Asparagus is a perennial vegetable native to Western Europe on limestone soils. Asparagus is a member of the lily family and the Asparagus family includes many species prized for their ornamental values. “Asparagus asparagoides (medeoloides), commonly known as Smilax, has long twining shoots furnished with small, broad, shiny leaves; it was formally in great demand for floral decorations, but is less used today.” Asparagus verticillatus grows about 10 feet high and bears an abundance of red berries. It is an excellent plant for draping a pillar in the greenhouse. Asparagus fern, Asparagus plumosus and its varieties are tender perennial plants with underground fleshy roots, erect or climbing stems, and tiny spiny branches bearing inconspicuous flowers which are followed by round, reddish berries containing small black seeds. They are grown out doors in frostless or near frostless regions, elsewhere in greenhouses and as house plants. They prefer rather shady moist conditions, and should be grown in a compost of loam and leaf mold with a scattering of sand. The minimum winter temperature of the greenhouse should be 50 degrees. The ornamental kinds of Asparagus are grown for the value of their graceful leafy shoots, which are admirable for cutting for decorative purposes. Most of the greenhouse kinds are natives of South Africa. Although they are moisture loving plants and require an abundance of water during the summer, they must be rested during the winter by allowing the soil to become almost dry before it is watered: they are liable to lose their leaves in winter if overwatered. Well rooted plants derive great benefit from biweekly waterings with dilute fertilizer during the summer.”
The common edible asparagus will last at least 20 years in the garden. It’s crucial to properly prepare the site prior to planting so that there will be a good depth of rich, fertile, well-drained soil. Asparagus prefers rich sandy well drained loam soils. In the case of clay soils the ground should be excavated to a depth of 2 feet, and drainage should be encouraged by putting in stone, broken brick, or modern perforated plastic tile along with the addition of organic matter in the subsoil. Spade manure, leaf mold, rotted leaves or peat into the bottom of the trench. The soil that has been dug from the trench should now be prepared by spading organic matter into it along with at least 4 ounces or more of bone meal per square yard. In Western Washington and Oregon, with the regions acid soils, we also recommend adding lime at a rate of about one pound of dolomite lime into each 10 feet of trench. Bone meal works like lime and also contains phosphorus. If lime is used rather than bone meal, it is important to add phosphorus. Use a 0-20-0, or even a 0-40-0, spreading in liberally in the bottom of the trench or furrow.
Before proceeding, it is important to point out that the organic clay asparagus bed should be prepared in the Fall of the year. The asparagus roots should be planted in the spring (late February through early April). This allows the organic matter to compost thoroughly prior to planting the asparagus roots, and this foresight and patience on the part of the gardener can spell the difference between success and failure. Asparagus roots are soft and starchy, rather than woody, and can easily compost if planted with rotting manure, etc.
Spring planting is recommended for asparagus roots. In clay soils that have been properly prepared last Fall, plant the crowns at soil level or just 1 to 2 inches below and cover with 2″ of soil. In the fall, cover with 2 more inches of soil. Asparagus crowns migrate to the surface of the soil over time because the new crown grows on top of last year’s crown every year. Asparagus beds should be maintained so 3 to 5 inches of soil covers the crowns. Crowns that are cultured too shallow yield spindly spears. Crowns that are cultured too deep tend to grow to the surface more rapidly, and yield of the early crops are adversely affected. For maximum yield it is important to properly orient the crowns when planting with the crown on top and the roots or “legs” spread in a downward direction. This is most easily achieved by forming a ridge of soil placed in the center of the trench, or individual pyramids of soil placed in the center of the trench so the crowns can be properly “perched” on the ridge or pyramids prior to covering with soil. Never allow two plants to touch in the planting trench. A spacing of 15 to 18 inches is about right.
The above planting instructions are especially recommended for growers in Western Oregon and Washington State, where clay, acid soils are quite common. If one is blessed with a sandy loam–well drained soil, then only lime, phosphorus and bone meal amendments are crucial to success. The addition of organic matter is always helpful, but not mandatory. Again, if incorporating organic matter, be sure and do so far enough ahead of time so composting does not occur at the time of planting.
On well drained sandy–loam soils far less bed preparation is mandatory. Trenches 12 inches wide, 8 inches deep and 4 to 6 feet apart work nicely. We recommend planting and maintaining the same depth in the discussion of clay soils.
