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March Gardening Topics


  • Applying Dormant Oils for Winter Insect Control - David Hillock, Consumer Horticulturist

    For home gardeners and fruit growers an important insect management tool is dormant oil application. Dormant oil is a refined petroleum product formulated for use on trees and shrubs. This refers to the time of application which should be late winter or early spring. Applications should be made when temperatures are above freezing and before bud swell and bud break before new growth forms. Ideal temps are between 40 and 70 degrees.


    If applied too early, before hardening off, the trees can sustain winter injury. Also, if the temperature is too low the oil will not mix well in solution, and you will not get adequate coverage needed to control overwintering insects. Late February through March should be a good time to make these applications, although check the weather and make sure there will not be any freezing temperatures or rain for a few days after applications.


    Dormant oils control scale insects, aphids, and mites that are overwintering on the trees. The oil must be applied with enough water to get thorough coverage (read label recommendations). Coverage is very important so that the spray can reach in between the cracks and crevices of the bark where many insects hide. The oil coats the insects and fills the spiracles. Insects use their spiracles to breathe so when they are blocked, they smother. Dormant oils will suppress insects by killing overwintering adults and eggs which will slow the seasonal build up in the spring. This is well worth the extra time. Some insects controlled by dormant oils include aphids, scales, and mites.


    Applications should be made to apples, pear, plum, pecan and crabapples. Peaches, nectarines, apricots and plums often do not require dormant oil sprays, but if certain insect pests have been an issue in the past it could be beneficial. Dormant oils can also be beneficial for shade trees and woody ornamentals. Consult your label before application to make sure the plant is listed. Some plants are sensitive to dormant oil applications.


    Precautions: Do not apply too early or too late. Avoid temperature extremes. Avoid using on plants that are oil sensitive. There will be a list on the label.


    Dormant oils will kill annual flowers; do not make applications to trees close to annuals. Do not apply in combination with sulfur containing pesticides such as captan. This will cause plant injury.


    Benefits far outweigh the negatives. It is inexpensive and less toxic than other sprays used to control these pests with little toxicity to birds and mammals. This will provide your plants with a jump start into spring.


    Dormant oils can be purchased at any garden center and are relatively inexpensive. Remember to read the label and follow all label recommendations!

  • Pruning Roses - David Hillock, Consumer Horticulturist

    Rose plants need pruning to tidy up their appearance; control size; and improve their vigor, growing habits and bloom. Pruning methods vary according to the type of rose plant. To keep them in bounds, spring pruning usually is more drastic. Prune about 3 to 4 weeks before the average date of the last killing frost in your area. In most of Oklahoma that would be around the 15th of March. An exception to this rule involves climbing roses, which need to be pruned after flowering in early spring.


    Probably no other aspect of growing roses has aroused as many questions as has the subject of when and how to prune roses. By following a few simple rules, you can improve their appearance and vigor and control the quality and quantity of the flowers. Some fundamental practices of pruning roses correctly in all gardens, regardless of type, are: 1) remove any canes that have been damaged by insects, diseases or storms; 2) remove one of two canes which may be rubbing one another; and 3) remove canes that are spindly or smaller in diameter than the size of a pencil. After pruning, according to these general recommendations, cut hybrid teas, floribundas, grandifloras and polyanthas back to 12 inches for large flowers and 18 to 24 inches for many smaller sized flowers.


    Climbing roses generally are pruned to renew plant vigor by removing the old canes since the most productive and finest blooms on climbers are produced on canes that arise from the bottom of the plant the previous year. These newer canes produce more desirable growth and flowers. Since the canes may become quite long, it is necessary to prune them back so they are maintained in the desirable area.


    Old fashion or antique roses require much less pruning than modern roses. Left unpruned old fashion roses will naturally obtain a rounded shrub shape. Pruning of these roses should be confined to some shaping of the plant, removal of damaged branches, and judicious trimming back to encourage growth.


    On all roses, consider the cutting of the flowers as a form of pruning. When gathering roses, always leave at least two sets of leaves on the branch from which you cut the flower to insure plant vigor. When removing faded, spent flowers, cut only as far as the first five-leaflet leaf. Make cuts on the ends of branches at 45-degree angles just slightly above an outside facing bud with the lowest point on the side opposite the bud, but not below the bud itself. Never leave stubs when removing branches, since these die and can cause problems on the plant later. Always remove branches by cutting to a lateral branch or bud, or back to the base of the rose plant.


    For more information on growing roses in Oklahoma see fact sheet HLA-6403 Roses in Oklahoma. 

