Horticulture Update
MARCH 2001

To read or print out individual articles, click on the article in the table of contents.
To read the entire newsletter, scroll down.

Table of Contents
Louisiana Iris: Plant of the Month,
by Dr. William C. Welch
Wildflower Wheel Identifies Texas Wildflowers,
by Diane Bowen
Assessing Ice Damage to Trees,
from the Lamar County Master Gardener newsletter
Sweet Corn Flavor,
by J. B. Jones
Pruning Hedges,
by Dr. Douglas F. Welsh
National Pesticide Telecommunication Network (NPTN)
Collecting Pecan Graftwood,
by Dr. George Ray McEachern
2001 Pecan Management Calendar for Texas,
by Dr. George Ray McEachern
Garden Checklist for March, 2001,
by Dr. William C. Welch
HORTICULTURE UPDATE is designed as a source of information for County Extension Agents and Specialists to utilize in local news releases and as part of their educational programs across Texas, but will also appeal to gardeners and plant-lovers of all kinds, especially those interested in growing plants under the tough conditions of Texas and the Southern United States. Our information is oriented for Texas gardeners and Texas conditions.

Each issue includes a monthly checklist for suggested garden activities along with articles on gardening topics and profiles of plants especially suitable for Texas and the South. Another feature of the publication is information about forthcoming educational opportunities sponsored by the Texas Agricultural Extension Service.

Dr. William C. Welch and Dr. Douglas F. Welsh, both Extension Horticulturists in the Department of Horticultural Sciences at Texas A&M University, share editorial responsibilities for the newsletter. Articles from County Extension Agents (Horticulture), and Specialists in related disciplines are welcome and encouraged.


Editor for March 2001:
Douglas F. Welsh, Ph.D.
Professor and Extension Horticulturist
Texas A&M University, College Station, Texas

Assistant to the Editor:
Cynthia Mueller
Master Gardener, Galveston County, Texas


Louisiana Irises

By Dr. William C. Welch, Landscape Horticulturist
Texas A&M University, College Station, Texas

ouisiana irises are perennials that can be grown successfully in every area of Texas and the Gulf Coast, but thrive best in the eastern third of the state where their ancestors are native. They also occur naturally in Arkansas, Louisiana, and Mississippi.

Mature plant size varies from 1 to 6 feet and flower sizes from 3 to 7 inches across. Flowers occur in March and April. Because all the primary colors are inherent in the various species that contributed to this group, there is no limit to the color range. The Louisianas, for example, include the purest form of red of any iris.

Louisiana irises prefer an acid soil in the range of 6.5 or lower. They like large quantities of fertilizer and water, but their greatest need for both of these comes during the naturally cool and moist fall and winter seasons. They are among the few irises that will thrive in poorly drained soils, and may be effectively used along streams and lakes where they may be inundated periodically during changing water levels. Foliage is lush and requires heavy fertilization to remain healthy and productive.

Some varieties go dormant during the heat of summer, leaving dead foliage that should be cut back or removed. New foliage will appear again in the fall. Fall is the best season for transplanting. Beds should be well tilled and amended with large amounts of compost, peat, or pine bark. Rhizomes should be planted just below ground level and kept moist until well established. Clumps spread quickly, and individual rhizomes should be spaced several feet apart to avoid need for annual division.

Mulching in the summer protects rhizomes against sunscald. Winter protection is not necessary, but could help prevent the evaporation of essential moisture in northern and dry areas of the region. Azalea-camellia fertilizers are recommended, along with water soluble fertilizers designed to lower the soil pH. After bloom is completed in the spring, the stalks should be cut back to the rhizome. Old rhizomes do not bloom again, but increase to produce the following year’s crop.

These flamboyant flowers are attractive to bees, and the visits of these insects often result in pollination and the production of fertile seed in the irises' large seed pods. Ripening seeds sap the plant’s strength, so they should be removed unless, of course, the grower has decided to raise new plants from seed. If so, leave the pods in place until they turn yellow-green in July or August, shell out the seeds before they dry, and plant at once into pots of well-prepared soil. Provide adequate protection over the winter, and plant the young seedlings into permanent locations in March.

Although not always available in a great variety of colors, Louisiana irises are sold by some garden centers in Texas. Mail order sources are another possibility. Special plant sales, such as the Bulb Mart in Houston each fall and March Mart at the Mercer Arboretum, usually offer a wide variety of Louisiana irises.

