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Month-by-Month Gardening Guide: March

Trees and Shrubs:

Now is the time to transplant your still-dormant deciduous shrubs and trees and to plant new trees and shrubs.  It’s also a good time to remove invasive pest plants like English ivy and Japanese honeysuckle that grow around and up tree trunks and may be detrimental to the tree’s health.  It is also a good time to remove other invasive exotic vine species like  Oriental Wisteria and Oriental Bittersweet vines.  The UT Extension Publication W231 provides information on removing English Ivy as well as suggestions on alternative native vines.

A common question is whether you should prune your flowering shrubs in spring or fall.  The rule of thumb is to prune spring flowering shrubs after blooming, so now is not the time to prune spring flowering shrubs like azaleas, rhododendron, flowering quince.  Now is the ideal time, however, to prune your summer flowering trees and shrubs such as hibiscus, hydrangea, crape myrtle and butterfly bush.  A word about crape myrtle — although it is still fashionable, it is not good gardening practice to lop off the top of the plant.

Watch your evergreens (spruce, pine, junipers, hemlock and arborvitae) for spruce spider mite activity in March and April. This cool season cousin to the better-known two-spotted spider mite, over-winters on host plants and will begin hatching soon. Early detection is key to control. Often the yellowing and bronzing of needles are the first signs of a problem to the unwary gardener, but for the more experienced that monitor for pests, the mites are an easy to find. To check for spruce spider mites, place a white sheet of paper under a branch and shake the branch over the paper. If mites are present, they will be the size of walking periods. If 10 or more are present per sample, treatment is recommended. Some non-chemical treatments that can keep spider mites under control in the landscape include a forceful jet of water from a hose. This dislodges the mite while maintaining natural predators. Some beneficial predators can be purchased and released (lady beetles, lacewings, and predatory mites) to feed on spruce spider mites. In heavy infestations, miticides such as Kelthane and Floramite can give a quick knock down but excessive use can lead to resistance. Heavy attacks that go unnoticed may result in branch dieback or death of the plant, so monitoring is important.

A common pest to American and English varieties of boxwood, the boxwood psyllid, becomes active in spring as the buds begin to grow and leaves unfold. The young nymph of the psyllid will suck sap from the new leaves causing them to curl. Nymphs will remain under the curled leaf feeding until they molt to the adult stage in May or June. Host plants are rarely injured beyond the leaf cupping. Treating now with Orthene or Talstar will give favorable control.

Winter can be tough on fall-planted trees and shrubs. Do a thorough inspection this spring for some of the following problems:

  • Bark cracks – These are found most often on maple, apple, beeches, and other thin barked trees. Winter temperature extremes will cause longitudinal bark cracks to occur, most often on the south facing side of solitary trees in full sun. Using tree wrap during winter or planting dense shrubs on the tree’s southern exposure can help prevent this problem. Healthy trees will eventually form callus tissue and heal from the damage. Watch for insects and be sure to water during drought periods the following year.
  • Sun Scald – Similar to bark cracks, sun scald also is found on the south or southwest side of a tree. It is characterized by elongated, sunken, dried areas of dead bark. Sun scald occurs on winter days when the sun heats the bark to the point of cambial cell activity. As the temperatures drop at night, the active cells die and leave behind a sunken area. Wrapping trees in a light-colored tree wrap can help prevent sun scald. This should be applied from two winters (for thick barked trees) up to five winters (for thin barked trees). Do not leave the tree wrap in place during the summers. To repair sun scald damage, use a knife to trace the wound, rounding off any sharp corners to speed healing. Do not use a wound dressing but do consider treating the surface with an insecticide and fungicide to prevent other problems.
  • Dieback – To prevent winter dieback of trees and shrubs, avoid late summer pruning and fertilizing since vigorously growing plants in late fall are most susceptible.
  • Frost Heaving – Freezing and thawing of the soil in fall or spring can cause newly planted trees and shrubs to rise out of their planting hole, damaging roots in the process. Gently resettle plants with your foot or spade making sure to eliminate air pockets. A 3 to 4 inch layer of mulch will help prevent this problem.
  • Animal Damage – Deer and rodents can cause damage to plants, especially during tough winters. These animals feed on the tender twigs, bark, and foliage of trees and shrubs. Deer can also cause damage by rubbing their antlers on trees. To prevent rodent damage, place a cylinder of ¼ inch mesh hardware cloth around the trunk, beginning two inches below the ground up 24 inches on the trunk. Be sure to remove the mesh during the summer. Repellents such as Hinder, Deer-Away, Ropel, and Thiram may provide some control of deer when sprayed or painted on trees. Rags dips in repellents and tied to the tree may also prove effective. In extreme problem cases, fencing may be your only solution to managing deer.