  • Control Peach and nectarine Leaf Curl Now! - David Hillock, Consumer Horticulturist

    It is common to get calls in early summer by homeowners wanting to know what is wrong with their peach or nectarine tree.  Infected leaves pucker, become deformed, and turn yellow or reddish-brown. Unfortunately, by that time, when symptoms are most evident, it is too late to spray anything. Leaf Curl is the culprit and is one of the most encountered diseases in unsprayed orchards and home yards during cold, wet springs. Diseased leaves eventually wither and fall from the trees. Although new leaves emerge from dormant buds, their growth requirements reduce yield and may weaken the trees.


    To prevent leaf curl disease, spray peaches and nectarines with a fungicide before bud swell (EPP-7319 Home Tree Fruit Production and Pest Management). Apply when the trees are dormant and temperatures are above 40 degrees F, usually mid-February through March depending on weather and location in the state. Bordeaux mixtures, copper flowable fungicides, chlorothalonil, and lime-sulfur sprays are commonly used for control of leaf curl.

  • Growing Seedlings - David Hillock, Consumer Horticulturist

    Buying transplants in the spring from local garden centers and nurseries is an easy way to get a garden started, but if you are up for a challenge and want more variety when it comes to cultivar selection you might try starting your own plants indoors from seed. After seeds have germinated, they must be promptly given the best possible growing conditions to ensure stocky vigorous plants for outdoor planting. Cultural requirements must be considered carefully.


    Light. Seedlings must receive bright light promptly after germination. Place them in a bright south-facing window if possible. If a large, bright window is not available, place the flats or pots under fluorescent lights. A fixture containing two 40-watt fluorescent tubes is adequate. Place the seedlings about 6 inches from the tubes and keep lights on for 14 to 16 hours each day. As seedlings grow, the lights may need to be raised to prevent leaf burn as seedlings touch the tubes.


    Plants need some red and infrared radiation. Since this is not supplied by common fluorescent tubes, additional light from incandescent lamps or windows is necessary. If this cannot be given, use a fluorescent tube specially designed for plant growing. These are available under a variety of trade names. LED lights specially designed for growing plants are also available now.


    Temperature. Most annual plants and vegetables prefer nighttime temperatures between 60- and 65-degrees F. Day temperatures may run about 10 degrees higher. If temperatures are warmer than this, leggy plants result. Cool-season vegetable crops and a few flowers prefer night temperatures no higher than 55 degrees F and day temperatures near 65 degrees F. An unused bedroom, basement or sun porch is often a good location.


    Moisture. Good humidity is an asset for producing good plants. A humidifier may be used, or shallow pans of gravel filled with water may be placed as close to the growing area as possible. Flats should be always kept moist, but never soggy. Allow drying between watering, but don’t allow seedlings to wilt at any time.


    Fertilization. Seedlings will need some fertilization for best development. Those in totally artificial mixes need prompt and regular fertilization. Use a soluble house plant fertilizer as sold in garden centers and nurseries. Young, tender seedlings are easily damaged by too much fertilizer. Apply fertilizer at about half the recommended strength a few days after seedlings have germinated. After that, fertilize at two-week intervals with the dilution recommended by the manufacturer. Water and fertilize carefully.


    “Damping off”. When seedlings fall over at the ground level, they are being attacked by a fungus disease known as “damping off”. If only a few seedlings are attacked, dig out and discard the infected plants and soil. Drench the entire soil mass with a fungicide if the disease is scattered throughout the flat or pot. This may not provide complete control. High temperature, poor light, or excess moisture stimulate spread of the disease by weakening plants to make them more susceptible to it. Best control is cleanliness and prompt action when the disease appears.

  • Irrigation System Maintenance: Spring Start Up - David Hillock, Consumer Horticulturist

    Now is a good time to prepare your irrigation system for the season. Before turning it on make a visual inspection of the sprinkler heads. Check for broken heads or covered up heads; free heads, make height adjustments, and be sure spray heads are still properly orientated. Check all valve boxes for rodent nests and debris.


    Make sure there is power to the controller and set stations for proper run times. Turn the main water source on slowly to fill the system. If you have manual drain valves, leave them open to allow air to escape as the pipes fill with water; when water starts coming out the drain valves, close them.


    Turn on each irrigation zone one at a time or set your controller to run through each zone using a test cycle setting. If choosing to run a test cycle of each zone, set a time limit long enough to observe each zone and mark needed repairs, about three minutes.


    While each zone is running, walk through the yard and check each sprinkler head, noting any that require attention. Flag or mark problems to make them easier to identify when making repairs; look for leaks, make sure all heads are providing adequate coverage to their area and are closing properly. If the system is not running properly, additional troubleshooting should begin and repairs made. If major issues are discovered, an irrigation specialist may be needed to fix the problems. Replacing backup batteries could also be done at this time.


