Plant of the Month
By Dr. William C. Welch, Landscape Horticulturist
Louisiana 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 yearâs 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 plantâs 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.
Lawn and Garden News
YARROW
By Dr. William C. Welch, Landscape Horticulturist
A sometimes-used common name for the yarrows is "sunfern." This aptly describes their foliage and preferences for at least partial sun. Achillea millefolium is native to Europe, but naturalized in the Southeast so that it is often considered a wildflower in Texas. In spite of their delicate appearance, yarrows are relatively drought tolerant and withstand heat well. They prefer a good soil with little competition from trees and other competitive plants, but can exist in less hospitable surroundings. Yarrows may be propagated from seed or division. They are prolific spreaders, but can easily be kept in bounds by occasional division or the removal of unwanted plants. Fall division is ideal, but other times, except the hottest summer months, work almost as well. The yarrow's attractive, fernlike foliage is evergreen throughout most of Texas and the Gulf South. They bear their large, flat heads of flowers over a long season, and the blossoms are excellent for drying. To maintain some of the original color, cut and dry the flower heads before pollen forms. If cut later, the flowers are still useful for dried arrangements, but will usually turn brown.
The white-flowering yarrow found growing most often in our area is A. millefolium. It has all the virtues of the species, but most selections have flowers of a less-than-pure white that can have a somewhat dirty appearance. A. millefolium 'Fire King' is probably the most popular and available of the pink-flowered selections of the naturalized species. Flower color is dark bright-pink in spring but fades to paler tints as the heat intensifies. Growth and flowering slow down or nearly stop during the heat of summer, to be followed by occasional re-bloom and growth during the fall. A. millefolium is well adapted to nearly all areas of Texas and the Gulf Coast. It is the yarrow species of choice for the areas near the Gulf Coast, since it seems to withstand the high humidity and hot night temperatures better than the other forms. A. filipendulina 'Coronation Gold' is the most popular garden form of yarrow, but is not as well adapted to areas close to the Gulf. For more inland locations, it is fine. Its gray-green foliage is coarser in texture than that of A. millefolium, and not so finely cut. "Coronation Gold' is a useful plant for locations in Zone 8 and north. Other A filipendulina cultivars worthy of note are 'Moonshine', which is a beautiful combination of pale- and bright-yellow flowers, and 'Gold Plate', which is similar to 'Coronation Gold', but taller and with larger flower heads. The extra height and flower size of 'Gold Plate' make staking a necessity.
GYPSUM: TO APPLY OR NOT TO APPLY?
By Gene R. Taylor II Ph.D. Turfgrass Extension Specialist, and Tony L. Provin Ph.D. Director of TAEX Soil, Water and Forage Testing Lab
Home owners are typically inundated with many sources of information on how to improve soils in the landscape. The claims of some products are almost miraculous in their ability to improve the quality and workability of soils. Other products are firmly entrenched in the minds of gardeners and landscape professionals alike for their supposed ability to improve soils. Gypsum is one of these products. It is generally thought that gypsum will improve the structure of soils. While this claim is not necessarily false in all cases, in Texas many home owners may not see any positive soil improvements from an application of gypsum. To determine if an application of gypsum will help your soil, you first need to know a little about gypsum and how it reacts in the soil. Gypsum is the common name for calcium sulfate, a very water-soluble form of calcium. This makes it a good source of plant-available calcium and sulfur. In most soils, calcium is primarily responsible for helping to hold clay particles together into clumps, clods, or peds, thus ultimately improving soil structure. In most Texas soils, the concentration of calcium in the soil is already high, so an application of gypsum will not significantly improve soil structure. Also, the addition of sulfate sulfur -- a good source of plant-available sulfur -- will not significantly reduce the pH of the soil.
