I love looking at the delicate beauty and play of light filtering through fine-leaved asparagus stalks in summer, especially as a backdrop to bolder-leaved plants and flowers. Few gardeners cultivate asparagus for this purpose, and it’s an added bonus to its springtime bounty of weird-looking edible spears.
Asparagus holds an almost unique position in the vegetable garden by being the only green vegetable in temperate climates which is routinely cultivated as a perennial crop. There are a host of other minor perennial vegetables and herbs – for example Jerusalem artichoke (Helianthus tuberosus), sea kale (Crambe maritima) or Chinese artichoke (Stachys affinis) – but none have the wide appeal of springtime asparagus. Because it is a perennial, it requires its own unique space, one that can serve as a relatively permanent bed for 20-plus years. It is a plant that enjoys solitude, disliking any weed competition or companion plants.
One key to great asparagus yields is an extremely well-prepared site. The new bed should be weed free, especially of any perennials, so depending on your situation, you may need to prepare the bed up to a year in advance. Asparagus generally prefers full sun. Covering the area with cardboard, organic mulch or black plastic can be helpful in smothering weeds. Asparagus prefers a fertile, reasonably well-drained, loamy soil. In most situations, very generous additions of compost, leaf mold and/or rotted manure are required. Since asparagus is a “permanent” crop, the investment of time and money is worthwhile.
When planting, incorporate a granular organic fertilizer for its long-term benefit. Rock phosphate is a beneficial source of slow-release phosphorus. If you have dense, clay soil, additions of sand, fine gravel, granite dust or greensand may be helpful.
The bed is often dug as a trench to a depth of 18 inches, and then backfilled. While asparagus requires adequate moisture, a well-made bed situated in a clay envelope can retain too much moisture, thus reducing aeration if there is insufficient drainage away from the bed. Raising the bed can help in dense soil conditions. Building a raised box may be an easier solution than deep digging, especially in heavy soil. The bed’s productive life will likely outlast your wood frame, which will need replacement at some point.
In its native habitats, asparagus is found growing in moist places and seashores, and is tolerant of saline conditions. You may have noticed wild asparagus growing in less than ideal sites. While it can grow in a variety of terrains, if you want good yields, you should optimize your growing conditions. Some old-timers say that additions of salt to the asparagus bed will help kill weeds. Because asparagus is salt-tolerant while other plants are not, this works in principle. I don’t recommend it, however, because it can harm the soil.
The modern hybrid varieties of asparagus have formed an exclusive male-only club. Because the plants are all male, the energy of the plant does not go to making flowers, fruits or seeds, and yields are greater. Male plants also have a greater longevity than females. These varieties will perform better in a shallower soil situation than the old types, and thus require less than a foot of soil preparation. With older types of asparagus, a routine practice was to plant extra plants, and when it became evident which plants were females, rogue them out. Female plants tend to be less productive with a shorter life span.
Asparagus crowns (rhizomes) are planted in the spring. I recommend buying good size 1-year-old roots from a reputable supplier, not from the supermarket. Plant 12 to 18 inches apart, in rows 3 to 5 feet apart in a 6- to 8-inch-deep furrow or trench. Cover with a few inches of soil. As the shoots grow, gradually fill in the furrow. Closer row plantings may be made in a well-prepared bed as long as the plants are staggered. Roots need not be planted in rows. After planting, make sure the roots are well-watered, and cover the bed with light mulch like chopped straw. Roots should not get cultivated during the first year, or they could be damaged. Plants take about three years to reach maturity. You should refrain from picking the spears the first two years.
Asparagus is not hard to grow from seed, but add one more year to achieve yields. Typically, seeds are sown outdoors in a very well-prepared seed bed and transplanted to their permanent location in one or two years.
Varieties to try
Asparagus was planted in America sometime before 1672. Philadelphia seedsman Bernard McMahon’s broadside catalog of 1804 lists two varieties: Gravesend and Battersea. The modern thicker-stemmed asparagus was developed in the late 18th century. By the latter part of the 19th century, there were many American varieties, including Barr’s Mammoth, Conover’s Colossal, Columbian Mammoth White, Donald’s Elmira, Eclipse, Hub, Moore’s Cross-Bred, and Palmetto. Two basic colors of asparagus were common: green, which varied from medium to light green, and white. Truly purple asparagus is of modern origination derived from purple tinged heirloom varieties.
Older heirloom asparagus varieties are quite hard to find. Conover’s Colossal is available as seed from a few online sources. It was introduced in 1868 by J.M. Thorburn Company of New York, and developed by S.B. Conover. It has green spears tinged with purple, and produces thick stems more than an inch wide.
Similarly hard to find is a French variety Precoce D’Argentuil, Early Purple Argenteuil or some variation of that name listed by the French seedsman Vilmorin-Andrieux in 1885. It has rose-purple-tipped spears with white stalks, excellent taste, and yields from seed relatively quickly. This type was often blanched to produce white spears.
Mary Washington is one of the standard old-timers that was developed in a breeding program specifically for rust resistance in Concord, Massachusetts, around 1910, along with its sister variety Martha Washington. Mary produces good early yields of long green spears of excellent quality. Its tall non-branching habit produces extra-long spears. Through the years, a variety of strains have been produced with slight differences. Mary is available as seed, and probably the only heirloom variety available as crowns.
Purple Passion is a modern open-pollinated variety with burgundy spears and a light green interior. One of its parents was an heirloom discovered in Switzerland. It is sweet and tender with a nutty flavor, and is good for fresh, uncooked eating. Sweet Purple is a similar hybrid variety released around 1997. It is an attractive burgundy-purple color, yielding large tender spears, with noticeable sweet flavor that also makes excellent raw eating.
Another modern hybrid is Jersey Knight, which has become a standard variety for gardeners, especially in the North. It was developed by Rutgers University in New Jersey as part of the Jersey series, yielding mostly male plants. It has good resistance to rust, fusarium and crown rot, as well as medium green, large spears with good yields and taste. It grows fairly well in heavy soils. Jersey Giant and Jersey Supreme are similar – both are earlier bearing, and Jersey Giant has purple bracts.
While lacking an appealing name, Viking KB3 is an open-pollinated variety that is considered very hardy yet will perform well in hot, dry areas. It has good yields and does produce female plants. Another performer in warm climates with a lackluster name is UC 157, developed at the University of California at Riverside. It has good yields, green spears, and is disease resistant. This variety is not suitable for cold climates, being hardy only to Zone 6.
One strategy for the kitchen garden is to plant a bed of heirloom asparagus and a bed of hybrid. That way you get the best of both worlds and can try your hand at seed-raised plants. And if you raise enough heirloom plants, you can even spread some history to your neighbors.
Lawrence Davis-Hollander is an ethnobotanist, plantsman and gardener, former director and founder of the Eastern Native Seed Conservancy, and currently a contributor to Dandelion Gardening Arts in Norfolk, Connecticut.