Dear Master Gardener: Are the leaves of the horseradish plant edible or poisonous?

Answer: Recipes for preparing horseradish leaves (Armoracia rusticana) are out there, but so are warnings about their toxicity. According to Susan Mahr at the University of Wisconsin Extension, "the leaves are edible raw or cooked, but rarely eaten." Both Montana State University Extension and Oregon State University Extension list the leaves of the horseradish plant as poisonous. According to North Carolina State University Extension, the edible parts are the roots, which are used as a condiment, but only in small amounts; and the leaves, as they expand in the spring, which may be boiled in salted water until tender, then eaten with butter or margarine. NC State Extension also states,"Horseradish is only toxic if large quantities are eaten."

Horseradish plants belong to the Brassica family, so their leaves, as well as the roots, produce glucosinolates, which are the enzymes that give the roots their spicy flavor. In large amounts, these enzymes might be toxic, but in most cases, eating horseradish is safe.

Dear Master Gardener: I would like to make a privacy screen by creating a living wall using vines. This is for my home in the Cities and unfortunately the area gets little to no direct sunlight. Is there a vine I can plant that can tolerate this much shade?

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Answer: Growing vines on a trellis is a way to provide some privacy in outdoor spaces. Many screening plants are highly ornamental with attractive flowers, foliage or fruits. There are two vines that will do well in full shade and make excellent screens. Boston ivy (Parthenocissus tricuspidata) is a zone 4 plant that creates a screen and has red fall color. Your trellis needs to be very sturdy to support the weight of this vine. The other vine, Englemann ivy (Parthenocissus quinquefolia) is a popular, tough vine that is hardy to zone 2b. Englemann ivy has large, dark green, five-lobed leaves that have outstanding red and purple color in fall. One thing to keep in mind is that ivies should not be grown directly on exterior walls and brick chimneys to prevent damage to the siding or mortar.

Dear Master Gardener: Is it better to grow onions from seeds or sets?

Answer: Onions can be direct seeded or grown from transplants. If you are going to direct seed, do it as soon as the soil can be worked. Sow seeds in a two-inch wide band, one-fourth to one-half inch deep, in rows 12-18 inches apart. After seedlings emerge, thin to three to four inches apart. If you purchase transplants, they can be planted when temperatures reach 50° F. Plant them pointy end up, about two inches deep and three to four inches apart. They can tolerate a light frost. Onions can also be planted from sets. Most of the sets available from local stores in Minnesota are of the short day type and will usually get as large as long day onions. If using sets, plant them as soon as possible in the spring.

April Garden Tips

• Direct seed early vegetables into the garden as soon as the soil has dried enough to work easily and the soil has warmed to about 40 degrees. Leaf lettuce, onions, radishes and garden peas can take cool soil and air temperatures.

• Plant tomato seeds indoors at the beginning of this month. They need six to eight weeks indoors under lights (ideally) or in a sunny window before they are large enough to transplant into the garden. Putting out really big plants or getting them out too early, when the soil is still cool, will only set the plants back and potentially reduce their yield. Wait until the soil temperature reaches 60 degrees to transplant your seedlings.

• Plant pansies, violas and johnny jump-ups outdoors once they are available from garden centers (late this month or early May). If you put them in pots you can bring them into your garage if hard frost threatens. They will withstand light frost with no problem. Deadhead faded flowers to promote best blooming.

• Begin to remove protective cover from bulb beds, non-hardy roses, and perennials, in stages as soil and mulch thaw. Don't be in too big of a hurry to uncover tender plants because mulch helps prevent them from coming out of dormancy too early, when damaging cold is still a possibility. Rose canes will be alright as long as temperatures stay around 20 degrees; most flowering perennials will die back when it's that cold.

• Don't be tempted by those glossy ads you might see for "miracle" plants; such as zoysia grass plugs, tree tomatoes, princess trees, "hardy" peaches, and others. They are a waste of money. Buy from reputable local nurseries or garden centers and legitimate mail order sources.

• Keep foot traffic on your lawns to a minimum. Wait until the soil feels firm under foot and is no longer moist and spongy so you don't compact the soil and make it harder for grass to grow and easier for weeds to take over. Wait even if you have patches of snow mold in the lawn-use a lightweight rake to break it up later, but minimize walking on the lawn. Hold off fertilizing until the grass is growing actively and you have mowed a few times.

• Wait to prune out winter-burned sections of arborvitae until new growth begins to expand because it may mask the browned foliage. Junipers, yews, pines and spruce put on new growth at the tips of the branches later in spring. Don't prune way back into older wood. There is no guarantee that evergreens will develop new growth at that site and the branch may eventually die.

• Start a compost pile! Keep the pile moist and turn it frequently to maintain the aerobic breakdown processes.

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University of Minnesota Extension Master Gardeners are trained and certified volunteers for the University of Minnesota Extension. All information given in this column is based on university research. To ask a question, call the Master Gardener Help Line at 218-454-GROW (4769) and leave a recorded message. A Master Gardener will return your call.