So you ask yourself, when would an application of gypsum be worthwhile? The most practical use of gypsum in Texas soils would be to encourage the displacement of sodium through the soil. Many municipal and private water sources in Texas contain naturally high levels of sodium. Irrigation with waters high in sodium in the landscape often leads to the buildup of sodium in the soil. When sodium concentrations in the soil get too high, clay in the soil may become dispersed. When clays disperse, the individual clay particles are no longer held together, thus releasing the clay particles to move through the soil and concentrate in a single dense layer. Frequently, this layer of dispersed clay is so dense that the movement of water oxygen is severely limited, and roots find it difficult to penetrate the layer. In situations such as this, applications of gypsum can provide a dramatic improvement in returning the soil to its original condition. The next issue would be to determine how much gypsum you should apply to your soil. The only effective method is to have your soil tested to determine the concentration of sodium in the soil. The rate of sodium buildup in the soil will be affected by soil type, species of plants grown, irrigation frequency, and the level of sodium in the irrigation water. The Texas Agricultural Extension Service Soil, Water, and Forage Testing Laboratory offers a variety of soil testing services to the public at a nominal charge. To find out more about soil testing, contact your local county Extension service office. Hint: When you submit a soil sample make sure to ask for appropriate gypsum recommendations. Applications of gypsum typically range from a minimum of 40 pounds per 1,000 square feet to a maximum single application of 175 pounds per 1,000 square feet. Multiple applications of gypsum may be required on soils that are severely impacted by sodium. Gypsum is best applied in the spring and fall when rainfall will enhance the dispersion of the calcium throughout the soil.
WHEN TO PRUNE FLOWERING SHRUBS
By Douglas F. Welsh, Landscape Horticulturist
If a shrub is grown for its flowers, time the pruning to minimize disruption of blooming. Spring-flowering shrubs bloom on last season's growth and should be pruned soon after they bloom. This allows for vigorous summertime growth and results in plenty of flower buds the following year. Some examples of shrubs that bloom on last seasons's growth are:
Cercis canadensis - Redbud
Chaenomeles japonica - Japanese Quince
Chionanthus virginicus - Fringe Tree
Forsythia spp. - all Forsythia species
Lonicera spp. - Honeysuckle
Rapheolepis indica - Indian Hawthorn
Rhododendron spp. - Azaleas & Rhododendrons
Rosa spp. - Rambling Rose species
Spiraea spp. - early white Spirea species
Viburnum spp. - Viburnum species
Some shrubs that bloom after June usually do so from buds which are formed on shoots that grow the same spring. These shrubs should be pruned in late winter to promote vigorous shoot growth in spring. Examples of shrubs that bloom on current season's growth include:
Abelia X. grandiflora - glossy Abelia
Buddleia davidii or B. globose - Butterfly Bush
Hibiscus syriacus - Shrub Althea
Hydrangea arborescens - Hills of Snow
Hypericum spp. - Saint-Johns-wort
Lagerstroemia indica - Crape Myrtle
Rosa spp. - Bush Rose
Vitex agnus-castus - Chaste Tree
For complete information on pruning shrubs, consult our website: www//aggie.horticulture.tamu.edu
PLAN FOR DISEASE PREVENTION IN VEGETABLES
Excerpted from an article in TAEX's ãTexas Earth-Kind Landscape and Gardening Guidelinesä
Home gardeners are constantly pestered with diseases that rob them of their harvest. Many gardeners have found that planning properly and following recommended control practices keep vegetable losses to a minimum.
1. Select a well-drained garden site to prevent damping-off and other problems associated with wet soils.
2. Organic matter (straw, leaves, drop residue) is essential to a productive soil, but it can also increase the occurrence of southern blight. To avoid this, bury organic matter below the expected root zone of next year's crop. This should be done in the fall if possible.
3. Water plants in the morning, rather than the evening, for fewer leaf disease problems. Drip irrigation also reduces foliage diseases.
4. Don't save seed from the garden for planting the following year, since certain vegetable diseases are seed-transmitted.
5. Diseases caused by fungi cannot be cured, so they must be prevented. When you see a fungus problem, irreversible damage already has been done. Cloudy, damp mornings encourage the growth of fungus spores; when such conditions exist, you may want to follow a preventive spray schedule and remove contaminated plants.
6. Grow vegetables in the same location only once every 3 to 5 years. If this cannot be done, plan your garden to avoid growing vegetables of the same family group in the same area season after season.