To read or print out individual articles, click on the article in the table of contents

Wildflower Wheel Identifies Texas Wildflowers

By Diane Bowen, Ag Publications, Texas A&M University

ith the wildflower season approaching, nature lovers can learn more about Texas’ abundant roadside beauties with a new identification wheel, “Texas Wildflowers.”

The wheel was created to help people identify the wildflowers they see along the highways each year. Produced by the Texas Agricultural Extension Service, the wheel features photographs of 16 of the state’s most common wildflowers: black-eyed Susan, bluebonnet, coreopsis, Drummond phlox, gayfeather, Indian blaket, Indian paintbrush, lemon mint, Maximillan sunflowers, mealy cup sage, Mexican hat, pink evening primrose, verbena, bluebell, standing cypress and wine cup.

To help gardeners trying to grow wildflowers, the wheel features both the blossom and the seedling for each species.

“Texas has a worldwide reputation for its wildflowers,” said Doug Welsh, Extension horticulturist.”The wildflower wheel will help Texans, new and old, identify and grow these Lone Star natives.” The wheels detail information about wildflowers, such as the fact that Texas has no law that specifically makes it illegal to pick wildflowers. But it is illegal to trespass on private property or to damage government property (including road rights-of-way). Motorists should not dig up clumps of flowers or drive over them so that others can enjoy them also.

To beautify roadsides, the Texas Department of Transportation sows more than 60,000 pounds of wildflower seeds along highways each fall.

In the past, wildflowers have been used for medicinal purposes: Native Americans made tea from plains coreopsis to strengthen their blood. Gayfeather is also called snakeroot because part of it was once used to treat snakebites. Pioneers brewed a cough medicine from lemon mint. A number of Texas wildflowers are endangered species. One of them, the Navasota ladies’-tresses, grows only in Grimes County.

The wheel also provides tips for growing wildflowers, including:

The new wheel can be viewed on the Web at:

Wildflower Wheel

(click on 'Search' and type in 'Wildflower Wheel', click on 'Find', then select the first item listed: "Texas Wildflower Wheel".)

A wheel costs $10.95 and can be ordered at:

Ordering information

For credit card orders, by call toll-free (888) 900-2577.

To read or print out individual articles, click on the article in the table of contents

Assessing Ice Damage to Trees

From the Lamar County Master Gardener Newsletter

he winter storm left trees looking like there’s no tomorrow. Major limbs have been broken or damaged, foliage has been shredded or stripped, or the bark has been torn or gouged. But what at first glance may look like mortal wounds are not necessarily fatal to a tree. Trees have an amazing ability to recover from storm damage.

The first step is to assess the damage. Before writing off a damaged tree as a “goner,” evaluate trees by asking the following questions:

  1. Other than the storm damage, is the tree basically healthy and vigorous? If the tree is basically healthy, is not creating a hazard, and did not suffer major structural damage, it will generally recover if first aid measures are applied immediately after the storm.

  2. Are major limbs broken? The larger a broken limb is, the harder it will be for the tree to recover from the damage. If a majority of the main branches are gone, the tree may have little chance of surviving.

  3. Has the leader (the main upward-trending branch on most trees) been lost? In species where a leader is important to upward growth or desirable to appearance, it may have to be a judgement call. The tree may live without its leader, but at best wold be a stunted or deformed version of the original.

  4. Is at least 50 percent of the tree’s crown (branches and leaves) still intact? This is a good rule of thumb on tree survivability. A tree with less than half of its branches remaining may not be able to produce enough foliage to nourish the tree through another season.

  5. How big are the wounds where branches have been broken or bark has been damaged? The larger the wound is in relation to the size of the limb, the less likely it is to heal, leaving the tree vulnerable to disease and pests. A two- to three-inch wound on a 12-inch diameter limb will seal over with new bark within a couple of years.

  6. Are there remaining branches that can form a new branch structure? The remaining limbs will grow more vigorously as the tree tries to replace its missing foliage. Look to see if branches are in place that can eventually fill out the tree’s appearance.

  7. Is the tree of a desirable species for its location? If the tree is in the wrong location (such as a potentially tall tree beneath a power line), or an undesirable species for the property (messy fruit, etc.), it may be best to remove it if it has serious damage.