Fruits and Nuts:

One of the first items on your list should be to remove last year’s canes from raspberries and blackberries.  Blueberries should not be pruned at this time of year because the new growth will be producing this summer’s berries.  There is still time to finish fruit tree pruning this month.  Look for broken limbs caused by winter storms.  Dead limbs, root suckers, crossing or rubbing limbs, and downward hanging limbs should also be removed.

Spring is an excellent time to plant fruit bearing plants, including blueberries, strawberries, currants, boysenberries and grapes.  Blueberries are an excellent fruit bearing plant as well as an aesthetically pleasing addition to any landscape.  For our area, Rabbiteye varieties are most adaptable.  One important growing requirement to remember when selecting a variety is their need for cross-pollination in order to set fruit. Because of this requirement, you will need to plant more than one of a recommended variety.  Recommended varieties include: Briteblue, Bluebelle, Climax, Garden Blue, Southland, and Tifblue.  A common blueberry combination is Climax and Tifblue varieties. Blueberries are related to azaleas and as such can tolerate shade, however to produce a lot of fruit you should select a site in full sun. Soil pH is important since blueberries prefer an acidic soil of 4.8 to 5.2, so take a soil test before planting. Like azaleas, blueberries cannot tolerate wet feet and must be planted in a well-drained site. Select a site that is away from ‘frost pockets’ where frost and freeze damage can hurt fruit production. Space plants 5 feet apart in the row and rows 10 to 12 feet apart. Plant blueberries at the same depth they were grown in their containers and remember to water at planting and twice weekly during the first year. Blueberries do not require a lot of fertilizer and there is no need to fertilize at planting.  A slow-release fertilizer can be applied during the following spring and after harvest. After planting, remove about a third of the plant’s height and any branches crossing back into the center of the plant. Removing the fruit buds the first season will help the plant develop strong shoots and roots even though it means your first harvest will be delayed.  Blueberries will benefit from a top dressing of Magnesium sulfate (Epsom salts) as will all your flowering shrubs including roses.  Just sprinkle two or three tablespoons around the base of the plant and lightly work into the soil.  For more information about blueberries, go to UT Publication SP 284-D.

Sprays to reduce many of the Botrytis (gray mold) infections are must this time of year. You should begin sprays of Captan at early bloom and again at full bloom, when close to 90% of the blooms have opened. Keep in mind the bloom period for strawberries can be very long. Also, avoid the use of insecticides during the bloom stage to protect your pollinating bees.

Most home grape plantings will require a preventative application to avoid problems with black rot, which can completely destroy a crop. Begin using Captan, ferbam or mancozeb with malathion when the first shoots are 2 to 4 inches long and continue weekly until bloom. These sprays are critical for black rot control and are helpful in controlling grape phylloxera, flea beetles and plant bugs. When most of the blooms have fallen, treat again using your same combination. If you’ve had a problem with powdery mildew in the past, add Immunox or sulfur to this spray and continuing cover sprays. Cover sprays begin a week to 10 days later and every two weeks till harvest. Multipurpose fruit sprays are available to homeowners that combine a fungicide with an insecticide. These can replace the mixtures listed above, but be sure to read the label.

Groundcovers and Lawns:

Your cool season fescue lawn will benefit from ½ lb. of nitrogen per 1000 sq. ft. on March 15. A second application can be made at the same rate on April 15. Your goal should be to put no more than 1lb of nitrogen down over a 1,000 sq. ft. this spring. No fertilizer should be applied after April 15. Late spring or summer applications will almost guarantee a brown patch disease problem in late May to July. Brown patch looks like circular patches of brown grass becoming more numerous and increasing in size killing large areas of turf in the process. Development of brown patch is further encouraged by hot, humid summer weather and irrigation at night. We can’t do much for the weather in Tennessee, but we can at least adjust irrigation and fertilizer before the disease has a chance to begin.

