Asparagus is one of the first vegetables ready to harvest in the spring and also one of the few perennial vegetables grown in the garden. Since it will be in the same place for years, it's important to find a spot with all the growing conditions it needs. Asparagus plants are slow to mature, taking three to five years to really fill in, but it's worth the wait. Once they start producing well, you will be harvesting asparagus spears for more than a month every spring.
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.
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|Botanical Name||Asparagus officinalis|
|Plant Type||Perennial, vegetable|
|Mature Size||4 ft. tall, 2 ft. wide|
|Sun Exposure||Full sun|
|Soil Type||Sandy, loamy|
|Soil pH||Neutral, acidic|
|Bloom Time||Summer, fall|
|Flower Color||Yellow, green|
|Hardiness Zones||3-10 (USDA)|
|Native Area||Europe, Africa|
|Toxicity||Berries toxic to humans|
How to Plant Asparagus
Your asparagus spears may not be big enough to harvest for up to three years, but you want to prepare the bed for the best results. Because asparagus is a perennial, you'll need to designate a place in the vegetable garden or, even better, build a separate bed. 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 there are both male and female plants, meaning they will produce seeds and will self-sow. Newer hybrid varieties produce only male plants that don't have seeds, so they need a little less space because they'll spread only through the growth of the existing crown.
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 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.
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.
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.
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.
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.
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.
Why does it take three years to grow asparagus?
That's the time that it takes a young seedling to grow into a strong plant that is harvested for four weeks or longer every year. By starting with healthy, vigorous one- to two-year-old crowns from a garden center or seed catalog, you increase your chances of being able to harvest after the three-year wait period.
Does asparagus keep growing after you cut it?
The same stalk won't regrow after you cut it but in an established asparagus patch, you will have multiple stalks growing and popping out of the ground at different times. The asparagus stalks that you have cut will regrow the next year because asparagus is a perennial.
How much asparagus do you get from one plant?
One crown produces about half a pound of spears. If you want to harvest 10 pounds per season, you'll need a row of 20 plants, spaced one foot apart.
Can I grow asparagus in pots?
Theoretically, asparagus can be grown in outdoor containers, but the process is not very practical for several reasons. Asparagus roots must develop for two or three years before they produce stalks that can be harvested, and if you do manage to grow it to maturity in pots, the plants will exhaust themselves within a couple of years. Thus, it's generally not worth the effort to try container culture.
Can I grow asparagus indoors?
When asparagus is grown indoors, it is usually by commercial growers who use special hydroponic equipment, which is prohibitively expensive and difficult for DIYers to maintain. Asparagus requires cold winters to reset the roots, thus it is not practical for indoor growing. However, seeds are sometimes started indoors, then planted outdoors in the garden in the spring.
Asparagus officinalis. NC State Extension.
Asparagus Planting Time. University of Missouri Integrated Pest Management.
Camire comments on white asparagus for Tribune News Service. The University of Maine.
Frequently Asked Questions for Asparagus. The University of Maine Cooperative Extension.
Djalali Farahani-Kofoet, Roxana, et al. Species-Specific Impact of Fusarium Infection on the Root and Shoot Characteristics of Asparagus. Pathogens, vol. 9, no. 6, 2020, p. 509. doi:10.3390/pathogens9060509
Morrison, William R., and Zsofia Szendrei. The Common Asparagus Beetle and Spotted Asparagus Beetle (Coleoptera: Chrysomelidae): Identification, Ecology, and Management. Journal of Integrated Pest Management, vol. 5, no. 3, 2014, pp. 1–6. doi:10.1603/IPM14004