The questions listed above are intended to help you make informed decisions about your trees. In general, the answer as to what to do about a particular tree will fall into one of the following three categories:

  1. It’s a “keeper.” If damage is relatively slight, prune any broken branches, repair torn bark or rough edges around wounds, and let the tree begin the process of wound repair.

  2. Wait and See. If a valuable tree appears to be a borderline case, resist the temptation to simply cut the tree down and be done with it. In such cases, it may be best to stand back for a while and think it over. Remember that time is on your side. After careful pruning of broken branches, give the tree some time to recover. A final decision can be made later. The majority of trees may be classified into this category.

  3. Say Goodbye. Some trees simply cannot be saved or are not worth saving. If the tree already has been weakened by disease, if the trunk is split, or more than 50 percent of the crown is gone, the tree has lost its survival edge. Remember, photosynthesis is the process by which plants grow. Photosynthesis requires sufficient leaves (or needles) to capture sunlight and feed the tree. Significant loss of limbs and leaf sites will drastically reduce the tree’s photosynthesis capacity an ultimately, its ability to recover and survive.

Some trees may have damage that’s too close to call, or may have hidden damage. To help with such questions, a tree professional may be needed to help you decide what to do about your trees. Don’t hire just anyone who slows up at your door following a storm. Ask around for references and experiences by friends and neighbors.

More information can be found by visiting the Texas Chapter of the International Society of Arboriculture website at:

International Society of Arboriculture

Or, go to the Texas Chapter of the ISA at:

Texas Chapter ISA

The National Arbor Day Foundation has helpful hints on their website at:

National Arbor Day Foundation

Also, agencies such as the Texas Agricultural Extension Service and the Texas Forest Service can provide useful information. For more information about the Texas Forest Service, visit:

Texas Forest Service

Information originally provided by the Texas Forest Service, as printed in the Lamar County Master Gardener newsletter ‘Successful Gardening’.

To read or print out individual articles, click on the article in the table of contents

Sweet Corn Flavor

By J. B. Jones, Master Gardener, Lamar County, Texas

he flavor of sweet corn is influenced by a gene that controls its sugar content. The seed corn you buy may have some special genes which are designated su, se, sh, shz, or SB. The very best flavor, or the flavor you want, is available if you pay attention to which of these genes your seed corn has.

The “su” gene is in the standard sweet corn you have grown through the years. It gives a rich corn flavor and the quality is best if it is isolated from field corn, picked and eaten in the same day. Silver Queen, a variety recommended for our area has this gene.

The “se” gene increases the original levels of sugars in the kernels, extends the flavor and slows the loss of moisture from the kernel. These varieties should also be isolated from field corn and have a slightly better flavor if isolated from varieties with the “su” gene. Kandy Korn, a very popular variety in our area, has the “se” gene.

The “sh” gene raises the levels of sugar further, again extending flavor and shelf life. The varieties with the “sh” gene are often called the “super sweets” or “extra sweets.”

The latest development in sweet corn varieties gave us the “SB” gene and these varieties are often called the “sweet breed.” They have an important characteristic. They can be planted near “su” or “se” types without losing flavor. However, they should still be isolated from field corn and varieties with the “sh” gene. High sugar content, long shelf life, good germination in cold soils and vigor characterize these varieties. Varieties with the “SB” gene are not readily available but the very, very similar gene “shz” is present in the All-American Selection, How Sweet It Is.

Check these sweet corn designations when you buy your seed and you may be better satisfied with the flavor.

To read or print out individual articles, click on the article in the table of contents

Pruning Hedges

By Dr. Douglas Welsh, Professor and Extension Horticulturist
Texas A&M University

edges are a row of plants that merge into a solid linear mass. They have served gardeners for centuries as screens, fences, walls and edgings.

A well-shaped hedge is no accident. It must be trained from the beginning. The establishment of a deciduous hedge begins with the selection of nursery stock. Choose young trees or shrubs 1 to 2 feet high, preferably multiple-stemmed. Cut the plants back to 6 or 8 inches when planting; this induces low branching. Late in the first season or before bud-break in the next season, prune off half of the new growth. In 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 the plants to grow untrimmed to the final height before shaping; 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 in order 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 o slightly pointed top and with sides slanting to a wide bas (fig. 1).


