August Gardening Topics
- Controlling Winter Annual Weeds in Turf - David Hillock, Consumer Horticulturist
Annual bluegrass, rescuegrass, cheat, and downy brome are winter annual grassy weeds. Chickweed and henbit are winter annual broadleaf weeds. For winter annual weed control with herbicides, apply a preemergent herbicide two weeks prior to germination (winter weeds begin germination in late August to early September, if moisture is available; annual bluegrass and chickweed are effectively controlled with preemergence herbicides) or soon after their emergence (October and November) when weeds are young and actively growing. Portrait or Gallery provides good preemergence control of winter annual broadleaf weeds but no control of winter annual grasses weeds. Some preemergence herbicides control both winter annual grasses and broadleaves. All preemergence herbicides must be applied prior to germination and “washed” into the root-zone soil where weed seeds are located. Postemergence control of winter broadleaf weeds in bermudagrass, Kentucky bluegrass, centipedegrass, perennial ryegrass, tall fescue and zoysiagrass is with 2,4-D, dicamba, and MCPP combinations applied in October and November. Note: preemergence herbicides should not be used if planning to overseed or establish cool season grasses this fall. Always read and follow all pesticide label instructions.
- National Pesticide Information Center - David Hillock, Consumer Horticulturist
Have questions about any pesticide-related topic? The National Pesticide Information Center (NPIC) is a national toll-free telephone and internet service that provides objective, science-based information about a wide variety of pesticide-related subjects to the public and to professionals. NPIC answers thousands of questions a year on numerous pesticide topics, including pesticide products and active ingredients, recognition and management of pesticide poisoning, toxicology, and environmental chemistry. NPIC also provides referrals for laboratory analyses, investigation of pesticide incidents, emergency treatment information, safety information, health and environmental effects, and cleanup and disposal procedures. NPIC produces many types of publications including research papers, frequently asked questions, annual reports, outreach materials, podcasts, and other resources available to the public. NPIC can assist people in over 240 different languages using an over-the-phone language service with staff trained in medical and scientific terminology. This same service is used by numerous poison control centers across the United States. This service is sponsored cooperatively by Oregon State University and the U.S. Environmental Protection Agency (EPA).
- How much irrigation water does a peach tree need? - Becky Carroll, Associate Extension
Will my peach trees benefit from irrigation? Yes, for sure!
Water is so important for good quality fruit production. Without adequate moisture, fruit will not size well and may not ripen properly. Late summer drought during flower bud initiation can also produce peaches next season that are “doubles”. We had large numbers of double peaches this season because of dry conditions late summer in 2021. Also, when a large rainfall is received after irregular watering, fruit can split and crack due to the rapid uptake of water. Plus, if you have a period of drought and growth is limited at any time, the growth loss can not be recovered that year. Consistent watering from pit hardening to the final swell will result in the largest fruit.
A mature peach tree with a crop needs about 30 gallons of water per day especially during July and August. Should you water every day? No, watering 2 to 3 times per week to provide the needed moisture will be best. If you receive a rain, count it as about 50% efficient toward the tree’s needs.
How can you get more specific or tailor your irrigation schedule? Tensiometers, moisture meters, or watermark sensors at about 24 inches deep can give a good idea of the moisture at the rootzone where most of the water is taken up. Another irrigation tool is using pan evaporation readings to replace about 60% of the water lost due to temperature, humidity and wind. The pan of water is experiencing similar conditions to your trees If you lose ½ inch in evapotranspiration, you’ll need to water 0.3 inches. Trees without a crop need less replacement, maybe about 40%.
What type of irrigation system works best for applying water? Drip irrigation is normally the system of choice because you lose less to evaporation and the humidity is less under the tree (less disease pressure). On a mature tree, 4 emitters (2 on each side) work well. The entire root system does not have to be irrigated. On sandy soils, drip emitters may not provide enough water to get a good wetting pattern. Micro-sprinklers are a good option to apply more water volume over a larger area. Just make sure they are not spraying the foliage.
If you can’t set up an irrigation system, what can you do?
- Plant trees further apart. Give them about 25 feet between trees to reduce competition with other trees.
- Control weeds around the tree. Weeds compete for water and nutrients.
- Using an annual ryegrass cover crop early season in a peach orchard aids soil water retention and suppressed weeds in test plots. Ryegrass is allowed to grow until it begins competing for water in June, and then killed in place to create a mulch. This was tested at the research station and yield was not increased but fruit size was larger than the standard herbicide strip system.
