Saturday, March 30, 2013

Spring in Full Swing?

It may not seem like it, but spring is actually in full swing in gardens around the Tennessee Valley region. Our neighbors up in the mountains can expect a few more weeks of cold weather, but here in the Valley the forecast is for a warming trend. With the onset of warm weather delayed this year, we are experiencing a more nearly normal progression of blooming plants. An early spring tends to cause everything to bloom at the same time. Take heart, therefore, that the cold weather means a longer bloom season.

Next Saturday, April 6, is the annual UT Gardens Spring Plant Sale. Open from 9:00 AM to 2:00 PM, the sale features many new plant varieties. Shoppers should arrive early in the day for the best selection. Among the many interesting plants to be offered is the world's largest hosta, 'Empress Wu.' Producing a huge clump of leaves almost 5 feet tall and wide after a few years, this plant would make a great focal point in a shady, moist location.

Our Plant of the Week this week is that old stand-by, Forsythia. With its fountain of long stems bearing deep golden yellow flowers every spring, this passalong shrub has been cultivated for over 100 years. It hails from Asia, but adapts to most soils, as long as it receives full sun. Dr. Sue and I both think forsythia looks best when given plenty of room and allowed to develop its natural shape. The worst thing you can do to one is give it a "crew cut."

Vegetable gardeners can plant beets, carrots, leeks, radishes and scallions between now and April 10. Later in the month is a good time to plant an early crop of beans. For best results, choose a bean variety with brown, rather than white seeds. Brown seeds seem to germinate better in cool soil. Pole or bush beans planted in April will produce a good crop before the heat of summer stresses them and invites bean beetles to lunch. Good Friday is the traditional time to plant beans in East Tennessee. I prefer to wait until around the frost date of April 15, this year more than two weeks after Good Friday.

Salad greens can be replanted in succession from now through the end of April. As the season progresses, choose more heat tolerant varieties. Black Seeded Simpson is a popular traditional lettuce cultivar. Plant it along with scallions, and in about six weeks you will have the makings of one of spring's great garden pleasures, Spring Salad with Hot Bacon Dressing. (For the recipe, visit our In The Kitchen Page.)

Broccoli and cabbage plants can go into the ground any time from now until around April 20. You want them to have time to mature before the nights get too warm. Keep caterpillars at bay with row covers and/or regular dusting with Dipel. Dipel is a harmless, all natural bacterial pesticide that can be used right up until the day before harvest. It is effective against a variety of caterpillars.

If you are planning on adding fruit trees, berry bushes, or strawberry plants, time is running out for bareroot stock. Containerized plants can be moved any time, but will do much better if transplanted early. As a general rule, if the plant is available at your local garden center, you can go ahead and place it in the garden.

Now is a good time to start your tomatoes for late spring transplants. The seeds germinate best between 75 and 85 degrees. Beware of cooler temperatures, which will delay germination, weaken the seedlings and encourage damping off. We like to sow tomatoes in 72-cell trays and transplant to small pots when they have two pairs of true leaves. One great thing about tomatoes, if you start them too early, they will hold very well in containers until you can get them in the ground. Just be sure to transplant to roomy pots so they can develop a good root system.

Peppers and eggplants should wait until the frost date, although you will see them in the markets earlier than this. In my experience, planting too early will lead to smaller pepper plants and encourage flea beetles to attack eggplant. Wait until the soil is 65 degrees or warmer before planting either of these crops.

Saturday, March 23, 2013

Redbuds - The "Perfect" Tree

Our Plant of the Week on "Garden Talk" this week is the eastern redbud, Cercis canadensis. After discussing this tree with co-host Dr. Sue Hamilton, Nancy Schneider (woody plant specialist at Stanley's Greenhouse) and UT horticulture student David Pease, I have concluded it must be the "perfect" small tree for the Tennessee Valley region.
Besides welcoming spring with its display of pink blossoms, the eastern redbud offers the gardener many advantages. It grows easily in most soils. Because it is a legume, it actually helps to build the soil underneath it, by fixing atmospheric nitrogen with the help of bacteria living on the roots. Although tent caterpillars sometimes find the tree tasty, they are generally easy to control. The redbud has few other insect pests. Older trees are susceptible to trunk canker, a fungal disease that eventually kills the tree, although many specimens endure for a long time before succumbing to this problem. Otherwise, redbuds are carefree.

Transplant redbud trees from late fall until early spring. Container grown specimens typically bloom the year they are transplanted. Set the plants slightly higher than the surrounding soil, in order to avoid covering the crown. Water in and mulch. Irrigate if rainfall is insufficient. After the first season, the tree will be much more drought tolerant. Fertilization is not needed and may reduce bloom. Adaptable to many soil types, the redbud does best in well-drained, moisture retentive soil with organic matter.

