Asparagus spears are the straight young shoots of the plant, with scale-like tips. Wearing gloves is recommended for handling young shoots, as contact dermatitis is likely. In late summer, female plants produce red berries that are toxic to humans. Later in the season, the foliage matures into an airy, light-green fern which changes to a golden color in the fall. This perennial is typically planted from roots, or crowns, in early spring. 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. They look like a worn-out string mop, but they are very much alive. 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. 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 with it 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. Remove weeds when preparing the bed, and keep weeding while the asparagus plants are young. Asparagus roots form a tightly woven mat, which makes it challenging to remove weeds. Add mulch to the bed to control weeds, but avoid interplanting with other crops- 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
For a long-lived perennial like asparagus, it pays to take the time to improve your soil. 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. Give them a good start when you first plant them and you’ll have fewer problems in future years. 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, it 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. These nutrients will help your asparagus develop a good, strong root system. To keep the soil rich and help feed the asparagus plants, top dress the soil annually with compost. You can 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.
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
In most cases, harvesting your asparagus spears won’t begin until the third year after they are planted. They need that time to become established and build up their root systems. This is especially true in the first year of planting when the shoots aren’t large. 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. 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. 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. 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.
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 too 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. They’re most active in the afternoon. Handpick the beetles and drop them in a bucket of soapy water when there are only a few. Otherwise, diluted neem oil should keep them under control.