- If water is limited, concentrate on the last 3 weeks prior to harvest. Fruit ripening requires a great deal of water to develop big juicy peaches.
A ripe peach is about 88% water. Without enough irrigation, the peach will not be a large or juicy. Peaches acquire 2/3 of their volume during the last 30 days ripening. Not much beats a fresh tree ripened peach, providing that irrigation will help get the best quality.
https://extension.okstate.edu/fact-sheets/planting-and-early-care-of-the-peach-orchard.html gives more information on other management needs to grow the best peaches.
- Dividing Perennials - David Hillock, Consumer Horticulturist
As perennials mature, they often need dividing to encourage vigor and continued performance. Luckily the plants provide us a few clues when it is time to divide them - smaller leaves and fewer flowers, weaker stems, the center becomes open, and all the growth is on the perimeter of the clump, or it may have just outgrown its spot.
The general rule for when a perennial should be divided is opposite its flowering time. So, a plant that flowers in the spring can be divided after it flowers, usually in late summer or fall. Late August is a good time to start dividing these types of perennials in Oklahoma. Some plants don’t care when they are divided, but in any case, care should be taken to ensure survival of the new transplants.
Start by digging a trench around the outside of the clump and then lift the entire clump from the ground. Using a sharp knife or spade begin cutting the clump up into smaller clumps about the size of your fist or a gallon sized perennial. Each section should have at least three healthy buds or shoots.
Discard the older unproductive portions and the weak spindly portions and keep the more vigorous sections. Remove any diseased parts and make clean cuts to any damaged roots. Prepare the area by digging wide, shallow holes to accommodate the roots. Place the plant sections in the holes by spreading the roots out over the ground and cover them back up. The crown of the plant should be at the same depth as it was before dividing it. Planting too deep may delay or completely hinder flowering of some species. Water the plants and keep the soil moist for several weeks to encourage new root growth.
If you have extras, share them with a friend.
- Pecan Crop Load Thinning - Becky Carroll
Although pecan crops may be spotty in some areas due to overcropping on some cultivars last year, many pecan growers with improved varieties should be checking crop loads to determine if they need to mechanically thin their pecans. On the largest fruited pecans such as Mohawk and Maramec only about 45-50% of the terminals should have clusters, medium-large sized like Pawnee, 50-60 % and on smaller varieties, like Kanza, 60-70% of terminals can be fruiting. If more terminals are fruiting than recommended, the pecans should be thinned. Native pecans do
not warrant crop management due to less inputs for economical production. Homeowners can use frailing poles to reduce the number of pecans on their trees for more consistent production. Pecans that drop are mostly water at this stage and will dry up and be thrown out the harvester with other trash. In landscapes, dropped nuts can be collected and discarded.
Crop load thinning is usually done the first week or two of August or more specifically when the pecans are in the water stage when the ovule has expanded between 50-100%, (see figure and pictures below). Just as peaches and apples are thinned, pecans will greatly benefit from crop load management. Thinning the fruit load will increase fruit quality, fruit size and kernel percentage. It will also help reduce alternate bearing. Pecans are an alternate bearing crop, producing a large crop one year and reduced or no crop for the next year or two. When the tree is overcropped, it is using all its reserves to ripen the crop plus trying to initiate fruit buds for the following season. Fruit thinning also can reduce the possibility for and severity of winter freeze damage. Many growers have said that they should have reduced their crop last year especially on Pawnee because they have a reduced crop of Pawnee this year. Even though total yield will be reduced following crop thinning, marketable yield may be even greater due to increased quality.
Pecans can be mechanically thinned with a conventional shaker fitted with donut pads. Be sure to keep the underneath of the flaps on the donut pads greased to help limit barking the trees. Fact Sheet HLA-6251 – Pecan Crop Load Management details the procedure.
A video demonstrating how to determine crop load, pecan development, and equipment used is available at https://youtu.be/yHgkFur7nGs. It shows the thinning process from the ground and tree top level with drone footage.
The drawing shows a pecan cut longitudinal exposing the ovule at 50% expanded. These August 5, 2021, photos show the differences in ovule expansion. The top picture is a Pawnee showing the ovule expanded to about 80%, left photo is Kanza at 100% and the right is Maramec at around 40%.