Family Groups:
1) watermelon, cucumber, squash, cantaloupe, honeydew melon, pumpkin
2) cabbage, cauliflower, Brussels sprouts, rutabaga, kale, turnip, mustard, radish, collard
3) Swiss chard, beets, spinach
4) pepper, tomato, potato, eggplant
5) carrot, parsley, parsnips
6) onions, garlic, leeks, shallots
7) sweet corn
8) beans, peas, and southern peas
FRUITING PLANTS NEED DRAINAGE
This article appeared in ãFruit Gardening in the Landscape,ä published by the Texas Agricultural Extension Service
For productive, long-lived fruiting plants, a well-drained soil is needed. Unfortunately, the average home owner only has a small plot, and must work with what he or she has. In deciding whether or not fruiting plants are adaptable to an area, some general observations are useful:
1. Does water stand for long periods of time?
2. What is the areaâs native vegetation?
3. Are there many yellow (iron deficient) plants around?
If a yard has an area where water stands for long periods after rains, or the soil stays wet for a prolonged time, avoid these areas and soils for fruit, because most fruiting plants do not tolerate wet roots. Standing water or wet soil actually causes root death from lack of oxygen. A quick check for suitable water drainage is to dig a hole 30 inches deep, and fill it with water. If the water is gone within 24 hours, drainage is usually acceptable. Any soil that does not drain within 48 hours is considered unacceptable for most fruiting plants. If the soil so poor that it is not acceptable for the plants you wish to grow, raised beds can be used with limited success. Remember that plants, especially trees, will not live as long, planted in this manner, as they would if planted in a good soil at ground level. Raised beds for fruit trees such as peaches should be at least 8 feet square and 12 inches deep. Do not use highly organic soils to make beds, as the trees may grow later in the year and be more subject to freeze injury. Construct raised beds with a frame of railroad ties or edging timbers, or simply mound the soil, and plant atop the mound.
PLANT PECANS, OTHER NUT VARIETIES IN TEXAS
This article appeared in ãFruit Gardening in the Landscape,ä published by the Texas Agricultural Extension Service
Pecans
The pecan, which is the state tree, is native to some 150 counties. As such, it is popular for its aesthetic value in the landscape as well as for the tasty nuts obtained in the fall. Despite their appeal, pecans are not care-free trees. Even with the limitations of soil requirements, need for regular zinc spraying, and numerous insect and disease pests, pecans are universally adapted to the home landscape. Pecans grow best in deep, well-drained soil. They do not tolerate Îwet feetâ or poor drainage. All pecan varieties require cross pollination; however, in most cases, sufficient pollen is available. In isolated instances, check on pollination before selecting varieties. There are hundreds of named varieties, and literally millions of unnamed varieties, since pecans no not Îcome trueâ from seed. Every native or seedling pecan tree is a separate and distinct variety. Seedling (ungrafted, grown from seed) trees make very good landscape trees. Nut quality on seedling trees is variable, but often good. Those trees do better than improved varieties if grown under minimal landscape management. Improved varieties usually require zinc, nitrogen, and water and pest management to maintain healthy trees. Plant pecan trees at least 40 feet apart in the home landscape, and at least 20 feet from major buildings and property lines. Cut the trees back by half at planting. Train them to a Îcentral leaderâ with a single central trunk and wide-angle branches.
Walnuts
Black walnuts and carpathian (English) walnuts are climatically adapted to essentially all parts of Texas. Several species of black walnuts thrive as natives in Texas. They are of little value as nuts because of their thick hard shells. Improved black walnut varieties, such as Thomas, are commonly propagated and sold through nursery sources. The acid and neutral pH soils of East and North Texas are suitable for carpathian walnuts, but common rootstocks used for carpathians do poorly in the extremely alkaline soils of South, Central, and West Texas. Carpathians thrive in western portions of Texas if they are grafted onto the native Central and West black walnuts -- Juglans microcarpa (Texas Black walnut) or Juglans major (Arizona black walnut). Very few nurseries propagate these native black walnuts as rootstocks, so this is usually a do-it-yourself project. Carpathian walnut trees are smaller than pecans, and can be planted as close as 25 feet apart. Care of walnut trees is much the same as for pecans. Walnut blight is the most serious problem with carpathian walnuts. Disease pressures are greatest in East Texas and coastal areas. Walnut blight can infect young nutlets during the bloom period and as nuts approach maturity. Plant blight-resistant varieties (Reda or Hansen) in more humid areas.
Pistachios
The nut-bearing pistachio is best adapted to the more arid portions of West and Central Texas. Disease pressures make success difficult in East Teas and in coastal areas. Pistillate (female) and staminate (male) flowers are produced on separate trees. Plant at least one male for every 10 female trees. The Kerman (female) and Peters (male) varieties are by far the most common. Pistachio trees are difficult to obtain in Texas because most propagating nurseries are in California, and the trees are generally started in containers, making them more expensive to ship. Nurseries can order trees if they donât already carry them. Pistachio trees are relatively small at maturity, and can be planted as close as 15 to 20 feet apart. They usually begin to bear 4 to 5 years after planting. Nuts mature in the fall.
