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Month-by-Month Gardening Guide: April

Fruits and Nuts

Black and purple raspberries should be pruned just as buds break in the spring.  Shorten branches on the canes to 8 to 12 inches to promote branching. As new canes develop, maintain them at a height of 18 to 20 inches by tipping. This will promote branching and increase the stem diameter. After the crop is harvested, remove older canes at the soil line to decrease disease pressure.  Red raspberries do not branch well and should not be pruned during their first season’s growth.  Two year old canes can be topped at a height where they can support themselves and their fruit.  After the fruit is harvested, as with other raspberries, these canes should be removed at ground level.

Upright or erect-type blackberries should be pruned this spring, also.  As growth starts, remove any weak or dead canes and head side branches back to 12 to 18 inches.  Thin out sucker plants during the summer and tip new canes back to 24 to 30 inches to encourage branching.

If your apple trees were stricken with fire blight last year, expect it again this spring.  The brown to black scorched appearance of twigs, flowers, and foliage are the most recognized symptom of fire blight.  Later shoot tips often bend to resemble a shepherd’s crook.  Use streptomycin to control this disease, beginning applications at early bloom and repeating every 3 to 5 days until petal fall.  Avoid times when bees are most active.  Pruning out cankers and blighted shoots is a useful cultural control method. Cuts should be made 10-12 inches below the evidence of disease.  To avoid spreading the bacteria with your pruners, clean them with household bleach diluted 1:4 with water, after each cut.  Avoid excessive fertilizer and excessive pruning which promotes vigorous growth, which is susceptible to infection.

To avoid black rot in grapes, begin a rigorous spray schedule when new shoots are 2 to 4 inches long.  Repeat applications every 7 to 10 days until bloom.  This is a critical spray period to reduce rotting of some or all of the grapes in a cluster.  This disease is favored by warm, humid weather which is typically found in Tennessee.  Use Captan, ferbam or mancozeb with malathion.

Fire blight on apple and pear is a serious pest in central Tennessee.  The most noticeable symptom of this disease is the brown to black scorched appearance of twigs, flowers and foliage.  Shoot tips are often the first area attacked and frequently respond by bending into the shape of a shepherd’s crook.  The bacteria causing fire blight are carried by wind, rain and insects to blossoms or young shoots.  Control is somewhat difficult and requires an integrated approach.  Begin by planting varieties with resistance to fire blight.  These varieties may still be prone to the disease in warm, wet weather but the effects are often lessened.  Pruning out cankers and blighted shoots is a useful cultural control of the disease.  These infected areas will serve as a source for infection for healthy shoots.   Cuts should be made 10-12 inches below the evidence of disease.  To avoid spreading the bacteria with your pruners, clean them with household bleach diluted 1:4 with water, after each cut.  Also, fertilize your trees for moderate growth only.   Excessive fertilizer and excessive pruning will promote vigorous growth, which is susceptible to infection.  For chemical control, streptomycin is your best choice.  Apply at 1 teaspoon/gallon beginning when 20% of the blooms are open and continuing until petal fall every 5 days.  After petal fall, you can lower the rate and mixture according to label directions.  Remember that apple and pear are not the only fire blight susceptible plants you may own.   Landscape plants such as cotoneaster, crabapple, hawthorne, mountain ash, ornamental pear, firethorn, plum, quince and spirea may also serve as a source of infection.

Groundcovers and Lawns:

Make your first application of fertilizer to warm season grasses (i.e., bermudagrass, Zoysia) after April 15.  Use 1 pound of nitrogen per 1000 sq. ft. of lawn.  Phosphorous and potassium recommendations are best decided after taking a soil test.  You will want to follow-up with a second application of 1 pound of fertilizer on June 1.

Your last application of nitrogen fertilizer for cool-season lawns should be no later than April 15.  Use only ½ pound of nitrogen per 1000 sq. feet of lawn at this time to reduce susceptibility to Brown Patch.

Your first application of pre-emergence herbicide control of crabgrass should also been applied by this date, but don’t forget to make a second application four to six weeks later to knockout goosegrass.  This can cause a problem if you are using an herbicide/fertilizer combination on cool-season lawns.  Since your second application will occur after April, switch to a pre-emergent herbicide without the added fertilizer such as Surflan, Pendimethalin or Barricade.  Read the label for restrictions on lawns seeded last fall.

