How to Grow Asparagus in the Midwest

Many gardeners have tried tomatoes, zucchini, and cucumber but given little thought to perennial vegetables. If you are ready to take the plunge and are willing to wait more than one season for a crop, growing asparagus is a fun project.

Asparagus plants provide years of an expensive crop at a relatively low up-front cost. At Park Seed, a mail-order nursery, a package of 20 plants, plenty for a family plus some for freezing, costs about $15. Although it may take 3 years to recoup the intial investment, asparagus costs $3-$5 per pound at the grocery store, and plants produce for 15-20 years. This means that gardeners who grow asparagus can get a return many times the cost of the plants.

Like homegrown tomatoes, homegrown asparagus tastes better. Freshly picked, homegrown spears are tender and more flavorful than those from the grocery store.

Asparagus is a long-lived perennial. Spears are harvested in the spring, for about a month starting in April or May. The mature foliage on the plant is tall and ferny. The plants will eventually become large, about 3-4 feet tall by mid-summer.

Asparagus requires rich, well-drained soil. Because it is a perennial, soil cannot be tilled to remove weeds once the soil is planted. According to the Ohio State University Cooperative Extension office, the plants prefer a soil pH of 6.4 to 7.5, and not lower than 6.0. The OSU Extension Office advises that the site should not be one that floods; poor drainage may lead to root rot. They suggest the West or North side of the garden, to keep the plants from shading other vegetables.

When establishing an asparagus bed, begin by tilling the soil deeply, to at least 6 inches. Add plenty of well-rotted manure or mushroom compost, and replenish this annually. The manure or compost provides nutrients and organic matter required for the plants to thrive. Purdue University experts recommend bone meal, blood meal, and wood ash as an alternative to compost, manure, or chemical fertilizers.

Although asparagus can be grown from seed, the plants are inexpensive enough that it is worth spending the money to get one-year-old crowns from a grower. Asparagus crowns are available at home centers in early spring, but ordering asparagus crowns online offers homeowners more choices.

All-male hybrid asparagus varieties are generally more productive. An added problem with female plants is that they produce seedlings, which can lead to weed problems in the garden. The most common named all-male varieties, Jersey Giant, Jersey Prince, and Jersey Knight, produce much higher yields than older, mixed-gender varieties, such as Mary Washington or Martha Washington. Some varieties, such as Purple Passion, produce purple spears that turn green when cooked.

The University of Illinois Extension Office recommends planting asparagus as soon as the soil can be worked in the spring. Ohio State University's advice differs. They suggest waiting until the soil has warmed to 50 degrees F, because this reduces the risk of Fusarium crown rot.

To plant the crowns in rows, dig a furrow about 5 or 6 inches deep. Place the crowns in the furrow. Some fertilizer placed in the furrow with the crowns may, according to the OSU Extension Office, be beneficial. Space crowns 1 ½ feet apart, and space rows 5 feet apart from center to center. If rows are not used, as in non-traditional gardening styles like lasagna gardening, place the spears 1 ½ to 2 feet apart. After planting, refill the furrow to its original soil height and cover with a thick layer of mulch.

Asparagus should not be harvested the first year it is planted. The first year, a few thin spears will emerge, and plants will not withstand the stress of a harvest.

Each plant produces spears from buds on the crown. As the spears grow longer, they open and form small branches that look like ferns. These produce the food for the plant, which is stored in the crown to produce the next years' spears. The stems or spear will become woody during the summer.

Asparagus tolerates drought well and requires little or no watering, because the roots of mature plants seek moisture deep in the soil. The first year after planting, however, it may be necessary to water.

Common pests and diseases include the asparagus beetle, which chews on the fern and causes the stem to turn brown. The beetles will reduce yields the following year. Purdue University offers advice on insect management.

The OSU Cooperative Extension Office recommends leaving dead ferns intact over winter to catch snow for additional soil moisture and keep the winter soil temperatures warmer. Waiting until April to cut down the dead stalks also reduces the risk of frost damage by preventing spears from emerging too early in the spring. Dead stalks are sharp, and gardening gloves may be helpful.

In the second year after planting, harvest lightly, if at all. A light harvest means cutting a few spears over a three-week period. According to Ohio State University, research has shown that waiting until the third year is not necessary, and that harvesting the second year stimulates crown bud production, which will increase yields in future years. The conventional advice, however, is to wait until the third year to harvest.

Asparagus spears emerge when the soil temperature reaches 50 degrees F. Early in the season, 7 to 9 inch spears are harvested every few days. As the air warms, spears must be harvested more frequently but will be shorter. Late in the season, the tips will "fern out" and be of poor quality. Ohio State University recommends discontinuing the harvest when the diameter of three-quarters of the spears is less than 3/8 inch.

To harvest, snap 7- to 9-inch spears with tight tips. Cutting asparagus below the soil with a knife may injure other buds on the crown and decrease yields. Additional spears will grow from other buds on the crown.

When the harvest is finished, Ohio State University recommends snapping all the spears off at ground level and applying 1/2 lb. of ammonium nitrate fertilizer per 50 feet of row. An organic fertilizer such as compost could also be used. New spears will then emerge, fern out, and provide a canopy to cover the space between the rows.