Crabgrass is major pest in many Tennessee lawns. Crabgrass begins germination when soil temperatures reach 55 degrees. The majority of growth however occurs during the hot temperatures of summer, when cool-season lawns are less competitive. Open, weakened turf areas also promote crabgrass infestations due to more available sunlight contacting the soil and weed seeds. Two important steps in a complete crabgrass control program include 1) maintaining a healthy turf and 2) preventing new seed production. Proper grass species selection, proper fertilization, maintaining correct pH levels, and correct mowing practices are all ways to promote a thick, healthy turf that will help shade and crowd out crabgrass seedlings. Herbicide treatments are an important step in preventing new seed production. However, since crabgrass and lawn grasses are closely related, pre-emergence treatments are the only way to effectively control this pest. In our area, the first application of a pre-emergent herbicide should be timed with the forsythia. When this shrub is covered with yellow blooms, soil temperatures are warm enough to encourage crabgrass emergence. Follow-up applications will vary by product, so be sure to refer to the label.

Although you may save time applying fertilizer and herbicides in a combination product, the problems associated with this method outweigh the benefits. For example, pre-emergence herbicides may need to be applied into late April or even May. If you’re growing tall fescue lawns, you’ll recall from earlier that fertilizer should not be applied later than April 15 to reduce the risk of Brown Patch. When fertilizing dates and optimum timing for weed control do not coincide, use separate products.

The downside to spring applications of pre-emergent herbicides is that it also prevents the germination of cool-season lawn grasses. However, since grasses germinate and establish better when applied in the fall, spring seeding is generally not recommended.

Perennial Flowers and Vines:

Sometimes it’s hard to recognize when perennials should be divided. Although there is not a set date, plants will often let you know if a division is needed. Common signals to watch for include: reduced flowering; smaller flowers; the interior of plant looks dead or has sparse vegetation; or the plant falls open. For most perennials, this will not occur until after 3 growing seasons, but for some it may take 8-10 years. If you noticed this problem during the summer, now is the time to divide your perennials. Some exceptions to the rule include peony and iris that are best divided in late summer or early fall. To divide perennials, begin by digging out the entire plant. Then, using a knife or spade, cut the clump into quart or gallon sized plants selecting healthy plants along the edge of the clump rather than the dead center. Use pruners to trim off any damaged roots. Keep your cuttings moist until planting, and then be sure to water after planting.

Ornamental grasses give many of the same signals when they are ready to be divided, but be prepared that large masses with a matted root system will require a lot of effort. Begin by cutting back grasses to just above their crown using grass cutters or hedge shears. Again, dig up the plant to make your divisions. Ornamental grasses may require an axe or wood saw, rather than a shovel, when dividing because of their thick root mass. Replant these cuttings quickly, since they will have a tendency to dry out fast.

One group of plants often under-used and under-appreciated in home landscapes are vines. This is unfortunate since vines can often fill spaces not practical for other landscape plants. Vines can provide a fast screen for privacy on your patio, hide unsightly views, and they can be grown on a pergola for quick shade or as groundcovers where lawns will not. In small gardens, they excel at adding the element of height and when covering and blending a structure with other plantings. Not only are vines useful but they also provide beautiful flowers, rich foliage, and sweet fragrance. In fact, vines may be one of the most versatile plants in the landscape.

Proper vine selection begins with careful consideration of the planting site. Vines used for screening should rapidly grow dense, evergreen foliage; fragrant vines should be placed close to windows or patios to enjoy; deciduous vines could be used for summer shade but allow light through in the winter; and a vine suitable for creative pruning may look great on a stone wall. Plant hardiness, soil adaptability, sunlight and type of support needed should also be considered. Vines climb by tendrils, by twining or by clinging. Tendrils are slim, leafless stems that wrap around most anything less than ½ inch wide. Grapes and some clematis are vines that climb using tendrils. These vines will need support to climb but this could be as simple as stringing wires on posts or walls. Twining vines use their main stem to wind around posts, trees, wires, or fences. Wisteria, morning glories, and honeysuckles are examples of twining vines. Clinging vines climb by attaching small rootlets (i.e. English ivy) or adhesive disks (i.e. Virginia creeper). Both types of clinging vines will grow on brick and masonry walls, but vines that cling with rootlets may actually damage the mortar on homes over time. Neither type of clinging vines should be grown directly on wooden homes since excessive dampness can occur that may lead to rot. If you truly want a vine to climb your home, try hanging a trellis on the wall and place spacers 2 to 3 inches thick on the back of the open latticework to keep vines away from the structure and allow for air circulation. Use twining or tendril vines to cover the trellis. Vines benefit from a rich, deep, well-drained soil. If you are adding organic matter, like compost, to improve your soil, be sure to incorporate it into the top 6 to 12 inches of the planting bed rather than just backfilling the planting hole. Water after planting and use a mulch to keep moisture in the soil. If growing vines next to a building, space the plant at least 18 inches out from the house to avoid the roof overhangs. Container-grown vines can be planted any time of the year, but bare-root vines are best planted during the fall and winter months. Fall and winter planted vines can be fertilized with a balanced fertilizer (about a tablespoon of 10-10-10) in the spring. Wait five weeks before fertilizing if you plant your vines in the spring. Established vines need 1 ½ lbs per 100 sq. ft. of 6-12-12 or 5-10-10 in early spring and mid-summer. As a general rule, flowering vines should be pruned after they bloom. Generally, pruning is only necessary to remove dead, diseased, and damaged wood, to reduce size, or to promote branching. However fast-growing vines like wisteria may require a great deal of pruning to keep them in bounds.

