Q&A with Bob Polomski 21

Extension Consumer Horticulturist, Clemson University

Several gardening books recommend using leaf mold as a soil conditioner. What is this, and how is it made?–B.M., Eldred, NY

Answer: Leaf mold is made up of partially decayed leaves. It is a natural product of woodlands where leaves accumulate and decay on the forest floor. To make it at home, rake up fallen leaves and corral them in a cylinder of snow fencing, chicken wire, or hardware cloth. Without any further attention, the leaves will turn into leaf mold in a couple of years.

You can speed the process by shredding the leaves with a lawn mower or shredder prior to piling them up. Since leaves are high in carbon, adding a nitrogen source will also hasten the composting. Half a cup of fertilizer with a 10% nitrogen content per 20 gallons of packed leaves will do the trick, as will turning the pile periodically to ensure that it is evenly moist and well aerated.

Whether you allow slow-acting fungi to do the decomposition, or let fast-acting nitrogen-consuming bacteria break down the organic matter, there is no need to add any starter cultures. The dead leaves are already inoculated with the necessary organisms.

The leaf mold that results will be dark and crumbly. It can be applied to the soil surface as a mulch or incorporated into the soil, where it will improve the organic content, the moisture-holding capacity, drainage, and tilth.

I'm looking for some ornamental crab apples that will provide winter interest Can you suggest any varieties for my area?–K.K., Winchester, IN

Answer: Since the springtime floral display of flowering crab apples (USDA Zones 4–8) lasts only a matter of weeks, you're wise to select crab apples for their fruit, which can persist through the winter to early spring before they are shed or eaten by birds. These fruits range from pea size to two inches in diameter (those that are greater than two inches are considered apples). Their colors range from green to yellow, orange, and red.

Other important ornamental features include flower color and fragrance, fall foliage color, attractive bark, and growth habit, which can be upright, spreading, or weeping.

Perhaps your first consideration in selecting any crab apple should be apple-scab resistance. Recent breeding efforts and evaluation programs have yielded many disease-resistant selections.

The following crab apples have persistent fruits as well as a high scab resistance: white-flowered ‘Bob White’, with yellow-gold to orange-gold fruit; white-flowered ‘Red Jewel’ and ‘Sugar Tyme’, both with cherry-red fruit; and ‘Prairifire’, with coral-red flowers that give rise to purplish red fruit. In addition, ‘Bob White’ and ‘Prairifire’ are both resistant to Japanese beetles.

Crab apples tolerate a range of soil conditions, but require full sun for their best fruiting display. They range in height from 10 feet to 25 feet, with an equal spread. Before you plant a crab apple, learn its ultimate size at maturity, so you can plant it in the right location. Generally, small cultivars need at least 150 square feet and larger ones need a minimum of 300 to 500 square feet.

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If you purchase grafted trees, be aware that some rootstocks have a tendency to produce suckers. (Crab apples grafted onto MM 111 rootstocks have relatively few suckering problems.) Alternatively, select trees on their own roots.

For more information about crab apples, visit the Web site of the International Ornamental Crabapple Society, www.malus.net.

I grow my African violets on a windowsill, but they aren't faring very well, especially during the winter months. What exposure do they prefer? Can I grow them under lights? –C.P., Madison, SD

Answer: African violets are day-neutral plants, which flower regardless of the season, provided they receive the right quality and intensity of light. During the spring and summer months, keep them in a west-facing window. During the fall and winter, move them to an east- or south-facing window. Avoid direct sunlight at all times. To compensate for the shorter days of winter, you can supplement natural sunlight with fluorescent lights. Use an automatic timer to turn the lights on and off, so your African violets can receive an additional five or six hours of light near the end of the day. They should receive between 12 and 16 hours of light daily, and no more than a total of 18 hours of light per day.

Alternatively, African violets can be grown exclusively under fluorescent lights. Their flat, rosette growth habit makes them ideal subjects for growing under lights. Suspend a pair of 48-inch-long, 40-watt, cool-white fluorescent tubes in a fixture equipped with reflectors, about a foot above the plants. Fixtures with four 40-watt tubes should be placed one to two feet above the plants, Periodically rotate the positions of the African violets to provide them all with fairly equal amounts oflight. Some growers recommend using a combination of warm-white and cool-white tubes; and still others like to use horticultural bulbs such as Gro-Lux or Veri-Lux. Experiment to see which are best for you. For more information about growing and collecting African violets, become a member of the African Violet Society of America (www.avsa.org).

I've recently moved up North and miss my southern plants. I know I can grow them as annuals, but I would like them to survive winters outdoors. Is there anything I can do to improve their hardiness here in Zone 6?—D.C, Meiserville, PA

Answer: Professor David Francko, the chair of the department of botany at Miami University in Oxford, Ohio (USDA Zone 6), has recently written a book entitled Palms Won't Grow Here and Other Myths: Warm-Climate Plants for Cooler Areas (Timber Press, 2003). To improve a tender plant's chance of survival, he says, start by identifying warm microclimates in your landscape. These “heat islands” can be on the south-facing side of your home, at the foot of a stone wall, or in nooks among large rocks. Look for areas that are well drained, especially during the winter months. These areas can be half a zone to a full zone warmer than their surroundings.

When you have found a promising location, mount a thermometer on a stake, one to two feet above the ground. Record the temperature right before the sun begins to rise, which is the coldest time of the day, and compare this to temperatures elsewhere in your yard. This will allow you to determine the warmest locations for planting.

In addition to planting in locations with a favorable microclimate, you can push a plant another zone by providing winter protection. One simple way to do this is to add a 6- to 12-inch layer of mulch for the winter, to protect the roots and lower stem. Also, enclosing evergreen foliage in burlap will protect it from winter leaf scorch. During especially severe cold snaps, you can cover plants with a cardboard box or drape a sheet or blanket over them. Remove this covering after a few days.

Along with providing protection from cold temperatures, prepare your plants for winter by making sure that they are well watered in the fall. Evergreens may need to be watered during the winter, especially when snowfall is absent. Also, avoid pruning your plants during the fall and winter months. Wait until after the coldest part of winter has passed before cutting back any winter-killed shoots. An exception to this rule are palms, whose cold-damaged fronds should be pruned back immediately to protect the crown from decay.

For two years, I've tried growing annual poppies from seed. Each time, I sow several packets of seed, but the results are always disappointing. What am I doing wrong? –M.F., Lamar, LA

Answer: A number of poppies can be grown as annuals. Corn poppies (Papaverrhoeas), which include a strain known as the Shirley poppy, are excellent, as are the Iceland or arctic poppy (P. nudicaule), scarlet Flanders poppy (P. commutatum), and the California poppy (Eschscholzia californica).

All these poppies resent root disturbance, so they should either be directsown or carefully transplanted from containers. In USDA Zone 7 and warmer, the seed is best sown in early fall. This tends to produce stronger plants than early-spring-sown seeds.

Choose a well-drained location that receives at least six hours of sun. Cultivate the soil and rake it smooth. Then mix the small seeds with grit (two parts seed to one part grit), to sow them evenly and to avoid overcrowding. Leave the soil surface bare or use a very light mulch. The seed should germinate in about two weeks in cool soil. Thin the seedlings to six inches apart. H