Redbud trees grow easily from seeds, which are borne in pods that look like small snow peas. As a result, many cultivars and selections exist. Some of these are:

  • 'Alba' -- a white-flowered form (f. alba) that comes true from seeds, sometimes incorrectly sold as 'Texas White"
  • 'Dwarf White' -- another white-flowered redbud, it remains under 10 feet tall
  • 'Forest Pansy' -- with new foliage that is deep burgundy red, this variety blooms later than the wild type
  • 'Silver Cloud' -- white leaf variegation on a tree that prefers light shade
  • 'Pink Heartbreaker' -- a weeping form that does not need staking to remain upright
  • 'Covey' -- a dwarf weeping form that grows upright only if staked; unstaked plants will sprawl and become a ground cover

Besides our native eastern redbud, other species are sometimes available in garden centers. These include the western, or California, redbud (C. occidentalis) and the Chinese redbud (C. chinensis). The California redbud forms a multi-stemmed shrub when grown in the Tennessee Valley and is more sensitive to trunk canker than the eastern species. Chinese redbud is resistant to trunk canker, but grows much larger than the North American species, about 40 feet.

Flowers of the redbuds are edible. Native Americans used redbud for medicinal purposes. The flowers can be fried in batter, or mixed with nuts and honey or chopped dried fruit. Flower buds may be pickled like capers, and the green seed pods can be used much like snow peas in sautes and stir-fries. Honeybees and other pollinators are attracted to redbuds, and the eastern redbud is the host plant for Henry's elfin butterfly (Callophyrus henrici).

Friday, March 15, 2013

Save the Monarchs!

One of the many pleasures of gardening is watching the butterflies that visit our flowers. Like so many other wild things, our local butterflies appear to be in trouble. The number and variety of species that I see dwindles each year. There has been a noticeable shift from larger species, such as the fritillaries, to smaller, more nondescript one, such as skippers. This shift may reflect the shift in vegetative cover in this area from deciduous woods to open fields, and the loss of habitat to development.

Yesterday, a disturbing report  revealed that the population of monarch butterflies (Danaus plexippus) has crashed in the last decade. Mexican scientists report that wintering populations that previously covered 50 acres of trees this season covered only 3 acres. Several possible reasons for this sharp decline, all related to human activity, have been proposed.

One explanation for the serious decline in the numbers of this beautiful butterfly may lie in the severe summer heat and drought that has been experienced in the central and southern states in recent years. The unusual weather patterns may result from climate change.

Another possible factor is the loss of habitat in Mexico, where the butterflies spend the winter, due to logging.

A third possibility is the widespread use of GMO crops, specifically "Roundup Ready" soybeans in the United States. The genetically engineered soybeans are unaffected by the herbicide, glyphosate, making it possible for farmers to almost completely eliminate milkweed from their fields. Milkweed is the food plant for the monarch's caterpillar. Adult monarchs feed on a variety of nectar plants, but the caterpillars will only survive on milkweeds.

Tennessee has 13 species of milkweeds, including butterfly weed (Asclepias tuberosa), swamp milkweed (A. incarnata) and common milkweed (A. syriaca). These three are often available in garden centers that carry native plants. Several of our other species have showy flowers and could be valuable garden plants, also. Milkweed seeds germinate readily and the plants are easy to care for, in my experience. Many have a pleasant fragrance, as well.

For a small donation, you can receive milkweed seeds appropriate for planting in your garden from this web site, LiveMonarch.com

Our local garden centers, including Stanley's Greenhouses, Ellenburg's Nursery, and Mayo Garden Centers, all offer Asclepias plants among their perennials flowers. You can also often find a tropical species, A. curassavica, which won't overwinter here but will charm you with its fiery red and yellow blooms.

Milkweed seed pods are among the most familiar sites along our back roads in late summer and early fall. You can harvest a few seeds from wild plants and grow them out at home. Wait until the pod has split and seeds are being released to collect them. Sow immediately outdoors, marking the spot well, and look for seedlings the following April or May. Transplant them to their permanent location, water well, and wait. They will bloom in their second or third season, depending upon the species and growing conditions.

Appropriate growing conditions for milkweeds depend on the species. Swamp milkweed, as you might guess, likes moist places. I see the flowers shining among other types of foliage in roadside ditches that hold water. Butterflyweed, on the other hand, likes dry, sharply drained sites. I have seen beautiful specimens growing out of crushed limestone fill on roadside embankments. Common milkweed seems to prefer average moisture and soil conditions, no doubt accounting for its widespread distribution.

This spring, why not add a few milkweed plants to your garden to help feed the monarchs?