    Irrigation technology has come a long way over the past several years so if your system is old and not as efficient, now would be a good time to consider upgrading the system. Smart controllers, such as climate-based controllers and soil moisture sensor controllers, provide easier access and more precise control of the system. Add-ons that also make systems more efficient are soil moisture sensors, rain and freeze sensors, and wind sensors. Smart sprinkler heads that provide better coverage without waste are also available.


    Making sure the system is running properly and efficiently now will ensure your landscape plants will be healthy going into the growing season.

  • Planting Bare-Root Plants - David Hillock, Consumer Horticulturist

    Bare-root plants are plants not growing in a container and are packaged and sold with a moist material surrounding their roots to protect them until planting. Because there is less shipping material and weight, bare-root plants can be much cheaper than plants growing in containers or soil. Because bare-root plants are sold while dormant, there is less chance they will be damaged or stressed during shipping too.


    Several species of trees, shrubs, and perennials are offered as bare-root plants. Bare-root plants can be purchased in winter and should be planted in February or March. Bare-root or packaged plants should be dormant (not showing new growth). The bare-root plant is often prepack-aged in a colorful bag. Open the bag immediately and dampen the roots until planting. At planting remove all bags, strings, or wires


    Never leave roots exposed to air. Very fine root hairs, which are not visible to the naked eye, are responsible for moisture and nutrient uptake and are killed when exposed to dry air for even a very short period. Keep the roots damp and covered while preparing the planting hole to protect the fine root hairs.


    Plants should be planted at the same depth at which they were growing in the container or field nursery. There is a texture and color change between the trunk or stem and the roots. The base of the plant should not be covered with more than about one inch of soil. Planting too deep is a major cause of plant failure, especially in poorly drained clay soil.


    Holes for bare-root plants should be dug large enough to accommodate the roots without crowding or twisting. The hole should be no deeper than the original root depth and at least twice the spread of roots. Broken and badly damaged roots should be removed. A mound or cone may be made in the center of the hole to accommodate the spread of roots and allow the tree or shrub to rest at the proper depth while backfilling the hole.


    Work the soil under and around the roots to remove air pockets. Firm the soil while filling until the hole is three-quarters full, and then fill the hole with water. This will settle soil around the roots. After the water has soaked in, finish filling the hole with soil and water again. If the soil around the plant settles, bring it back up to grade with additional soil.

  • Terminating Cover Crops - Casey Hentges, Oklahoma Gardening Host and Bailey Lockhart, Project Coordinator

    Cover crops add a lot of value to the garden, regardless of size. Planting cover crops in winter is like putting armor on the garden when it might not be used. The plants prevent soil erosion from wind and water and also take up nutrients, such as nitrogen that may otherwise leach.


    A few examples of cool season crops are Elbon Rye, Hard Red Winter Wheat, Crimson Clover, Austrian Winter Pea, and Tillage Radishes. The rye and wheat crops will produce mostly vegetative growth which will add organic matter into the soil and improve the health of your garden bed. Legumes, such as clover and Austrian winter peas, will fix atmospheric nitrogen into a plant available form. Tillage radish is a great plant to use because it creates channels through the soil with its taproot. This allows for better water and nutrient infiltration into the soil profile. Because each cover crop has something different to offer, it is best to use a mix of cover crops. Using a mix provides a combination of benefits from the taproot, legumes, and additional vegetation.


    Heading into the planting season means terminating cover crops. This should take place before the plants produce seed, but ideally a few weeks before planting the spring garden. There are a few ways to terminate a cover crop. The biggest question is whether or not you want to till the soil. Using a rototiller is the quickest way to incorporate the plant material into the soil and allows for a nice planting bed for transplants or seeds. However, tilling has been shown to disturb microorganisms that are a vital component in the soil profile. There are a few options to choose from if you prefer to not till the soil. In a large garden plot, a flail mower will knock down vegetation, but a weed eater will suffice in a small garden plot. Another option of not tilling is to use a crimper. These are most commonly seen as a large implement on the back of a tractor that rolls over and breaks the plant stems to prevent future growth. However, in a garden setting, there are smaller versions that can be used to step on the plant to break the stems and lay the plant on the ground. The plants may have some regrowth from the base of the plant whether they are crimped or cut, depending on the weather. If this happens, it is normally minor.


    Both crimping and cutting, leaves plant material to decompose on the soil surface. The material serves as a mulch layer that can prevent weed growth and water evaporation from the soil. On top of these benefits, the mulch will eventually decompose and will improve the garden soil. After terminating the cover crops, all that is left to do is patiently wait for spring to plant warm season crops.


    Find more information about cover crops on the Oklahoma Gardening YouTube channel.


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