For warm season grasses, April 15 marks your first application of fertilizer. Use 1 pound of nitrogen per 1000 sq. ft. of lawn. Phosphorous and potassium recommendations are best decided after taking a soil test. You will want to follow-up with a second application of 1 pound of fertilizer on June 1.

Your first application of pre-emergence herbicide control of crabgrass should have also been applied by this date, but don’t forget to make a second application four to six weeks later to knockout goosegrass. This can cause a problem if you are using a herbicide/fertilizer combination on cool-season lawns. Since your second application will occur after April, switch to a pre-emergent herbicide without the added fertilizer such as Surflan, Pendimethalin or Barricade. Read the label for restrictions on lawns seeded last fall.

Perennial Flowers and Vines

One common question people ask about perennials concerns dividing.  When is the best time to divide and what’s the best way?  Although there is no rule as to when to divide perennials, some may be ready for division as early as 3 years and others as late as 10 years.  Some perennials should never be divided.  Lucky for us, perennials have a way of letting you know when it’s time.  Signals you should notice include: worn out or dead centers; smaller than normal flowers; stems falling over easily; bottom foliage is sparse; loss of vigor; or overgrowing its bounds.

Spring is a great time for dividing most perennials since temperatures are cooler and there is typically more soil moisture, which reduces plant stress.  Begin dividing a plant by digging around the plant and lifting out the entire clump.  Use a spade or sharp knife to cut the clump into quart or gallon sized divisions.  Each division needs to have three to five vigorous shoots.  Discard divisions from the dead center and any less vigorous portions.  Divisions should be kept moist and shaded as you prepare your planting site.  Divisions can be replanted immediately and should be watered in well.  This process works well for most clump-growing perennials (i.e., daylilies, Siberian iris, spiderwort).  Fleshy-rooted perennials (i.e., poppy, peony, iris) are best divided in late summer to early fall.  Other perennials such as hellebores, baptisia, and other woody-root plants are difficult to divide and better left alone.

A layer of mulch around your perennials this spring can help better prepare your plants for summer.  Mulch helps to regulate soil moisture and soil temperatures.  It also suppresses weed growth and improves the soil structure. Avoid applying mulch deeper than 3 inches.  Also be careful not to much around and over the plants’ crown as this can lead to disease problems.  Good options for mulch include compost, pine needles, shredded bark and pine bark.

More than any other ornamental plant, vines have a way of fitting the many special niches in your landscape.  If you are looking for color on arbors or walls, vines can do it.  If you are looking to screen unsightly views, vines can do it.  If you can’t get grass to grow in the shade, vines can do it.  If you need to provide privacy on patios (you guessed it) vines can do it.  Vines are one of the most versatile plants in the landscape and they can be easy to grow as well.  It all begins with selection.  Plan ahead and select vines according to their intended use, color of bloom, sun or shade tolerance and maintenance requirements.  This last one is especially important since some vines like wisteria and honeysuckle will need a lot of pruning.  Climbing vines also need different types of supports based on their growing habits (i.e. clinging, twining, winding).  Clinging vines hold to surfaces by means of rootlets or adhesive disks.  Because they may damage mortar or wood on homes these are best suited for arbors (ex. Virginia Creeper, Trumpet Creeper).  Twining vines encircle upright supports such as wires and lattice (ex. Morning Glory, Carolina Jessamine, Wisteria).  Winding vines climb by means of tendrils that wrap around their supports (ex. Maypop, Clematis, Trumpet Honeysuckle).  Most vines need well-drained, fertile soils.  If you need to amend your soil incorporate organic matter into the top 12 inches of soil before planting.  Dig the planting hole twice the width of the root ball and level the top of the root ball with the top of the soil surface.  If you plant this spring, wait several weeks (4-6 weeks) before fertilizing so the plants can get established.  Use a tablespoon of complete fertilizer such as 10-10-10 and sprinkle around the planting hole.

Bulbs, Corms, Rhizomes

Check for slugs around spring bulbs and emerging lilies.  These pests will climb stems and hollow out the daffodil blooms, or chew through a tulip stem.  Handpick slugs or use baits carefully.  You can also place boards on the ground overnight.  Slugs and snails will move under these boards during the day for shelter. Then you can turn over the boards and remove the pests.