Saturday, March 9, 2013

Countdown to the Equinox

Our special guests on "Garden Talk" this morning were Lisa Stanley of Stanley's Greenhouses, and UT student David Pease. We had a great discussion about our Plant of the Week, Magnolia stellata, the star magnolia and its cultivars and hybrids. David also shared insights about sweetshrub, or Carolina allspice, Calycanthus floridus and its hybrid and cultivated forms. Either of these shrubs would be a welcome addition to the landscape, and both reach about the same size, typically around twelve feet in diameter.

Tomorrow we switch to Daylight Savings Time, and it is only ten more days until the vernal equinox, March 20. Spring gardening tasks will become ever more numerous as the days lengthen and temperatures warm.

Now is just about the last opportunity to plant asparagus this year. Look for one-year old roots in your favorite independent garden center. Old timers will remember the cultivar 'Martha Washington' as the standard, but plant breeders have improved on this old standby. A more modern asparagus variety is 'Jersey Giant.' Seeds of this strain of asparagus produce 95% male offspring. Male asparagus plants are more productive than females because they do not invest energy in flower and seed production. The absence of seeds also means that volunteer seedlings, typically of inferior quality, will not crowd out your original planting.

Asparagus needs rich soil high in organic matter. A shovelful of well-composted manure (you can buy this in bags at many garden centers) should be placed beneath each crown you set in the bed. Dig down about five inches, add the compost, and place the crown on top, spreading the roots out as much as possible. Take care not to damage any developing shoots. Cover the plants with a layer of garden soil and water in well. Two weeks later, add another inch of soil. Continue adding more soil over the next few weeks until the planting site is slightly mounded. Keep the plants well watered and side dress with compost tea or a balanced organic fertilizer. Mulch to control weeds and remove any that do appear.

The key to success with asparagus lies in the treatment it receives during the first two years. Irrigation will be necessary to keep the plants growing well when rainfall fails, and each spring and fall the plants should be side dressed with a balanced organic fertilizer. Do not harvest any spears during the first growing season, and harvest sparingly during the second. Thereafter, the plants will be well-established and you can harvest at will.

Leave the foliage in place until late winter, then remove and burn or discard it to help control insects that may overwinter in the dead foliage.

A caller from Lee County, Virginia, this morning asked about growing vegetables in very rocky conditions. We suggested placing large containers here and there among the boulders and growing veggies in these, rather than trying to remove all the stones from a large plot. Container vegetable growing is a great way to utilize space that you might not otherwise consider for food crops. Always use a good potting mix, water regularly and choose plant varieties that remain small enough or adapt well to containers. Some of the best choices for container growing are lettuces and other greens, radishes, tomatoes, peppers, and bush beans. With the addition of a trellis, you can also grow peas and cucumbers in container gardens.

Saturday, March 2, 2013

A Winter Blooming Tree

On this morning's edition of "Garden Talk" on WNOX-FM 100.3, our featured "Plant of the Week" was one I have little experience with, but plan to acquire. I am referring to the Japanese  cornelian cherry and European cornelian cherry. Despite their names, these are both dogwoods, botanically Cornus officinalis and Cornus mas, respectively. The plant pictured in the image is the Japanese variety, C. officinalis, and it blooms just a bit earlier than C. mas. In particular, this specimen--which is growing at UT Gardens and is brilliantly visible to passing drivers along Neyland Drive--is a cultivar developed right here in Knoxville by nurseryman Mike Stansberry of Beaver Creek Nursery. Appropriately, its name is 'Sunsphere.' As you will note it has a short trunk, a rounded shape and literally covers itself with blooms. In these species, the bracts, which are the showy portion of our native dogwoods, are smaller than the yellow flowers. To give you an idea of the size of this plant, the concrete sculpture visible behind it is about 6 feet tall. Maximum height is 12 feet.

The surprising feature of this dogwood is its edible fruit. The "cherries" are 1/2 to 3/4 inch in diameter and should be picked and allowed to ripen off the tree for four or five days before consuming them. Ripened fruit reportedly tastes much like cranberries, and is rich in phytochemicals and anti-oxidants. We concluded in our discussion this morning that they should make excellent jam. The only problem, as with regular cherries, is keeping the birds from getting more fruit than you do.

The cornelian cherries need full to part sun, well-drained but moisture-retentive soil, and little else to thrive in East Tennessee. The spot where this plant is growing is slightly elevated above a drainage swale on the southwest side of the gardens.

Using these dogwoods in the landscape seems like a no-brainer, provided you have room for a smallish tree. They begin the dogwood season at the end of February, provide edible fruit and exhibit fall color ranging from golden yellow to purplish red. Given that they are carefree once established, these trees should be more widely used in our area.