Pruning Azaleas and other Shrubs

Don't prune for the sake of pruning

Brian Jervis: Ask a Master Gardener

Saturday, May 28, 2016

Q: How should I prune my azaleas? — Tim, Tulsa

A: Before you prune azaleas, or any plant, ask yourself what the reason is for pruning. If there is no good reason, don’t prune just for the sake of pruning. Inappropriate pruning abounds in area landscapes, especially in crape myrtles.

Pruning trees and shrubs is best done in winter, especially late winter. The exception to this is spring-blooming shrubs, which should be pruned after blooming is completed. The only reason to prune at that time, rather than winter, is to preserve the buds that form blossoms in spring. Like most spring-blooming plants, azaleas produce flower buds from mid-summer into fall of the previous year. If pruned any time after buds are formed, during summer, fall or winter, spring blossoms will be lost.

There are several legitimate indications for pruning azaleas or any shrub. One is to control size or alter shape and appearance. However, if the shrub is too large for an area and must be cut back yearly, thought should be given to removing the plant and getting a smaller cultivar.

Another reason to prune is to remove any dead or damaged limbs; this should be done anytime they are noticed. Also, removal of any overcrowded, crossing or rubbing limbs, especially those inside the shrub, will improve air flow, improve health and lessen the likelihood of diseases.

For azaleas that are old and overgrown, “rejuvenation pruning” may be the way to go. This process may need to be done over a few years, but it can rehabilitate an old favorite shrub. It may be done before new growth starts in spring with the understanding blossoms will be lost. The process is to remove about a third of the oldest largest stems back to a few inches from the ground. The younger stems will then have more growth and eventually more blossoms.

Then remove another third of the older stems yearly over the following two years and the shrub will then be “rejuvenated.”

One thing that is best avoided when pruning azaleas is using the hedge trimmers to try to shape them into a boxy hedge. Far better results are obtained by using hand clippers and pruning one branch at a time, creating a form that seems natural, as well as achieving your pruning goals.

All of the deciduous summer-blooming shrubs such as abelia, Rose-of-Sharon and crape myrtles are best pruned in late winter or early spring before summer buds form. The broadleaved evergreen shrubs like camellia, hollies, boxwoods, nandina and photinas should also be pruned in late winter and early spring.

Needled evergreens like pines and arbor vitae usually do not need pruning. Be careful about pruning these plants. You might refer to the OSU fact sheet HLA-6409, “Pruning Ornamental Trees and Shrubs,” for information about pruning these and all plants. It is available from OSU or from the Tulsa Master Gardener’s website, tulsamastergardeners.org.

For more information or to ask a question about gardening, contact the Master Gardeners at 918-746-3701 from 9 a.m.-4 p.m.

Garden tips

Powdery mildew Alert

With springtime temperatures and wet weather, this fungus infection is widespread now. Master Gardeners are getting daily calls about the disease on a host of plants.

The infection can involve trees and shrubs, such as crapemyrtles and lilacs, as well as many ornamental flowers. Most garden vegetables are susceptible to it, especially cucumbers.

The disease infects leaves, where it typically produces a whitish powdery coating. In some plants, the fungus causes only yellow spots, rather than powdery discoloration. The infected leaves usually die when infected.

To treat the infection, OSU recommends a fungicide, chlorothalanil, found in Ortho Garden Disease control, as well as other brands. This fungicide is effective, but it only prevents new infection and cannot eliminate established disease. Leaves with infection should be removed, if possible, and placed in the trash.

Organic treatments may include horticultural oils, fungicides based on copper or sulfur compounds and potassium bicarbonate solutions. These are not as effective as chlorothalanil and are mainly used as a preventative in susceptible plants.

Also, if you are able to increase air circulation and sun exposure of the plants, this significantly reduces the incidence of the disease. The ultimate control is to plant those cultivars of plants that have shown resistance to the disease.

Causes of Yellow Plant Leaves

Nutrients, environment are common causes for yellow leaves

Bill Sevier:  Ask a Master Gardener

Saturday, May 21, 2016

Q: My azaleas have some yellowing of their leaves and did not bloom well. Any suggestions? R. T., Tulsa

A: There are several factors that can cause yellow leaves and poor performance in all plants. Although various insects and diseases may produce this, far and away the most common causes fall into the nutrient and environmental category.