- Pruning Shrubs as Hedges - David Hillock, Consumer Horticulturist
Hedges are a row of plants that merge into a solid linear mass. They have served gardeners for centuries as screens, fences, walls, and edging. A well-shaped hedge is no accident. It must be trained from the beginning.
Establishing a deciduous hedge begins with selection of nursery stock. Choose young trees or shrubs one to two feet high, preferably multiple-stemmed. When planting, cut the plants back to six or eight inches; this induces low branching. Prune off half of the new growth late in the first season or before bud-break in the next season.
The following year, again trim off half. In the third year, start shaping. Trim to the desired shape before the hedge grows to its desired size. Never allow plants to grow untrimmed to the final height before shearing. By that time, it is too late to get maximum branching at the base. Do not allow lower branches to be shaded out. After the hedge has reached the desired dimensions, trim closely to keep the hedge within chosen bounds.
Evergreen nursery stock for hedging need not be as small as deciduous material and should not be cut back when planted. Trim lightly after a year or two. Start shaping as the individual plants merge into a continuous hedge. Do not trim too closely because many needle-bearing evergreens do not easily generate new growth from old wood.
Hedges are often shaped with flat tops and vertical sides; however, this unnatural shape is seldom successful. As far as the plant is concerned, the best shape is a natural form, with a rounded or slightly pointed top and with sides slanting to a wide base (Figure 1).
After plants have been initially pruned to induce low branching, maintain by trimming the top narrower than the bottom so that sunlight can reach the base of the plant (Figure 2).
This question often arises: How often and when should a hedge be trimmed? Answers depend to some extent on how formal an appearance is desired. In general, trim before the growth exceeds one foot. Hedges of slow growing plants, such as boxwood, need to be trimmed sooner. Excessive, untrimmed growth will kill lower leaves and will also pull the hedge out of shape. Trimming frequency depends on the kind of shrub, the season, and desired neatness.
What can be done with a large, overgrown, bare-bottomed, and misshapened hedge? If it is deciduous, the answer is fairly simple. Before leaves appear in the spring, prune to one foot below desired height. Carefully trim for the next few years to give it the desired shape and fullness. Occasionally, hedge plants may have declined too much to recover from this treatment, making it necessary to replace them.
Rejuvenating evergreen hedges is more difficult. As a rule, evergreens cannot stand the severe pruning described above and may have to be replaced.
The traditional pair of scissor-action hedge shears is still the best all-round tool for trimming hedges. It cuts much better and closer than electric trimmers that often break and tear twigs. Hand shears can be used on any type of hedge, while electric trimmers do poorly on large-leaved and wiry-twigged varieties, and sometimes jam on thick twigs. Hand shears are also quieter, safer, and less likely to gouge the hedge or harm the operator.
Hand pruners are useful in removing a few stray branches and are essential if an informal look is desired. Large, individual branches can be removed with loppers or a pruning saw. Chain saws are not recommended for use on hedges.
- Successful Fall Gardening Starts with Good Plant Establishment - David Hillock, Consumer
Gardening is a year-round activity. Those who garden develop an appreciation and a desire for fresh, nutritious vegetables and fruits. In many situations, the best way to obtain fresh vegetables is to grow them at home.
Some of the best quality garden vegetables in Oklahoma are produced and harvested during the fall season when warm, sunny days are followed by cool, humid nights. Under these climatic conditions, plant soil metabolism is low; therefore, more of the food manufactured by the plant becomes a high-quality vegetable product.
Successful establishment of a fall garden starts with the planting of seeds and obtaining transplants made available in the garden centers.
Climatic conditions of July and August involve high soil temperature, high light intensity, and rapid drying of the soil, resulting in an increase in problems of obtaining a uniform stand of plants. Achieving a full stand of plants in the heat of summer may require special treatments. This might include shade over rows when seeded and supplemental watering to reduce soil temperature and aid in seed germination.
Viable seed, to germinate or sprout, must have the proper temperature, adequate moisture, and sufficient oxygen. The surface of the soil, when exposed to the summer sun, may become very hot (140°F). Vegetable seeds should be planted no deeper than three times the diameter of the seed. With small seed such as carrot, this would be no more than 1/4 inch deep. At this depth and exposed in the hot soil, death of the seed due to high temperature would probably occur. It is also likely that such a soil, even when watered, might dry out quickly because of the high temperature. Unless the soil remains moist at the depth where the seeds have been planted, germination will not take place.
