron deficiency. Azaleas prefer soils which have an acid pH because certain nutrients, including iron, are more available at lower pH values. Yellow leaves on azaleas can indicate an iron deficiency because (1) not enough iron is present in the soil for the azaleas to utilize, or (2) the pH is not low enough to release the iron that is present. Azalea "special" fertilizer contains soil acidifiers which temporarily lower (acidify) the soil pH. Applications of iron sulfate or iron chelate will also correct iron deficiencies. Coastal soils are naturally alkaline and it is nearly impossible to permanently adjust a naturally alkaline soil. Therefore, azaleas and other acid loving plants should not be selected for that site. Yellowing leaves on azaleas can also be an indication of a root rot fungus due to poor soil drainage; planting too deep (see question 7 below); or poor establishment (see question 3 below).

When is the best time to plant or transplant my plants?

Container-grown plants can be transplanted any time of the year. The critical factor is keeping the soil moist to prevent the root ball from drying out. To dig and move hardy plants that are growing in the landscape, it is best to wait until the dormant period between December and February. If the plant is considered tender to cold, it is best to delay planting or transplanting until after cold weather passes (March/April).

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I recently planted some azaleas and have watered faithfully, but the leaves are turning brown and dry. What is the problem?

When planting azaleas, it is important to wet the root ball and gently loosen and separate the roots before planting. This is of critical importance because of the very fibrous root system and the high peat soil mix in which these plants are grown. Prepare the planting bed (not just the planting hole) by adding lots of peat or compost. Mulch well and keep the soil moist until the azaleas are well established.

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How should I protect my tender plants from freezing temperatures?

The most practical way for homeowners to protect their plants is to cover them. Cardboard boxes, blankets, newspapers, plastic, etc. can be used. The cover must extend all the way to the ground to trap the heat given off from the soil. Homeowners should not try to use sprinkler systems to protect plants. Home irrigation systems cannot apply enough water fast enough to do the job. Instead, more harm than good is usually done.

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Why didn't my poinsettia bloom for Christmas?

This can result from a couple of problems. First, poinsettias should not be pruned after September 10th. Flower buds are set sometime between September 10th and October 10th. Pruning anything within this period could remove those initiated flower buds. Flower initiation in poinsettias is stimulated by long nights and any light interruption at nights can reduce or delay flowering. Light from a street light, interior light, or headlights from a passing car is sufficient to interfere with the flowering process.

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Should I mulch my plants?

Mulching is considered a beneficial practice for all ornamental plants. Mulching conserves soil moisture, insulates the soil (keeps it cooler in summer and warmer in winter) and suppresses weeds. Organic mulches such as shredded wood, pine needles or oak leaves are preferred to inorganic mulches such as pebbles and stone. The desired depth of the mulch is 2 to 3 inches after settling. The area immediately around the stem of the plant should be left free of mulch.

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How deep should I plant my shrubs and trees when planting or transplanting?

Never transplant ornamental trees and shrubs any deeper than they were planted in the container. Dig the planting hole twice as large as the root ball, but no deeper. There is no benefit from back fill amendments, unless the entire planting bed is amended.

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When should I prune my plants? Is there a general rule?

Pruning depends on plant growth and blooming habit. In general, shrubs and trees which bloom during the winter and spring should be pruned immediately after they flower. This type of plant sets its flower buds in late summer, so do not prune after August. Shrubs which bloom during the summer and fall produce flowers on the current season's growth. Therefore, the best time for pruning would be in late winter or very early spring before new growth starts to develop. Evergreen shrubs and trees which are grown primarily for their foliage may be pruned any time. Shrubs and trees which lose their leaves during the winter months may be pruned while bare of leaves.

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Every fall the leaves on my gardenia and hibiscus shrubs turn yellow and drop. What could cause this?

In fall and spring, when night temperatures are cool and days are warm, it is not uncommon for some leaves to turn yellow and drop. There is no treatment or prevention for this. If yellow leaves and leaf drop occur at other times of the year, it is a sign of stress resulting from water stress, improper fertilization, root disorders, nematodes, or misuse of chemicals.

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The flower buds on my hibiscus and gardenia plant drop before they open. What could the problem be?

Bud drop is often a problem with both of these plants and can indicate an insect problem, cultural/environmental problem, or a characteristic of that variety. Insects called thrips can damage the unopened bud. These may go undetected until considerable damage has occurred and the buds drop. Too much or too little fertilizer and/or water can stress the plant resulting in bud drop. Nematodes can attack the root system reducing the plant's ability to take up water and nutrients. Some varieties of hibiscus, especially doubles, are characterized by premature bud drop. Some varieties bloom well during one period of the year and consistently drop their buds at all other times.

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