When planting anything, it is best to know what type of growing conditions the plant prefers and should be coupled with a recent soil test. If there are any mismatches, they should be corrected before planting.

Azaleas must have acid soil (low pH) to absorb iron and other nutrients. If the soil is not acidic enough, the plant cannot absorb iron and iron chlorosis develops, as seen in the photograph. With iron deficiency, the leaves are yellow except for the veins, which remain green. This is called “interveinal chlorosis.”

Another nutritional deficiency that produces yellow leaves is lack of nitrogen. Among the several nutrients needed by all plants, nitrogen is used in the largest amounts and is the major component of most commercial fertilizers.

Nitrogen deficiency causes the leaves on the lower part of the plant to turn yellow before the upper leaves are involved; while iron chlorosis tends to affect all leaves similarly. A soil test will identify nitrogen deficiency and most any type of organic or commercial fertilizer will correct it.

Environmental changes involving temperature, light and water are common causes of yellow leaves in all types of plants, including houseplants. Houseplants often develop and shed yellow leaves when being moved from indoors to outside or vice versa. The yellow leaves are an adaptation to change in light and temperature. It has no significant effect on the plants health.

This time of year too much water in the soil commonly causes yellowing of leaves in shrubs, ornamentals and in the vegetable garden. This is due to water forcing out oxygen from the soil which causes the roots to suffocate. If the roots cannot function, the plant cannot obtain adequate amounts of not only oxygen, but water and nutrients. This produces yellow leaves and poor health of the plant. Over watering houseplants produces a similar condition and is probably the number one cause of yellowing of houseplant leaves.

The other causes of yellow leaves such as disease and insect pests, are often evident from the appearance of the leaves. However, root diseases such as root rot, acts exactly like overly wet soil and causes the roots lose their absorbing ability.

It sometime is confusing when evaluating a yellow leaf with fungal spots as to which came first, the yellowness due to an environmental condition and the fungal infection being an opportunist, or the fungus being the primary problem.

The Tulsa Master Gardeners can help with all these problems. Call 918-746-3701 or come by with photos or samples to the OSU Extension Office at 4116 E. 15th St. at the fairgrounds, gate 6.

---

For more information or to ask a question about gardening, contact the Master Gardeners at 918-746-3701 from 9 a.m.-4 p.m.

Garden tips

§  Clean out water garden and prepare for season. Divide and re-pot water garden plants. Begin feeding fish when water temperatures are higher than 50 degrees.

§  Plant warm-season vegetable crops such as watermelon, cantaloupe, cucumber, eggplant, okra, sweet potatoes, etc., now.

§  Late May is the best time to control borers in the orchard. Contact OSU Tulsa Master Gardeners for fruit tree spray recommendations.

§  After all the recent rains, you should let soils drain from soggy to a moist condition. Spading or tilling wet soil will cause collapse of small air spaces, producing long-term damage.

Dealing With Moles and Gophers

Moles, gophers are common landscape pests

Brian Jervis: Ask a Master Gardener

Saturday, May 14, 2016

Q: Something is tearing up my yard. I can’t tell if it’s moles or gophers. What should I do? M.S., Tulsa

A: Moles and gophers are recognized pests in the landscape and can cause significant damage but in different ways. Likewise, the suggestions for control of the two are similar but different.

Moles are insectivores and only eat insects, mainly earthworms, while gophers are rodents and eat plant roots. Moles do not eat plant roots.

Moles have superficial tunnels easily seen, and they rarely make dirt mounds. Gophers also have tunnels but are too deep to be seen. They excavate mounds of dirt, usually a foot or more in diameter typically kidney shaped with a small depression on the flat side. This depression is usually over the end of a deep side tunnel.

So if you can see tunnels, you have moles. If you have several large fan-shaped fresh dirt mounds, you have gophers.

Best control of the two pests is by traps and poison baits, but the types of traps and baits are different for each.

For helpful information about mole control, look online for the University of Arkansas fact sheet “Controlling the Eastern Mole.” For gopher control advice, obtain OSU fact sheet “Controlling Pocket Gophers.” Both have useful discussions about the behaviors of both pests, which types of traps and baits to use and how to use them.

