Hardy to USDA Zone 3, horseradish (Armoracia rusticana) is an herbaceous perennial native to eastern Europe and western Asia. It is grown for its thick taproot, which is grated to add pungency to sauces, relishes, and salads. A member of the mustard family (Brassicaceae), horseradish can spread aggressively in rich, loamy soil. You can control this tendency by harvesting it annually.

Annual harvesting also benefits flavor: Horseradish roots tend to lose their intense flavor and get stringy if left in the ground for more than one season. Harvest horseradish each fall after a few sharp frosts have stimulated the plant to begin storing starch in its roots. Dig up the entire plant and remove the foliage and any side roots. Sturdy six- to 12-inch-long side roots can be stored in moist sand or sawdust in a cool area over winter and planted the following spring.

Plant root cuttings two feet apart and four to six inches deep in fertile, well-drained soil and full sun. Set the cuttings at a slight angle in the soil, making sure the bottom end of each cutting is oriented downward. Horseradish should be included in a regular crop rotation to reduce the build-up of the soil-borne pests and diseases to which the mustard family is susceptible. Water regularly as needed during the season; the roots become woody if subjected to prolonged dry spells.

Karan Davis Cutler, author of Burpee’s Complete Vegetable and Herb Gardener: A Guide to Growing Your Garden Organically (Macmillan, 1997), recommends grating and storing in the refrigerator only as much horseradish root as you will use in a month. The ungrated portion of the root can be stored in damp sand in a cool, dark location or in a perforated plastic bag in the refrigerator for up to three months.

I have Joe-Pye weed in my garden that needs to be cut back. Although the roots are fairly close to the surface, they are thick and tough and I am having trouble getting them out. Do you have any suggestions? —S. C., via e-mail

Joe-Pye weed is the common name for several plants in the genus Eupatorium. The most commonly grown species are common Joe-Pye weed (E. purpureum), hollow Joe-Pye weed (E. fistulosum), and spotted Joe-Pye weed (E. maculatum).

A member of the daisy family (Compositae), this bold North American native perennial grows five to 10 feet tall—depending on species or cultivar—and up to five feet in diameter. Joe-Pye weed makes an architectural statement in the garden, and its clusters of purple flowers attract butterflies.

Joe-Pye weed can be dug and divided annually, preferably in the fall, to prevent its root system from spreading too far from the parent plant or plants. There is, unfortunately, no real short cut to the digging process. Digging should become easier if you retain one main stem and dig and divide the plant every year.

If digging is not feasible, prune back unwanted new growth as soon as it appears in spring, or add a weed-blocking landscape fabric—camouflaged by mulch—around the plant’s main stem.

How does using fish meal or kelp benefit a garden? —M. O., Hortonville, Wisconsin

Fish meal and kelp belong to the group of fertilizers and soil amendments—generally referred to as organic—that are composed of natural plant and animal materials. Fish meal is made up of ground-up fish parts that are a byproduct of the seafood processing industry. Although some people find its odor disagreeable, fish meal is a slow-release fertilizer that contains relatively balanced proportions of the three major plant nutrients: nitrogen, phosphorous, and potassium, as well as small amounts of several trace minerals.

Kelp meal—made of ground-up seaweed—is relatively low in nitrogen and phosphorous but contains many vitamins, minerals, and soil conditioners. Kelp meal decomposes quickly to improve soil structure, but because of its low nutrient content, it is often classified as a soil amendment rather than a fertilizer. Fish and kelp meal are available in dry and liquid forms; some products combine fish and kelp. Check the labels of individual products for application rates.

Walt Benecki, owner of Walt’s Organic Fertilizer Company in Seattle, Washington, says that using fish and kelp meal helps to improve soil fertility—a key to successful gardening. “Adding nutrient-rich organic fertilizer to the soil is like using a key to unlock those plentiful nutrients that are present in most soils but that are in forms that plants cannot use,” Benecki says.

Many garden centers carry kelp and fish fertilizers. One mail-order source is Peaceful Valley Farm Supply in Grass Valley, California. Order its free catalog by calling (888) 784-1722, or visit its Web site at www.groworganic.com. B