Asparagus - Both Ancient and Modern
Quick quiz: What is the spring vegetable that spans the ages — grown in ancient times and eaten by Julius Caesar yet showing promise for a future space colony, shown to be tough enough to tolerate Martian soil according to NASA? Need a few more clues? This workhorse is loaded with vitamin K and folate, and may help to reinforce the walls of blood vessels and relieve hangovers. Still wondering? It’s an easy-to-grow perennial that puts a smile of the face of many gardeners, yet makes them turn pale when they see the pricey bundles of it sold at grocery stores. Yes, you’ve guessed it — good old asparagus!
Asparagus is a perennial that, with proper maintenance, can remain productive for up to 30 years and, since it does require a bit of a workout to install, proper site selection is important—you don’t want to be disturbing and moving the bed a few years down the road.
Choose a location with good drainage and full sun (at least 6 hours) that has not been planted with asparagus previously (as fungal diseases may persist in soil). Have the soil tested—asparagus does not grow well in acid soils; if test results indicate low pH, amend the area with limestone according to test recommendations to raise soil pH to around 6.5-7.5. For info on getting a soil test from the UMass Oil and Plant Nutrient Testing Lab, go to soiltest.umass.edu.
Asparagus can be started from seed, but is easier to establish from one-year-old bareroot plants known as crowns (each crown appears as a short section of stem with attached roots and has been grown from seed). Buy from a reliable nursery supplier (conservation district plant sales can be an affordable option for purchasing crowns). Select cultivars such as ‘Jersey Supreme’, ‘Jersey Giant’, ‘Jersey Knight’, ‘Millenium’, or the purple cultivar ‘Purple Passion’, which are resistant to or tolerant of major asparagus diseases — rust and Fusarium crown and root rot.
Although asparagus can survive in barren soils from Mars, you’ll want to give your plants the best start by spreading and working in a several inches of organic matter — compost, leaf mold, or aged manure — as well as any general purpose (10-10-10) or equivalent natural fertilizer as recommended by the soil test.
Once soil amendments are worked in, stretch your back, because you’ll be digging a trench — approximately 12 inches wide by 6 to 8 inches deep for the new arrivals (dig slightly deeper in sandy soil, shallower in heavy soil). Place crowns in the bottom of the trench, spaced about 12 inches apart, with their roots spread out. Cover the plants with 2 inches of soil and water thoroughly. As the season progresses and shoots continue to grow upward, you’ll want to backfill the soil a few inches at a time (avoid covering asparagus foliage) until the trench is filled level with surrounding ground. A single trench of asparagus should be kept about 3 feet from other crops, and if you are planting more than a single trench, space trenches 4 feet about from one another to give growing asparagus roots plenty of room to spread.
During the first year, keep the asparagus bed deeply watered (8 to 12 inches deep) once a week; asparagus’s extensive root system makes it fairly drought tolerant after it’s established, so frequent watering in subsequent years is usually not necessary. Keep asparagus beds weeded to reduce competition for water and nutrients, and once the trench has been fully backfilled, use straw or shredded leaf mulch around plants as a long-term means of keeping weeds at bay.
Fertilize asparagus in early spring (before spears emerge) by working in a 1-inch layer of compost or aged manure, or apply 10-10-10 (or a natural fertilizer equivalent) according to label directions. Make a post-harvest (third growing season and beyond) feeding with a high-nitrogen fertilizer or several inches of aged manure to boost plant growth throughout the rest of the growing season and safeguard the following year’s crop.
If you’ve planted disease-tolerant cultivars, your main concern will be pest control. One culprit to keep an eye out for is common asparagus beetle, ¼ in length, and blue-black in color with 6 cream square-ish spots on its back. It feeds on the growing spears, and affected spears tend to turn brown and bend over at the tip. Monitor plants regularly: rub off any clusters of dark brown eggs you find attached to spears, and handpick larvae and adults to drop in a container of soapy water. You may also find adults of the spotted asparagus beetle, which is red-orange with 12 black spots. Their damage can be problematic, but they are not as destructive as the common asparagus beetle.
Once the harvest season is over (after about 6 weeks, when emerging spears are skinny), allow remaining spears to grow tall and produce their fernlike foliage. Cut down the stalks to ground level after they’ve been frost-killed, and remove them from the garden to prevent any lingering pests or disease-causing organisms from overwintering. This is also a good time to test soil pH and adjust with lime to asparagus’s preferred range if necessary.
As tempting as it may be, refrain from harvesting asparagus spears in the first and preferably second years. This will allow plants to build up a robust root system to support long-term production. However, if you’re finding it hard to wait, take note: research reported by Purdue University suggests that a couple of weeks of judicious harvesting in the second year can actually stimulate bud production and result in better crop yields in later years.
Beginning in the third growing season, harvest spears that are 6 to 8 inches long and thicker than a pencil every few days over a 2- to 3-week period. Subsequent years’ harvests can gradually increase up to a period of up to 6 weeks, as long as plants continue to produce adequately-sized spears.
No special equipment is needed to harvest asparagus—simply snap off spears just above ground level. Conveniently, asparagus tends to snap at a spear’s transition point from tender to tough. Asparagus is best eaten soon after harvest as it loses its sugar content quickly, but the spears will keep in a plastic bag in the refrigerator for up to a week while you harvest enough for a meal.
- Kujawski, Ron and Jennifer. Week-by-Week Vegetable Gardener’s Handbook. Storey Publishing, North Adams, MA.
- Lerner, B. Rosie. Purdue University Cooperative Extension Service Fact Sheet: Growing asparagus in the home garden. Available online at https://ag.purdue.edu/hla
- Rupp, Rebecca. How Carrots Won The Trojan War. Storey Publishing, North Adams, MA.
- Tufts University Health and Nutrition Newsletter. Nutritious asparagus can put a spring in your step. Available online at https://www.nutritionletter.tufts.edu
- University of Massachusetts Home Lawn & Garden Fact Sheets. Asparagus-growing tips. Available online at https://ag.umass.edu/resources/home-lawn-garden
Jeninifer Kujawski, Horticulturist