For successful trapping or baiting of moles, one must identify an active tunnel. The visible tunnels in the lawn are usually made by only 2-3 moles. Most of the tunnels are feeding tunnels used only one time. To identify a frequently used traveling tunnel, poke a broomstick-sized hole in the tunnel or compress a section and check back in 1-2 days to see if it is repaired. If so, that is the tunnel that should be used for a trap or poison bait.

Several types of useful mole traps are set above ground over the tunnels. These traps are effective if used according to directions and used with patience and persistence.

Garden centers and hardware stores have a variety of products for mole control, but studies have shown that, other than traps, the best control is with a poison gel worm such as Tomcat Mole Killer and several other brands. These are placed in one of the previously identified active tunnels.

While mole traps are set on top of the ground, to set gopher traps one must dig down to the tunnel, which may be at a depth of a foot or more. Usually two traps at a time are set, one at each end of the excavated tunnel.

Poison baits for gophers are usually in the form of grain and are poured through a pipe into a gopher tunnel. Tunnels are identified for bait application without digging, by probing into the soil adjacent to the mounds.

All these traps and poisons have their hazards and risks to children, pets and other animals. Read the above references and then follow the labeled directions of all products.

Garden tips

§  Nutsedge weeds are emerging now. Post-emergent treatments are best applied for the first time this month. Nutsedge control requires specific herbicides found in Image, Sedgehammer and others; standard broad-leaved post-emergent herbicides are not effective. Contact the OSU Tulsa County Master Gardeners for recommendations.

§  Plant summer bulbs such as cannas, dahlias, elephant ear, caladiums and gladiolus.

§  Apples and other fruit need thinning for best production. Apples form buds for the next year’s crops in June, and if the small fruit is not thinned in the current year, next year’s crop will be small. Thinning also produces larger fruit. Thin to one apple every 4 inches.

§  Remember, working wet soil will cause significant damage to the soil structure. Give it time to drain from recent rains before tilling. Damage from tilling while wet may last a long time.

Organic Pesticides

Organic pesticides can still be harmful

Bill Sevier: Ask a Master Gardener

Saturday, May 7, 2016

Q: Can organic insecticides be harmful? I always presumed they were not. R.D., Tulsa.

A: For the most part, all pesticides have the potential to be harmful. Organic pesticides are ones approved by the USDA’s National Organic Program, a division of the USDA. This agency evaluates and approves all aspects of organic food production.

Generally speaking, organic pesticides are those derived from plants and minerals “naturally” as opposed to those man-made (synthetic pesticides). However, there is overlap. Some organic pesticides are synthetic and some botanical and mineral products are not certified for organic use.

Organics are selected for reduced toxicity to other plant and animal life and also for a short duration in the environment. Organic farming principles also emphasizes improving soil health, use of pest-resistant plant varieties and improving overall growing conditions before using any pesticide.

The federal regulations concerning what is approved and what is not is an eye-crossing experience in an attempt to understand. However, the following are some of the organic pesticides (mainly insecticides) approved and commonly used by organic gardeners.

Bacillus thuringiensis (Bt) is a bacterium safe for animals, fish and beneficial insects. There are several varieties. “Kurstaki” is effective for most caterpillars. “Israelensis” is used in water to kill mosquito larvae and others are used for types of beetles. Bt is widely used on vegetables by homeowners and in agriculture.

Horticultural soap is another effective and safe pesticide. Not being found in nature, it is “synthetic” but is classified as organic. It is an excellent choice for many of the insects in vegetable and other gardens.

Horticultural oils are also effective for a wide range of insects. These oils come from either vegetable or petroleum sources. They smother insects and are safe to use in most garden areas.

Neem Oil is a horticultural oil but is a little different from the others. It comes from seeds of the Neem tree grown mainly in India, where it has been used for many years in medicines and cosmetics. The raw oily seed extract has a number of chemicals with pesticide properties. These are usually extracted, and the pure oil is sold in garden centers.

Azadirachtin is the main chemical extracted from the original neem oil. It is safe and effective for many insects. It has an effect of altering the feeding behavior and growth of insects.