Hand weeding around emerging spring bulbs will help eliminate competition for moisture and nutrients.  After pulling weeds, refresh the mulch around the bulbs to prevent new weed seedlings from emerging.  Water is especially needed during bud and foliage development.  If rainfall is insufficient, you may need to irrigate with a soaker hose.  Fertilize your bulbs to help increase bulb size just after flowering.  Use a complete fertilizer, such as 5-10-10 at a rate of 2 lbs. per 100 sq.ft.  As bulbs finish blooming, remove the faded blooms but maintain the foliage for up to six weeks for good bulb development and re-growth next season.  You can remove the foliage when it has yellowed and comes loose when slightly tugged.

If you noticed smaller blooms on your bulbs this year, it may be a signal to divide them.  After the foliage dies back completely, dig up the bulbs, separate, and re-plant them spaced further apart. You can re-plant immediately or store the bulbs and plant in the fall.

The most serious pest to iris is the iris borer.  It overwinters in the egg stage attached to leaves and begins hatching in late April.  The tiny caterpillars crawl up iris leaves and begin chewing and mining their way down within the leaf fold, eventually reaching the rhizome.  Once in the rhizome, they continue to feed, sometimes turning the rhizome to a hollow shell.  To reduce iris borer problems eliminate the eggs by removing and destroying debris and old leaves in and around the iris planting both spring and late fall.  Leaves can be treated in the spring with Dimethoate (Cygon 2E) for additional control. Make the first application when the new growth is 6 to 9 inches in height, then as needed to kill borers within them.

April is the beginning of the summer-flowering bulb planting season.  These are bulbs that will tolerate our summers but must be dug up in the fall before winter.  Most of the summer-flowering bulbs do best if planted in full sun. During April and May you can plant Anemones (windflowers) and expect flowers in May or June.  Lily-of-the-valley can be planted in the shade and makes a great groundcover since it spreads by rhizomes.  Since it is an exception to the rule, Lily-of-the-valley can be left out year round.  Dahlias are often planted as annuals but they can be dug up and stored as well.  These will bloom from June through October.

Spring blooming bulbs should be fertilized lightly this month.  Use 1 pound of 5-10-10 or 3 pounds of bone meal for each 50 sq. ft. bed.  Avoid high nitrogen fertilizers and don’t allow the fertilizer to stay on the foliage since this may cause burn.  Water is very important for bulbs to perform their best.  Springs are typically wet in central Tennessee, however if we experience dry periods you should water your bulbs to ensure survival.  Because some bulbs are planted as deep as 6 to 8 inches, a thorough watering which reaches this depth is required.  As with most garden plants, bulbs need about an inch of water per week.

You can remove faded flowers as they begin to die, but it’s very important to leave the foliage intact.   The leaves manufacture food that is stored in the bulb and without which your bulbs may not return the following year.  Allow the foliage to die naturally and remove leaves by hand-pulling rather than cutting to reduce disease problems.  Avoid tying leaves together since this practice reduces the amount of sunlight plants receive and the amount of food the bulb can produce and store.  If you find the yellowing leaves unattractive, try interplanting your bulbs with perennials like daylilies or spiderwort that partially hide the foliage.

Trees and Shrubs:

Flowering trees are a valuable asset to home landscapes.  One spring bloomer that performs great in our area is our native Redbud (Cercis Canadensis).  This small tree explodes with rosy pink blossoms in early spring which persist up to three weeks.  The blooms are most often the first reason people select this tree.  When in full bloom, flowers nearly cover the leafless branches and may occasionally appear on the trunk.  The tree’s full heart-shaped leaves emerge near the end of the blooming period.  Another good trait of redbuds is their small height.  Maturing at less than 30 feet tall makes this tree a good choice near utility lines.

Redbuds develop with a wide crown and often look best when bordered by evergreens or woodlands.  Although redbuds can tolerate full sun, they perform best when they receive some shade during the hottest part of our summer days.  Their seedpods, which resemble peas, are produced in late summer.  Just as redbuds come into spring with a bang; many would agree they are just as impressive with their bright yellow display of fall color.

