How to Plant, Grow, and Harvest Asparagus

How to Plant Asparagus

When to Plant

Plants can be started from seed about four weeks before the last expected frost. However, seeds will add several years to your wait. Most people find it easier to grow asparagus from crowns, which are widely available in the spring. Unlike many plants, the roots of asparagus crowns can withstand some air exposure, and you will usually find them sold as bare roots. They should look firm and fresh, not withered or mushy.

Selecting a Planting Site

When considering how to plant asparagus in your yard, remember you’re in it for the long haul, even though you may not see a harvest for three years. Because asparagus is a perennial, you’ll need to designate a place in the vegetable garden or, even better, build a separate bed.

Spacing, Depth, and Support

Asparagus needs space, so plant the crowns 12 to 18 inches apart. They won’t spread out much in the first couple of years, but once established, they will quickly fill in. Heirloom varieties need extra space, as they produce seeds and will self-sow. Newer hybrid varieties produce only male plants that don’t have seeds, and will spread only through the growth of the existing crown.

The most common way to plant asparagus crowns is in a trench. In the spring, dig a trench about 12 inches deep and 12 inches wide. Combine your compost, fertilizer, or other organic matter, and create mounds about 18 inches apart. Set the crown on top of the mound, spreading the roots down the sides. The top of the crown should be about 6 inches below the soil line. Cover the crown with soil, and water well. As shoots appear, add more soil to fill the trench until it’s flush with the soil line.

Asparagus roots form a tightly woven mat, which makes it challenging to remove weeds. Make sure you control weeds before planting and while the plants are young, then add mulch to the bed to control weeds. Avoid interplanting with other crops because asparagus dislike competition for nutrients.

Asparagus Care

Light

Asparagus plants grow best in full sun. Without enough daily sunlight, you will wind up with thin spears and weak plants that are prone to problems.

Soil

Because it is a long-lived perennial, soil quality is key in how to grow asparagus successfully. Work in plenty of organic matter and make sure the soil pH is in the neutral 6.5 to 7.0 range. Also, get rid of any weeds and large stones in the area. The soil must drain well so the plants are never sitting in water.

Water

Asparagus needs regular watering, especially while young; give it 1 to 2 inches of water per week during its first two growing seasons; give older plants about 1 inch per week. Consider adding drip irrigation or a soaker hose to the asparagus bed.

Temperature and Humidity

During the growing season, asparagus prefers a temperature of 70 to 85 degrees Fahrenheit during the day and 60 to 70 degrees at night. In the spring, asparagus will begin to grow shoots when the soil temperature reaches 40 degrees. Any frost after the shoots start growing will cause damage. You may see slow growth with temperatures above 85 or below 55 degrees.

Fertilizer

When preparing your asparagus bed, add compost and an all-purpose organic fertilizer to the trench, as well as rock phosphate, a natural mineral powder that promotes root growth. To keep the soil rich and help feed the asparagus plants, top dress the soil annually with compost. Do this in early spring before the shoots appear, or in the fall after the fronds have died back and been cut to the ground. Asparagus is a heavy feeder, and you should also give it a dose of fertilizer in mid spring when it is actively growing, following product label instructions.

Types of Asparagus

The newer cultivars are bred to be all male, which means they will put all their energy into growing the plant, not setting seed. Some popular choices include:

• ‘Mary Washington’: The most commonly found variety; bred for rust-resistance
• ‘Jersey Giant’: Yields early and is resistant to rust and fusarium wilt
• ‘Brock Imperial’: Prized for its high yield
• ‘Princeville’: Does well in warmer climates
• ‘Purple Passion’: A sweet purple variety

Green vs. White Asparagus

White asparagus is the same plant as green asparagus, but it turns white through a process called blanching, which deprives the plant of light so it does not photosynthesize. This is accomplished by covering the growing spears with either soil or plastic tunnels. The final product is smooth, white, and virtually fiber-free, provided the harvested spears are immediately chilled to prevent the fiber from forming.

Harvesting Asparagus

In most cases, harvesting your asparagus spears won’t begin until the third year after planting. Here’s a timeline of what to expect as you navigate how to grow asparagus:

• First year: The plants need this time to become established and build up their root systems, especially in the first year of planting when the shoots aren’t large.
• Second year: Some gardeners harvest spears if they are the thickness of a pencil or more during the second year. For healthy, well-established asparagus plants, patience is key.
• Third year: By the third year, you should be able to harvest for about two weeks. Then let the new spears grow undisturbed after that initial harvest. Fronds will unfurl from the spears, creating the pretty, airy foliage that feeds the plant.
• Fourth year: In the fourth year, begin harvesting spears that are 5 to 7 inches long before the tip becomes loose (diameter doesn’t matter). You can either snap off the spears or cut them with a knife, just above the soil line. If you use a knife, be careful you don’t also slice the later shoots that are still underground and haven’t yet poked through.
• Fifth year and beyond: Harvest for about four to six weeks in the fifth year. In subsequent years, the shoots will continue emerging from the soil throughout the spring. After you’ve been harvesting for more than a month and the weather starts to warm, the shoots will begin to get spindly. At this point, allow the plants to grow into their mature ferny foliage, which will feed the roots for next year’s crop. Asparagus plants can continue producing for 20 to 30 years and can be divided or transplanted if they become overcrowded or could benefit from a move.

How to Grow Asparagus From Seed

Typically, gardeners grow asparagus from bare root crowns, which help you get ahead of the two to three years it takes to get asparagus from seed to harvest. However, if you do want to grow asparagus from seed, it’s best to start them indoors in late winter under a heat lamp.

Soak the seeds overnight before planting them half an inch deep in a seed starting tray. The soil will need to be 70 to 85 degrees Fahrenheit for germination. It takes between two to eight weeks for the seeds to sprout, and you can transplant them after the last frost. Then it’s a matter of patience as you wait for the harvest a few years down the road.

Overwintering

Asparagus plants need to be cut to the ground each year before the new growth starts. The timing is up to you. You can remove the stalks in the fall or winter after the leaves have turned yellow and died back naturally. The advantage of early removal is that it prevents pests, such as asparagus beetles, from overwintering in the stalks. Leaving the stalks standing through the winter, on the other hand, has the advantage that the plant debris can hold snow, which protects the asparagus crowns in freezing temperatures. In any event, the dead stalks must be removed in the spring before the new growth starts.

Common Pests & Plant Diseases

Asparagus does not have many problems in the garden. Fusarium wilt can be a problem with older varieties, but you can avoid it by planting resistant hybrid varieties. The biggest pest is the asparagus beetle. Keep watch for them as the spears emerge in spring, especially during their active time in the afternoon. If there are only a few beetles present, handpick the beetles and drop them in a bucket of soapy water. Otherwise, diluted neem oil should keep them under control.