A note about vines — several ornamental vines have been identified as invasive exotic species in this area and should be avoided.  Those vines include English ivy, Chinese wisteria, Chinese bittersweet, Japanese honeysuckle, and Porcelain berry.   Native vine alternatives include Trumpet creeper, Carolina jessamine, Passionflower, Dutchman’s pipevine, and the native wisteria, honeysuckle and clematis vines.  And despite folk lore to the contrary, Virginia creeper is not poison ivy and will not cause skin irritation upon contact.

Plants in Pots:

It might be time to give your houseplants some TLC.  Reduced light indoors can cause spindly growth and foliage to fade to a pale green color or cause new foliage to be small and reduced in size. Conversely, too much light may sunburn leaves, cause them to wilt or become spotted. The following can be used as an abbreviated guide to summarize possible causes of typical symptoms often seen in houseplants.

  • New growth appears wilted or burned – sunburn, freeze damage, excessive fertilizer, extremes of temperatures, dry soil
  • Entire plant wilts – Too much or too little water, excessive fertilizer, cold damage
  • Spotted foliage – Excessive watering, excessive light, cold water on foliage (seen often in African violets)
  • Leaf tips turn brown – Excessive fertilizer, reaction to soil pH, low humidity
  • Lower leaves turn yellow and fall – Not enough light, too much or too little water
  • Foliage is light green in color – Not enough light, excessive light, dryness

Many houseplants can be easily propagated by cuttings. Cuttings are taken from a part of a parent plant and with proper care can produce roots and stems to form a new independent plant. There are many types of cutting methods and each method is specific to individual plants. Tip and stem cuttings are typically 3 to 5 inches long and are taken from the tip of plants just below a leaf. This method works well for Swedish ivy, Philodendron, Dracaena, Jade Plant and Christmas Cactus. Cane cuttings are used to propagate Dracaena and Dumbcane. Cut the cane into 2 to 3 inch long pieces and place these on their side barely below the surface of the rooting medium. A new bud will eventually sprout and form a new stem. Whole leaves can be used as cuttings for African Violet, Kalanchoe, and Peperomia. Leaves are placed in the rooting medium and new roots and leaves will form at its base. The Snake Plant can be propagated by leaf section cuttings. With this plant, leaves are cut into pieces, with the edge of the cutting closest to the base of the parent plant inserted into the rooting medium. Leaf bud cuttings consist of a leaf attached to a 1 inch piece of stem. On the stem lays a dormant bud that, once planted in your soil medium, will give rise to a new shoot and branches. Good choices for leaf bud cuttings include English Ivy and Peperomia. A mixture of half sand and half peat moss will hold moisture and prevent rapid drying and is an ideal rooting medium for use in homes. Horticultural vermiculite can also be used for rooting cuttings because it is sterile and holds moisture. Cuttings root more quickly in a moist, protected enclosure. One enclosed method would be to place a small amount of rooting medium in a covered glass jar or terrarium. You could also try placing three to four inches of moistened rooting medium in a plastic bag, inserting the cutting, and tying the bag closed with a twist-tie. With an enclosed method it will be unnecessary to add additional water.