When selecting a planting site, look for moist, well-drained soil.  Redbuds should be purchased from a nursery rather than dug from the woods since they don’t transplant easily and may exhibit shock when moved from a wooded environment to an open landscape.  Redbuds grow at a moderate rate but are considered a short-lived tree, often declining from canker after 20 years.  Other than this disease, they are considered a relatively pest free tree.  To discourage canker, keep string trimmers and mowers away from the trunk by applying a 2 to3 inch layer of mulch around the base. There are many cultivars and varieties of redbud available. The following are the most common:

var. alba – a white-flowered form
‘Royal White’ – larger flowers and more compact than var. alba
‘Forest Pansy’ – deep burgundy foliage; rose purple blooms
‘Flame’ – double-pink blooms
‘Silver Cloud’ – variegated pink and white leaves

Although the majority of shrubs do best when pruned in late fall or winter, spring-blooming shrubs such as forsythia, spirea, and rhododendron are pruned when they bloom or immediately after blooming.  These shrubs form next year’s buds in early to mid-summer so timing is critical to avoid loss of blooms next year.  Roses have different pruning needs according to their variety.  Repeat blooming roses such as floribunda and hybrid tea roses benefit best from a heavy pruning every spring, just as the buds break dormancy.  The best way to judge when to prune is to look at the buds; when they begin to swell, go ahead and prune.  Old-fashioned roses and climbers bloom once a year and should be pruned immediately after flowering.  They bloom on wood from the previous year’s growth and should not be pruned in the spring.  Dead, diseased or damaged wood on any rose, tree or shrub can be pruned out at any time.

Tents of the Eastern Tent Caterpillar are a part of the landscape in many trees, especially in subdivision developments in rural areas.  The favorite host plants of the caterpillar are wild cherry and apple trees, but they will also feed on peach, plum, hawthorn and many different shade and forest trees.   These pests are voracious feeders and can completely defoliate small trees.  We usually identify these caterpillars by the web it constructs in the crotches of limbs.  These webs will enlarge as the caterpillars grow and can become several layers thick.  We can exhibit some control of this pest on small trees and where webs are few by hand destruction of the webs or pruning of host limbs. However, better control can be achieved before the webs occur.  The caterpillar will hatch from egg masses encircling small branches that were laid by the moths late last spring.  The eggs hatch about the time when the leaves first begin to come out.  Application of an insecticide at this time will provide good control.  Many insecticides labeled for ornamental use will control this pest.   If you use Bt (Bacillus thuringiensis), remember to spray the foliage because the caterpillars need to ingest the Bt for it to work.

Vegetables and Herbs:

One of the biggest pests to vegetable gardens are weeds.  Not only do weeds attract other pests, like insects, and provide hiding areas for mice and other rodents that may feed on tender plants, they also compete for water, nutrients, sunlight, and growing space.  If left unchecked, weeds can significantly reduce vegetable yields. Weed control is especially important in the early stages of vegetable development.   Methods of control include: cultivation, mulches, and herbicides.

Cultivation (hoeing, tilling, hand pulling) effectively removes many annual weeds but may not completely remove perennial weeds.  When cultivating the soil, remember shallow tillage is best.   Deep cultivation pulls new weed seeds to the surface where they are exposed to light and can germinate into new plants.  Use a hoe in rows and hand pull weeds next to crops to avoid root damage to vegetables.  This process is most effective if plants are removed before they have a chance to set seed.

Mulch can also be used around vegetables to suppress weeds.  Additionally, mulch helps to regulate soil moisture, reduce erosion, and keep fruits and vegetables clean which may reduce disease problems.   Shredded leaves and pine straw are good choices and should be applied after the soil has begun to warm in the spring but after existing weeds have been removed.

Finally, herbicides, if used according to the label, can be effectively used to control weeds.  Pre-emergence herbicides such as Preen, Treflan, and Miracle Gro Garden Weed Preventer are used before weed seeds germinate.  These products may not be safe around all vegetables and you should refer to the label for specific information.  Remember that these products kill newly emerging seeds, which includes vegetable seeds.   Be sure to follow any waiting periods listed on the label.  Round-up is a post-emergence, non-selective herbicide.  It is absorbed by any actively growing plant.   Still, it can be used to control difficult weeds if you take caution not to allow spray to drift onto your vegetables.  The label lists specific vegetables around which this product can be safely used.

Did you get your cool-season vegetables set out last month?   If you didn’t, fear not.  All the ones listed for March will have plenty of time to develop and mature before the summer heat if you plant them by the end of April.  You can also begin a few of the warm-season vegetables this month such as bush and pole beans, sweet corn and tomatoes.  Be mindful of any late frosts that can damage new seedling or slips.  In Chattanooga, the last frost date is around April 17.  However, in higher elevations like Signal Mountain and Lookout Mountain, frost may occur even later, so waiting until the end of the month or the first of May would be suggested.
• If you do set out tender slips or have new seedlings up when a late frost is expected, cut the bottoms out of gallon milk jugs and place them over your vegetables to give protection. It is very important though to remove the container during the day to protect the plant from overheating.

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