Asparagus produces young edible shoots in the spring and is the best-known and most widely planted perennial vegetable. If managed correctly, it can provide several months of fresh eating and many years of reliable growth. For those who have seen asparagus only on their dinner plate, the tall, ferny growth of mature asparagus plants comes as a surprise.
Because asparagus will occupy its space in the garden for a long time, it makes sense to build proper soil in advance. One of asparagus's requirements is a near-neutral pH, between 6.7 and 7.0. While it will grow at lower pH, research conducted at Michigan State University shows that low soil pH is more conducive to fusarium wilt, a fungal disease. Keep the 6-foot height of the summer foliage in mind; don't plant asparagus where it will shade other crops. Choose a well-drained location in full sun.
Plant asparagus during its dormant period: early spring where winters are cold; fall or winter in milder climates. Dig a trench a foot wide and nearly as deep, incorporating plenty of compost and a handful of high-phosphate organic fertilizer. Space the crowns about 18 inches apart and cover them with 2 to 3 inches of rich soil. Add more soil as the plants grow to gradually fill the trench.
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Asparagus has been a staple in vegetable gardens for centuries. 'Mary Washington' and other Washington varieties are traditional favorites, grown from seeds or crowns and including both male and female plants. Rutgers University introduced the hybrid Jersey strains, such as 'Jersey Giant', 'Jersey Knight', and 'Jersey Supreme'. These all-male hybrids are said to be more productive because none of their energy is wasted on seed formation. Some varieties produce purple spears, which turn green when cooked.
Once planted, it's best to leave asparagus for 2 or 3 years before harvesting the first spears. In the fourth spring and thereafter, the plants should be vigorous enough to yield 8 weeks of harvested spears. Charlie Nardozzi, author of Vegetable Gardening for Dummies, offers a technique, dubbed the mother stalk technique, for extending the harvest of established asparagus beds. "Instead of harvesting all the spears as they emerge from the soil, allow three large spears per crown to grow ferns," Nardozzi says. "By leaving three spears, the crown is being constantly fed through photosynthesis in the ferns. You can harvest asparagus weeks longer than normal—right into August in Zone 6." Once the diameter of the new spears becomes smaller than a pencil width, stop harvesting and allow the foliage to develop.
Asparagus is susceptible to asparagus rust, a fungal disease that is evident when yellow to orange spots appear on the foliage. Avoid it by selecting resistant varieties, such as the Washington and Jersey cultivars. Asparagus beetles can appear later in the season and will weaken the roots by defoliating the ferns. Control by hand-picking the beetles. After frost, remove and destroy the dried foliage to eliminate sites for beetles to overwinter.
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