Chestnuts
The Chinese chestnut is the only chestnut that is reasonably adapted to portions of Texas. This tree is tolerant to the chestnut blight that has killed most native American chestnuts throughout the east and central United States. Chinese chestnuts grow best in the acid soils of East Texas, and are poorly adapted to the extremely alkaline soils of South, Central, and West Texas. Many of the Chinese chestnut trees purchased through nursery sources are seedling trees. Several grafted varieties, including Nanking, are also available. Plant Chinese chestnuts at least 30 feet apart. Care of chestnut trees is much the same as for pecans. In the early years, prune only enough to develop a single trunk and basic scaffolds. Excessive pruning delays the onset of bearing.
Note limitations for these fruits, nuts
Catalogues paint pretty pictures that tempt us to try at least one of everything, but not all fruits and nuts are adapted to all parts of Texas, and sometimes are not adapted at all. Reasons for poor adaptation vary from temperature-related problems to humidity and disease limitations. Some of the more notable fruit and nut crops which have problems in some areas are:
Almonds. Trees are well adapted, but they bloom early and usually lose their crop to late winter freezes.
Apricots. The trees are well adapted to all areas except extreme South Texas; however, fruiting is inconsistent in much of the state. Poor fruit set is often blamed on freeze damage from early bloom and on self-unfruitfulness of varieties, but apricots usually bloom no earlier than peaches, and essentially all varieties are self-fruitful. Fruit set is more consistent in arid West Texas than in central and eastern areas of the state.
Cherry. Most of Texas lacks sufficient winter chilling needed to produce a normal bloom. Sour cherry varieties, such as Montmorency, bear with fair consistency in North Texas. Sweet cherry varieties are winter-killed due to fluctuating temperatures, and are unadapted to all of Texas.
Filbert. The filbert (hazelnut) is poorly adapted to hot Texas summers. It is best adapted in climates that do not exceed 90 degrees F in the summer.
Gooseberry and Currant. These berries will not tolerate our hot Texas summers, and are seldom fruited here.
Kiwifruit. Kiwifruit has proven to be difficult to grow in Texas. The major limitations include susceptibility to freeze injury, only fair heat tolerance, and poor wind tolerance. A separate species of kiwifruit with much greater cold tolerance is being promoted in garden catalogues. It has a smaller, less desirable fruit than commercially available kiwifruit.
Macadamia. Macadamia nut trees are tropical and cannot withstand temperatures below 25 degrees F. Hardiness varies according to species. Test results of macadamias in Texas are not known, but the only area with possible adaptation is the Lower Rio Grande Valley.
CONTROL DISEASES IN FRUIT, NUT CROPS
This article appeared in ãFruit Gardening in the Landscape,ä published by the Texas Agricultural Extension Service, College Station
Home owners involved with growing fruit and nuts often experience reduced fruit quality or quantity due to plant diseases. Fruit and nut crops are susceptible to one or more disease problems throughout their life. Effective disease control involves using both cultural and chemical practices. Most diseases which infect fruit and nuts are caused by bacteria, fungi, viruses, or nematodes.
Bacteria. Several bacteria cause serious problems on fruit plants. Fire blight of pear and apple, bacterial leaf spot, and bacterial canker of peach and plum are three of the more frequently observed diseases in the home garden. Bacterial diseases are found in all areas, but are generally more severe in areas of high to moderate rainfall. Bacterial diseases are controlled by resistant varieties, fungicides, and cultural practices.
Fungi. This group of organisms is the most widespread and damaging to fruit and nut crops. Fungi survive on diseased plant material or on alternate crops. Vascular wilts, root, trunk and fruit rots, and leaf spots are all symptoms of fungal infection. Disease problems are the most severe during periods of high humidity or when the plant tissue is covered by a thin film of moisture. Temperatures between 70 degrees F and 85 degrees F are favorable for most fungi.
Viruses. Viruses are sub-microscopic pathogens that increase in numbers once they are inside the host plant. Viruses can be spread by infected propagating material,
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