If your houseplants became ‘leggy’ over the winter, it’s a good bet they did not receive enough light. Although we can improve light intensity by proper plant placement or additional lighting, sometimes it may be easier to change plants. One of the most durable house plants, tolerant of dimly lit homes, is the Chinese Evergreen (Aglaonema modestum). The Chinese Evergreen will grow to 3 feet tall and 3 feet wide at maturity. It is grown for its foliage which may be either solid green or variegated silver. The solid green cultivar tolerates the lowest light, while the variegated cultivar will need moderate light. This plant prefers temperatures between 68 to 77 degrees, but can survive at 55 degrees. Chinese Evergreen would prefer moist air but can tolerate the low to moderate humidity of most homes. Plant diseases are rarely a problem but can occur if plants receive too much or too little water. A poorly draining soil medium can lead to root rot and excessive fertilizer will cause leaf burn. There are several cultivars of the Chinese Evergreen however, ‘Silver King’ and ‘Emerald Beauty’ are very commonly found. Other species of Aglaonema include the Ribbon Aglaonema which has dark green leaves with gray marks and the Pewter Plant, a very robust plant with silvery markings. Aglaonema can be propagated by division or stem cuttings.

Vegetables and Herbs:

Unless soils are too wet, all of the following cool-season vegetable can be planted this month in Tennessee: Beets (best planted early in the month), Broccoli, Cabbage, Cauliflower, Carrots, Collards, Kohlrabi, Lettuce, Onions, Peas, Irish Potatoes, Radish, Swiss Chard, Turnips.

Vegetables cannot properly grow, unless the soil is adjusted for lime requirements and fertilized.  A soil test is your most reliable way of determining application rates. pH units are a measurement of soil acidity. Most vegetables grow best in soils with a pH of 6 to 6.8 (slightly acidic). For proper vegetable development, you will need to apply a complete fertilizer such as 10-10-10 or 15-15-15.  The first number denotes the percentage of nitrogen (N), the second refers to phosphate (P2O5), and the third number refers to potash (K20).  More organic methods using compost is certainly another way to provide your vegetables with important nutrients. Manure is another form of complete fertilizer, however the nutrient value varies according to source, storage, and moisture.  Manure may also carry weed seeds and herbicide residue, so use manure with caution.   Since manure is typically lower in nutritive value it may require a higher application rate for the same effect. Apply your fertilizers before planting, broadcasting across the plot or applying to rows. Work it into the soil first and then plant. Use caution not to over-fertilize since vegetable plants can be damaged. Vegetables with a long growing season will also benefit from side dressing. You can side dress with ammonium nitrate (34-0-0) or a complete fertilizer but rates will vary by vegetable. Tomatoes, Peppers and Eggplant need 1 tablespoon of ammonium nitrate per plant when the first fruits are 1 inch in diameter. Broccoli, Cabbage and Cauliflower will need ½ tablespoon 3 to 4 weeks after transplanting. The rates and application time vary with other vegetables. Check with your extension agent for more details.

If soils are not too wet, begin preparing your vegetable garden for planting. The best garden soils are rich in organic matter. Compost, well-rotted manure, or processed manure (mushroom compost) are good additives for building-up organic levels in the soil.

Early spring is great time to start planting cool-season vegetables like lettuce, spinach, or mustard. But if you’re looking for a vegetable with a unique taste, try rhubarb. This herbaceous perennial is a member of the buckwheat family and is great in pies, sauces, and other tart food items. It also is a good source of vitamins A and C, and has moderate levels of calcium and potassium. The petioles (leafstalks) are the edible portion and are available in red (Canada Red, Cherry Red, Crimson Red, Ruby) and green (Victoria). Plants are purchased as roots and should be planted while dormant with the crown bud 2 inches below the soil surface. Space roots 3 to 4 feet apart. A well-drained soil is a must for rhubarb to prevent rotting of the crown. Apply a complete garden fertilizer before growth begins in the spring and side-dress with nitrogen in late summer. You will not be able to harvest rhubarb during the first year of planting since newly set plants need their foliage to develop roots. A full harvest is not possible until the third season, but will last for 8 to 10 weeks. Follow the same fertilizer schedule each year and mulch the crowns with 6 inches of straw each winter after the soil is frozen. When harvesting rhubarb, carefully twist the petioles free from the crowns and remove the leaves. Do not eat rhubarb leaves as they contain toxic levels of oxalic acid. Remove only about one-third of the stalks from a single plant at a time. Extra rhubarb can be cut into small pieces, placed in plastic bags and frozen for later use.

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