Asparagus

Recommended Varieties

• 500W
  

  Asparagus takes several years to mature. Asparagus shoots (spears) should not be harvested the first season after crowns are set. Source: USDA
• Mary Washington
• UC 72
• UC 157

Growing Tips

Start asparagus from seed or 1 to 2 year-old crowns. (The crowns are rhizomes—fleshy stems that store food for future plant growth—with roots attached to their undersurface and the buds of emerging spears sticking up.) For best results, buy crowns from a respectable nursery. Starting plants from seed requires an extra year before harvest. Seeds may be started in peat pots; they are slow to germinate, so be patient. Seedlings may be transplanted in the fall. Crowns are usually set out in winter or early spring.

Choose a site with good drainage and full sun. The 3-foot-tall ferns of asparagus may shade other plants, so plan accordingly. Prepare the bed as early as possible and enrich it with additions of manure, compost, bonemeal or blood meal, leaf mold, wood ashes, or a combination of several of these.

In heavy soil, double digging is recommended. To double-dig, remove the top 1 foot of soil from the planting area. Then, with a spading fork or spade, break up the subsoil by pushing the tool into the next 10 to 12 inches of soil and rocking it back and forth. Do this every 6 inches or so. Double digging is ideal for the trench method of planting asparagus. The extra work of breaking up the subsoil will be well worth the effort, especially in heavy soil. The trench should be dug 12 to 18 inches wide, with 4 to 5 feet between trenches.

The same method may be used in wide-bed plantings, with plants staggered in three rows. Mix the topsoil that has been removed with organic matter (ideally, well-rotted manure) and spread about 2 inches of the mixture in the bottom of the trench or bed. Set the plants 12 inches apart, mounding the soil slightly under each plant so that the crown is slightly above the roots.

Crowns should be a grayish-brown color, plump, and healthy-looking. Remove any rotten roots before planting. Spread the roots over the mound of soil and cover the crown with 2 to 3 inches of soil. Firm well. As the plants grow, continue to pull the soil over the crowns (about 2 inches every 2 weeks) until the trench is filled. Water if rainfall is inadequate. 

Asparagus takes several years to mature. Asparagus shoots (spears) should not be harvested the first season after crowns are set. After spears shoot up, let them leaf out so that the foliage can nourish the growing roots and rhizome for future production.

Harvest lightly for 3 to 4 weeks the second year. The fleshy root system still needs to develop and store food reserves to support perennial growth in future seasons. Plants harvested too heavily and too soon often become weak and spindly, and the crowns may never recover. Add an extra year to the above schedule for asparagus started from seed; that is, do not harvest at all the first two seasons, and harvest lightly the third. When the asparagus plants are in their fourth season, they may be harvested for 6 to 10 weeks per year.

Weed the bed each spring before the first shoots come up to avoid accidentally breaking off spears. During production, it is best to pull rather than hoe weeds, if possible.

Harvesting

Harvest spears daily during the harvest period; use the asparagus or refrigerate it immediately in a plastic bag. The 6 to 8-inch spears are best and should be snapped or cut off just below the soil surface. If the asparagus is allowed to get much taller, the bases of the spears will be tough. Cutting too deeply can injure the crown buds that produce the next spears. Blanched asparagus is a gourmet item; to blanch (whiten) the spears, mound soil around them or otherwise exclude light from them so that chlorophyll is not formed in the stalks.

When the harvest is over, allow the spears to grow and leaf out. Asparagus has attractive, tall fern-like foliage that makes a nice garden border. Some gardeners prefer to support the growing foliage with stakes and strings to keep it tidy. In high-wind areas, plant the rows parallel to the prevailing winds so that plants can support each other.

There are several ways to extend the harvest period of your asparagus planting. One method is to plant at different depths: 4 to 6 inches, 6 to 8 inches, and 8 to 10 inches. The shallow plantings will come up first and can be harvested while the deeper plantings are just forming. This method results in a slightly longer harvest, but it may also cause some plants to be less vigorous than others.

A second technique for extending asparagus harvest has been the subject of university research and is highly recommended for home gardeners who have plenty of space. Plant double the amount of asparagus needed for your household. Harvest half of the plants as you normally would in early spring; then allow the foliage to grow for the rest of the season. During the early-harvest period, allow the ferns to grow in the other half of the asparagus planting. Then, cut the ferns in this second half in July or August. This causes the crowns to send up new spears, which can be harvested until late in the season.

If rainfall is short in summer, it helps to water the bed for good spear production. A light mulch helps keep the soil surface from becoming too hard for the shoots to break through easily. If using this method, harvest the spring bed only in spring and the fall bed only in fall. Otherwise, you risk weakening the crowns.

In all asparagus plantings, cut the foliage down to 2-inch stubs after freezing weather or when the foliage yellows. A 4 to 6-inch mulch of compost, manure, leaves, or other material added at this time will help control weeds and add organic matter and nutrients.