Growing Guide For Asparagus: Plant Care Tips

Fresh-grown asparagus is one of the most delicious harbingers of spring. This perennial vegetable overwinters in a dormant state, then sends up fat, tasty spears just when we need something light and green on our plates. Growing a patch of your own asparagus provides the freshest taste well before other crops are ready to harvest.

How to Plant Asparagus

Asparagus is a perennial that can live up to 15 years. It will require some patience and a long-term vision on your part. Prepare the bed in advance. When crowns are planted, they will need irrigation and weeding for another year before you harvest the first tasty spears.

Growing From Seed

It takes three years to grow and harvest asparagus from seed, but since you have to prepare the bed a year ahead of planting, start your seeds indoors at the same time. In February, soak the asparagus seeds overnight, then plant each seed ½ inch deep in a 4-inch pot. Keep them under grow lights at 75-80 degrees F, and don't let the soil dry out. They will take about 3-8 weeks to germinate. Transplant the seedlings when all danger of frost has passed. You can sow seeds directly in their plot, but the necessary weeding and the unpredictable weather conditions may give you trouble.

Growing From Dormant Crowns

According to the University of Minnesota Extension, growers should order or purchase their crowns in advance, timing the bed preparation and planting so that crowns do not dry out. Crowns must stay refrigerated ahead of planting.

When planting, add necessary amendments and till them in, then dig a furrow about a foot wide and 6-12 inches deep, a bit less for clay soil, a bit more for sandy soil, and leave the displaced soil next to the furrow. You can make the bottom of the furrow W-shaped (raised ridge down the center) so the crown is raised above any extra water. Each furrow should be about 4 feet from the next, as the plants will spread out over time, and you will still need a walkway. One recommended irrigation method is sub-surface drip tape, so if you will use this, dig the furrow a couple of inches deeper, then cover the tape with soil before planting the crowns.

The University of Minnesota Extension recommends laying them "head-to-toe", with the bud end just touching the roots of the next crown, roughly one foot from bud to bud. Cover with 3 inches of soil. When the buds come up, add the rest of the soil, a little at a time, around the spears as they grow.

Raised Beds and Containers

Asparagus can be grown in enclosed raised beds and large containers to avoid competitive weeds, but the space must be large enough for the plant to grow outward from the crown, one crown per 5-gallon container, for example. Follow the depth and spacing guidelines for planting in a field, and mix some compost into the soil each year to refresh the nutrients.

Asparagus Plant Care

Settle in for a long-term relationship with your asparagus bed. While it takes some regular weeding and feeding to grow successfully, your efforts will pay off. If you have chickens or geese, they can do the weeding for you.

Light

Asparagus thrives in sun to partial shade, depending on the particular climate and latitude. After growers discovered sun stress inhibited growth, a study was conducted and ultimately found that some varieties such as Walker Deluxe or Grande produce significantly more spears when under a 30% shade covering. Other types weren’t affected. However, if you live where the sun is less intense—Minnesota, for example, rather than central California—then full sun will be fine.

Soil and Nutrients

Since your asparagus will occupy a garden space for many years, it's best to prepare your asparagus bed a year ahead of planting, getting good tilth and organic matter, adding nutrients, and eradicating weeds. Once the plants are growing, these things will be harder to fix.

Test the soil to find out if potassium, nitrogen, and phosphorous are in balance and that the soil pH is between 6.5 and 7, then add any needed amendments. Work compost and even fresh manure into the soil well in advance of planting, though fresh manure should not be used closer to planting time. A cover crop such as ryegrass or white clover should be grown and turned in or managed as a living mulch.

The Pennsylvania State University Extension recommends fertilizing young plants in spring, before spears appear, spreading the fertilizer at an N-P-K (nitrogen-phosphorous-potassium) rate of 50-100-150 pounds per acre. Once plants are more than 4 years old, fertilizer should be added after harvest, in order to encourage ferns to grow.

Water

If your plot is very flat and your soil isn’t too sandy, you can apply furrow irrigation, filling shallow troughs that run parallel to your asparagus rows. Otherwise, lay in heavy-duty flat drip tape 3-6 inches below the crowns. 

Subsurface drip irrigation uses 10-20% less water than sprinklers, can be used to distribute liquid fertilizers, and doesn't interfere with harvest (or weeding), and it eliminates the loss of water from the soil surface. Water two to three times per week according to your soil type, weather, and evapotranspiration rate. Do not over-water, or the crowns will rot.

Common Pests and Diseases

Asparagus beetles are bright orange pests that over-winter in the dried fern-like stems. They lay their oval eggs perpendicular to fern stems and then as larva feed on the asparagus spears, causing them to curl. Remove dead ferns before winter and burn them if possible.

Clearing away dead ferns can also reduce damage from aphids and diseases. Harvest all the spears, so they don't harbor diseases and monitor during the off-season for pests or diseases on the ferns.

Asparagus Varieties

Find a variety of asparagus that has a proven success record for your region. Your local nursery will stock what works for your climate, but if you buy online, do your research.

• Standard green varieties include Martha Washington and Mary Washington. There are also all-male hybrids, such as Jersey Giant, which produce more hefty spears.
• Purple asparagus, such as Purple Passion, was established in the Albenga region of Italy and originally called "Violetto d’Albenga." The color may disappear if you boil it, but the anthocyanins, powerful phytonutrients, attached to the color will remain.
• White asparagus, a favorite item in Europe, is a bit sweeter and very tender, but it isn’t a variety so much as it is a method of hilling dirt up around the spears to block the sun and stifle chlorophyll production.

How to Harvest, Store, and Preserve Asparagus

Do not harvest asparagus the first year it produces spears. These need to grow into "ferns", so the plant has enough vegetative growth to store the energy needed to over-winter and expand. In the second or even the third year, asparagus produces mature spears during a 6-8 week window. Using a sharp knife, cut the stalk of the asparagus at the soil surface—no lower, or the crown may be damaged. Cool immediately, plunging the asparagus into cold water, then wrap it in a plastic bag.

Fresh asparagus can be stored like a cut flower, standing upright in the water. Preserve raw or blanched asparagus using a pressure canner and following instructions from food safety experts such as the National Center for Home Food Preservation.