After plants have been initially pruned to induce low branching, the low branching is maintained by trimming the top narrower than the bottom so that sunlight can reach all of the plant leaves (Fig. 2).

These questions often arise and the answers depend to some extent on how formal an appearance is desired. How often should this hedge be trimmed? When should I trim? In general, trim before the growth exceeds 1 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 misshapen hedge? If it is deciduous, the answer is fairly simple. In spring before leaves appear, prune to 1 foot below the desired height. Then carefully trim for the next few years to give it the desired shape and fullness. Hedge plants may occasionally decline too much to recover from this treatment, thus making it necessary to replace them.

Rejuvenating evergreen hedges is more difficult. As a rule, evergreens cannot stand the severe pruning described. Arborvitae and yew are exceptions. Other evergreen hedges may have to be replaced.

Tools. What tools should be used to trim hedges? The traditional pair of scissor-action hedge shears is still the best all-around tool. It will cut much better an closer than electric trimmers which 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 are 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.

This material originally appeared in the 'Master Gardener Handbook'.

To read or print out individual articles, click on the article in the table of contents

National Pesticide Telecommunication Network (NPTN)

he National Pesticide Telecommunications Network (NPTN) is a toll-free information service sponsored cooperatively by Oregon State University and the U.S. Environmental Protection Agency. NPTN provides objective, science-based information on a wide variety of pesticide-related subjects, including pesticide products, pesticide poisonings, toxicology, and environmental chemistry. It is staffed by qualified and trained pesticide specialists who have the toxicology and environmental chemistry training needed to help callers interpret and understand scientific information about pesticides.

NPTN receives more than 20,000 calls per year. Most callers are homeowners concerned about their family's health when pesticides are being used in and around their home for the control of ants, cockroaches, termites, fleas, or garden and lawn pests. NPTN can provide information on specific recommendations about which pesticides to use for control of pests, or can direct callers to local resources for products available in their area.

If people call with pesticide emergencies, the NPTN staff can connect them directly to the Oregon Poison Control Center or the National Animal Poison Control Center. Additionally, the staff can refer calls requiring a medical background to a medically trained clinical toxicologist. They can also direct callers to appropriate agencies for assistance with pesticide incident investigations, safety guidelines, clean-up and disposal, and laboratory analyses.

NPTN utilizes a variety of information sources including EPA documents, USDA Cooperative Extension publications, current scientific literature, and pesticide product databases. Non-copyrighted materials can be mailed or faxed to callers for the cost of postage and handling.

Information is also available through the NPTN World Wide Web site at:

http://nptn.orst.edu

NPTN can be reached 6:30 a.m. to 4:30 p.m. Pacific Time seven days a week, excluding holidays. Telephone: 1-800-858-7378. Fax: 1-541-737-0761. E-mail: nptn@ace.orst.edu

To read or print out individual articles, click on the article in the table of contents

Collecting Pecan Graftwood

By Dr. George Ray McEachern, Extension Horticulturist
Texas A&M University, College Station, TX 77843-2134

he Texas inlay bark graft method has become the standard top working technique for pecans throughout the irrigated southwest. Heat, drought, high light intensity, wind and other factors common to the southwest make grafting very difficult. Classic grafting systems used in Europe, California, New York and Georgia for other fruit crops fail in Texas because of these limitations. Along the Gulf Coast many of these other grafts are effective; however, once one moves 200 miles from the humid conditions grafting becomes very difficult.

The four-flap graft has also become popular in Texas because of its easy technique and very high percent of success, even by beginners. Commercial nurseries use the patch-bud graft in the spring, but more commonly in the late summer.

Spring patch-buds will require budwood collected late in the winter just before bud break. Most graftwood is collected in February and early March while the wood is very dormant.

When to Collect Graftwood and Budwood?
The longer one waits to collect wood, the shorter the period of time before bud break after grafting. Ideally, one would like to have three to five weeks after grafting and before the buds begin to grow. This long period will give the cambium tissue of the graft and cambium tissue of the rootstock sufficient time for each to generate new bark and wood which are connected. Once the tissues are connected, water can move from the rootstock wood up into the new graft and success follows. On the other hand, if conditions are not ideal or if there is not sufficient time for the graft/rootstock cambium tissues to generate a connection, the graft or bud will die. Therefore, the time at which you collect graftwood or budwood is very important.