To achieve proper temperature and adequate moisture, apply mulch over the row following planting and watering or use materials such as screen wire strips, shade cloth, or boards to cover the row. This will moderate both soil temperature and soil moisture. Remove covers after seedling emerges.
Another desirable practice is to open the soil for the row somewhat deeper than in spring planting. The seeds are planted in this furrow, covered, and watered. In this manner, only the narrow trench would be watered, thus conserving a limited water supply. Later, one may cultivate along the sides of the row and fill soil to the same level of the remainder of the garden. In so doing, one may cover small grass and broadleaf weed plants that might be growing in the row.
Some vegetables are most easily grown by planting seeds in a small seed flat, setting them in individual containers to grow for approximately one month, and then transplanting them to the garden. Those that respond most favorably to this method of handling include broccoli, cauliflower, Chinese cabbage, leaf lettuce, Brussels sprouts, and cabbage.
Prior to setting them in the garden, transplants may be conditioned or toughened by a reduction in the amount of water supplied and by exposure to full sunlight. This might require three to five days. Plant them in the garden in late afternoon to early evening to reduce transplanting shock. Water the plants as they are set. A water-soluble fertilizer may be used at this time, if necessary—following label directions.
To achieve maximum germination of lettuce seed, the planted and watered seed flat should be kept cool. This can be accomplished by placing the seed flat in a cool (60° to 70°F) location for four or five days, at which time seed may begin germinating. The seedlings should be transplanted to individual containers within a few days.
When purchasing transplants in the fall from the garden center be sure to inspect them carefully for unwanted pests. Transplants coming from the greenhouse may also need to be conditioned before setting them directly into the garden. For additional tips on establishing a fall garden see OSU Fact Sheet HLA-6009 Fall Gardening.
Fall Planting Guide
- Protect your Home from Wildfire with Firewise Plantings - David Hillock, Consumer
Wildfires have been raging in the western state but luckily, we have been blessed with good rainfall to keep things relatively green; however, weather can always change and become hot and dry, and we are no strangers to wildfires. Even winters can be very dry increasing the potential for wildfires. Lives, homes, livestock, pastureland, crops, and thousands of miles of fencing can be lost to the flames.
Although a wildfire does not discriminate among its victims, there are some steps homeowners can take to help protect their property from fire, whether it be a wildfire or an accidental fire at home caused by a charcoal grill during a cookout.
The key to keeping a fire at bay is to not provide fuel for the fire. There are plants and shrubs available that are more fire-resistant than others. Fire-resistant plants are those that don’t readily ignite from a flame or other ignition sources. Although the plants themselves can be damaged or killed by a fire, their foliage and stems don’t significantly contribute to the fuel and, therefore, the fire’s intensity.
Seeing a need for information for homeowners, several agencies, including Oklahoma State University Cooperative Extension, joined forces in the early 1990s and coined the term Firewise. This became a catalyst for educational resources and programs to help homeowners, communities, and firefighters to make sensible choices in the wild land/urban interface, which would in turn help control wildfires and protect property.
When selecting plants to include in a Firewise landscape, homeowners need to identify plants with a low flammability rating for areas nearing the home. By selecting plants with certain characteristics, you can reduce the flammability potential of your landscape and provide habitat for wildlife. There are several factors that influence the fire characteristics of plants, including plant moisture content, age, total volume, dead material, and chemical content.
Plants with low flammability don’t accumulate large amounts of combustible dead branches, needles or leaves as they grow. They also have little dead wood and tend not to accumulate dry, dead material within the plant. They have open, loose branches with a low volume of total branches. Many of our deciduous trees and shrubs are fire resistant.
Leaf characteristics is something else to consider. Leaves that are moist and supple, such as the sedum leaf, are more resistant to fire.
Many herbaceous perennials make excellent Firewise plantings. Some remain green in the winter, which in turn reduces their flammability.
Oils and resins found in the sap of some trees and plants such as pine, juniper, cedar, and Yaupon holly, makes them extremely flammable. Homeowners who want to use these plants and trees in the landscape should avoid placing them adjacent to their homes and other structures on the property.
In addition, plants that accumulate dry or dead material such as twigs, needles and leaves should not be planted against the house. This includes many vines like trumpet creeper and ornamental grasses. In winter, these plants have large amounts of dry material and are extremely flammable, allowing a wildfire to spread rapidly.
As you plan out a new landscape or add to an existing one, be sure to consider fire potential in your plant selections. For more information on Firewise, please visit www.firewise.org.