Once established, asparagus is easy to care for. Asparagus is extremely deep rooted and therefore water and nutrients are not as critical as is the case with a lot of crops. At our nursery we have grown test plots of asparagus with no irrigation or fertilizing several years in a row. Our theory has been the asparagus roots lay deep enough to pick up moisture and nutrients on their own. We do water and fertilize nearby crops and in the home garden this is normally the case as well. Oregon State University Extension Service wrote a flier based on information gleaned from “Growing Asparagus in the Garden” by Harwood Hall, Susan Wadea, Ronald Voss, a University of Cal. publication, leaflet 2754 and “Commercial Growing of Asparagus” U.S. Dept. of Agriculture Farmer’s Bulletin No. 2232. The OSU Ext. flier writes “Fertilize annually when harvest has been completed and the plants begin to fern out. Apply manure and 8 to 10 pounds of a complete fertilizer (5-10-10 or 1-10-5) per 100 feet of row. Most irrigation should be done during the “fern season,” not the harvest season. Control weeds by hoeing; avoid wounding the plant or the soon to emerge spears.”
Insects: “The asparagus beetle and the spotted asparagus beetle can cause widespread damage. The adult asparagus beetle is 1/4 inch long, metallic blueblack with orange to yellow markings. It feeds on spears. The adult and it’s gray larvae feed on the berries. The spotted asparagus beetle is brick red with black spots. It feeds on both spears and ferns. It’s larvae feed on the berries.” In Western Oregon and Washington the 12 spot bean beetle also feeds on the fern during the larval stage. The bean beetle looks much like a ladybug beetle, only the bean beetle is yellow with black spots. Damage often begins in May. The Pacific Northwest Insect Control Handbook (1998) notes under the section on Home Garden Vegetable, Small Fruit, Tree Fruit and Nut Pest that carbonyl (Sevin)EC and malathion EC are cleared for use on the Asparagus beetles. Insecticide soaps and other remedies may be found in the full service garden center. One should check with your local garden center and carefully follow all directions and related information on the container, prior to using any insecticide or other plant “medicine.”
Don’t harvest spears the first year. The second season you can harvest for two or three weeks or until the spears develop ferny stalks. This practice encourages the roots to store food for the next year’s growth. In the fall when the top (fern) growth browns, cut off all fern growth at the ground level and dispose of it. Harvesting the 3rd year and there after can last from 8 to 12 weeks. Commercial growers cut asparagus 1 to 2 inches below ground level and at least 2 inches above the crown. A specially manufactured asparagus knife is helpful in cutting properly. This knife resembles a large “dandelion digger,” which also serve as a suitable harvesting tool. For our own use we don’t bother cutting below the ground level. We just snap the spear off near the ground. If the spear bends, rather that snaps, it will be tough and can best be used by peeling the outer layer or epidermis off the tough portion of the spear. Europeans use special asparagus racks to cook peeled spears, so they don’t fall apart in boiling water. We prefer to just snap off spears knowing if they “snap” they will be tender and require no peeling. We like to pick a large batch of spears and steam them in a steamer cooker. After 2 to 3 minutes the asparagus is “blanched” and a portion can be taken out of the steamer and frozen for later use. Asparagus is normally fully cooked in 12 to 18 minutes in a steamer. Picking asparagus in the late part of the day yields more tender spears than picking in the morning. Asparagus grows fast during the warm hours of the day, it tends to be really tender in the evening!
In regard to nutritional value, USDA leaflet 2754 notes “A 1/2 cup serving of asparagus spears contains only about 18 calories, and about 1/4 of the adult daily recommendation (RDA) for vitamin C. Asparagus is also a significant source of vitamin A, iron and other essential trace nutrients. White asparagus (which has been bleached by mounding dirt around the growing spear) contains only about 1/10 of the vitamin A value of the green type.” As an aside, another way to produce white asparagus is to cut a 55 gallon drum in half lengthwise, or use a plastic drum cut in half, and lay this over the top of the asparagus bed so it creates a “shed” or “garage” effect. This keeps light from striking the spears as they emerge and one only has to lift the end of the drum to discover the white spears beneath it.
If you have read this far, you should be equipped to successfully grow asparagus in your garden…ENJOY