Pyrethrin is an insecticide coming from certain varieties of chrysanthemums. It has a wide range of activity and deteriorates rapidly after sprayed.

Spinosad is an extremely useful insecticide derived from a type of soil bacteria. It can be toxic to bees but seems to be moderately safe if used when bees are not present. Do not use when plants are in flower.

There are many other approved organic pesticides not listed. As always, if you use any pesticide, the labeled directions must be followed. Any pesticide toxic to bees should only be used in the early morning or late in the day, when bees are back to their hives.

Garden tips

§  Prune and feed all of the spring-blooming shrubs, such as azaleas and forsythia immediately after blooming, if needed. Azaleas need less fertilizer than many shrubs and often a yearly addition of mulch, as it decays, it will add all the nutrients they need.

§  Cool-season lawns — tall fescue and bluegrass — can be fertilized again if you did not fertilize in March and April, do so now. Do not fertilize these grasses in summer.

§  Seeding and sodding of warm-season grasses such as bermudagrass, Buffalograss and zoysiagrass is best performed in mid-May through the end of June. The soil temperatures are warm enough for germination and growth. These grasses need a long summer growing season to promote winter hardiness.

Composting Yard Waste Basics

Turning waste into compost

Brian Jervis: Ask a Master Gardener Saturday,

April 30, 2016

Q: I would like to compost my grass clippings and some of the other material from my gardens, but I am not sure how to get started. Suggestions? Jim, Broken Arrow.

A: Many people dutifully recycle paper and other approved wastes by placing them into the city's recycle bins but send their yard wastes to be burned — wastes that are beneficial if recycled. These materials are best added to a compost pile, and when fully composted, they produce superb additions to garden beds, either tilled in or used as a mulch.

Limitations to composting may be lack of information about the process, space for a compost bin and a determination to recycle.

The OSU fact sheet “Backyard Composting in Oklahoma” will supply the information needed to get started. This fact sheet explains the composting process, including what can be composted, how to build a bin and what can go wrong. There are also many excellent websites on composting, including the city of Tulsa’s website.

One first needs to identify a space that can be devoted to a bin. Many materials are available to build a bin, such as various types of stone, treated lumber, old wood pallets and wire fencing. These structures keep the materials together. However, some people simply make a large pile of materials to compost, although effort must be made to keep it contained.

Several versions of drums are used for composting. These may be bought or made from a plastic trash can. The commercial ones are expensive but work well and are tidy. Cornell University Extension's website has a list of suppliers for these drum composters.

It has been shown that one needs a combination of two types of materials for composting. These consist of brown materials, which are high in carbon, and green wastes, which contain the nutrient nitrogen. The browns are typically fallen leaves, straw, paper and wood wastes — chips and sawdust. The greens are often lawn clippings, green garden trimmings and kitchen scraps. If a pile has only brown material, a substitute for greens is a handful of nitrogen fertilizer.

Animal manures may also be added but only from plant-eating animals (herbivores). Cat, dog and human wastes should not be used. Also, one should not add any dairy products or fatty wastes from the kitchen.

The composting process is performed by many different types of bacteria and fungi. They decompose, or break down, the materials into garden-friendly organic matter, which is compost. These microorganisms need oxygen, water and nutrients to do their job. Done properly, the decaying process produces heat, and the core temperature may reach 140 degrees and will kill many, but not all, of any disease and insect pests. It is important to keep the pile wet and turned often. The more it is turned, the more oxygen is able to penetrate the pile and the faster it will compost.

Garden tips

§  After moving potted plants from inside to outdoors, irrigate the pots with 2-3 pot volumes of water to remove salts that may have accumulated from fertilizers.

§  Spring-blooming bulbs are best fertilized in fall and late winter when leaves emerge. After blooming, they go dormant and cannot use fertilizer applied at that time.

§  When Bermuda and Zoysia lawns are fully green, begin applying fertilizer. Bermuda grass will benefit from 2 to 5 pounds of nitrogen fertilizer per 1000 square feet in divided applications over the summer. Zoysia lawns need about half that amount. Don’t use a phosphorus-containing fertilizer unless a soil test indicates a need.