Collect pecan graftwood from February l to March 15. This is the wood which will be used for the Texas inlay bark graft method or the four-flap graft.

Collect pecan budwood from March 15 until primary bud swell. This is the wood which will be used for patch budding. Graftwood will not allow the patch to slip or pop off the graft stick because it is too tight or too dormant. Patch budding in the summer, starting in mid July through August is done with fresh budwood collected the same day you graft. These patches are on current season wood and will pop off and separate from the wood very easily.

Where Do You Collect Graftwood and Budwood?
Strong, rapidly growing one year old wood is ideal for grafting or budding. This is easy to find on young, fast growing trees or in the tops of trees which have just begun to bear. Old trees or slow growing trees should be avoided. If a large number of grafts will be needed, older trees can be dehorned to stimulate compensatory growth. These straight, round, one year old shoots are perfect for grafting or budding.

Drought, freeze or herbicide damaged trees should not be used for graftwood. Trees which are not positively identified also should not be used. All too often, growers will think a tree is a certain variety when it is not. Variety identification is a very important part of graftwood collection. Waterproof ink and metal tags should always be used.

Two year old wood can be used, but it is not as good as current season growth.

How to Process Graftwood and Budwood?
Once the wood is cut from the tree, it should be moved out of the sun to a cool, moist location to wait for processing. The graftwood should be processed for storage the same day it is collected. Cut the graft sticks into 6", 12", or 18" lengths which will give one, two or three grafts per stick.

Process only one variety at a time to prevent mixing the varieties.

Dip the freshly cut ends in orange shellac, grafting wax, paraffin or pruning compound. Orange shellac is ideal because it never dries and new growth from the graft will move over it without delay.

Make sure the primary buds are not damaged or knocked off while processing the wood. This primary bud, or insurance bud as it is sometimes called, has the best chance for growth after the two cambium tissues connect, so caution needs to be practiced to prevent losing it.

A very small amount of moisture should be maintained near the graftwood while it is stored. In the old days this was in wooden boxes with moist wood shavings. Today, paper towels and polyethylene bags are used. Avoid colored plastic bags because they may not breathe. The respiration rate of the dormant grafts in refrigeration is very slow; therefore, the bags should allow carbon dioxide to exit, and oxygen to enter the bag. The paper towels used for maintaining moisture should be squeezed to near dryness. This is accomplished by soaking the towels in water, squeezing the water out with a very strong grip of the hand, and finally stepping on the towels with your foot. Then, take the towel up, shake it out and it is ready to wrap five graft sticks. This will prevent the collection of too much water and the formation of mold on the graftwood. Dr. Loy Shreve always said, "It is better to have no moisture source than wet graftwood." This is very true. So, when you squeeze the wet paper towels, they need to be squeezed dry.

How To Store Graftwood and Budwood?
Once sealed in polyethylene bags with variety and year identification using waterproof ink, the graftwood needs to be stored at 35 to 45 degrees F. until used. Make sure the graftwood does not freeze. The refrigerator needs to be monitored frequently to prevent freezing. A high/low thermometer is good insurance against freezing.

Graftwood can be used only on the year it is collected. Make sure the label is marked for the year and the variety.

Take the graftwood out of refrigeration only as needed. A cool, then warm, then cool cycling of the temperature is not good. Also, move the graftwood to the orchard grafting site in a cooler with ice to keep it from getting hot.

If the graftwood or budwood is collected from strong, fast growing trees and if it is processed and stored properly, grafters should obtain at least 90% survival with the Texas inlay bark graft method or the four-flap graft. Grafting should not be attempted before the sap is moving; there are small leaves on the tree and the bark is slipping. This is usually in early April and grafting can continue until mid to late May, depending on how fast the season becomes hot.

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2001 Pecan Management Calendar For Texas

By Dr. George Ray McEachern, Extension Horticulturist
Texas A&M University, College Station, TX 77843-2134

ecan growers can be optimistic about the 2001 season and there is good reason: we have had a very cool but not extremely cold winter and we have had good rains over most of the state. The 2000 season was very short, so we are expecting a good crop this year. This calendar can be a guide in planning management steps for the up coming season.

January/February

March April May June July August September October November December

To read or print out individual articles, click on the article in the table of contents

Garden Checklist For March, 2001

By Dr. William C. Welch, Landscape Horticulturist
Texas A&M University, College Station, Texas