Asparagus is one of the first vegetables that is 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 spot for years, it's important to find a spot where it will have all the growing conditions it needs. Asparagus plants are slow to mature, taking three to five years to really fill in and mature, but it's worth the wait. Once they start hitting their stride, you will be harvesting asparagus spears for more than a month every spring.
The asparagus spears are straight young shoots of the plant, with scale-like tips. Later in the season, the foliage matures into an airy, light-green, fern-like cloud, which changes to a golden color in the fall. This perennial is typically planted from roots, or crowns, in early spring.
|Botanical Name||Asparagus officinalis|
|Plant Type||Perennial vegetable|
|Mature Size||5 feet tall, 3 feet wide|
|Sun Exposure||Full sun|
|Soil Type||Sandy, loamy|
|Soil pH||Acidic to neutral (6.0 to 7.0)|
|Bloom Time||Spring, summer, fall, winter|
|Flower Color||Pale yellow, greenish|
|Hardiness Zones||4 to 9|
|Native Area||Europe, Africa|
How to Plant Asparagus
Since you won't be harvesting for three years, asparagus requires some patience and preparation. Because asparagus is a perennial, you'll need to pick an out-of-the-way spot in the vegetable garden without competing plants. Asparagus also needs space, about 4 to 5 feet for each plant. They won’t spread out much the first couple of years, but once established they will quickly fill in. Heirloom varieties need extra space, as there are both males and female plants, meaning they will produce seeds and will self-sow. Newer hybrid varieties are bred to produce only male plants that don't produce seeds, so they need a little less space, as 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 for sale loose. 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 ultimately filled and 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, from which it is challenging to remove weeds. Add mulch to the asparagus bed to control weeds. Do not add any other plants to the asparagus bed—they dislike any 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 before you plant it. 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 before planting. 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. If you 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 50 degrees. Any frost after the shoots start growing will cause discoloration. 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.
Varieties 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 is made 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.
You should not begin harvesting your asparagus spears 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 the first year of planting, when the shoots aren't large. For healthy, well-established asparagus plants, patience is key.
You can harvest a few spears in the third year of growth. The plants are not fully mature, so harvest for 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. Your harvest time can extend to three weeks.
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 new growth starts. You can do this in late winter or fall. Removing the dead foliage in the fall offers the advantage of preventing problems, like asparagus beetles, from over-wintering in them. However, some gardeners like to leave the foliage for winter interest.
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. Hand pick 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.