Site and SoilSince asparagus is a perennial, you'll need to pick an out of the way spot in the vegetable garden, an area you can till around. Asparagus also needs space, about 4-5 feet for each plant. They wont spread out much the first couple of years, but once established, they will quickly fill in.
Asparagus is not terribly particular about soil pH. Anywhere in the range of 6.0 to 7.0 would be fine. It is a heavy feeder though and much prefers full sun. A word of caution about weeds - get them while the asparagus plants are young. Asparagus roots form a tightly woven mat, from which no weed can be removed intact.
Seed or Crowns? What is a Crown, Anyway?
You can grow asparagus either from seeds or from crowns. Asparagus crowns are really just the base and roots of a one-year old plants. Most people find it easier to grow from crowns, which are readily available in the spring. Unlike many plants, the roots on asparagus crowns can withstand some air exposure and you will usually find them for sale loose. They should still look firm and fresh, not withered or mushy.
In warmer climates crowns can be planted in the fall. Early spring is the preferred time for cooler climates, about 4 weeks before the last expected frost date. Crowns can handle some frost because they are below ground.
When and How to Plant Aspargus
Asparagus is usually planted in rows, since you are going to dig trenches to plant them in. Start with a tench that is about a foot deep and 1 ½ feet wide. Working some compost into the bottom of the trench will get your plans off to a good start. Then make small mounds, about 6 inches high, along the bottom of the trench about every 18 inches.
Spread the roots of each crown over the mounds and fill in the trench until the crowns are covered with 2-3 inches of soil. As the plants begin to grow, you can gradually fill in the remainder of the trench.
If you choose to start asparagus seeds, start them indoors about three months before your last expected frost date. After three months, they should be about 12 inches tall and ready to plant outside. At this point, treat them the same way you would crowns.
Keeping Asparagus Growing - Maintenance and Harvest
Now you have to be patient. For the first two years you won't actually harvest any spears. Allow the foliage to grow and feed the plant. Keep the plants well watered and weed free and top dress with compost or manure. The plants are actually very attractive and ferny, turning a lovely gold color in the fall. Many people with limited space use asparagus as a border or ornamental hedge, harvesting just enough for their needs. By late winter or early spring it is safe to cut the old foliage back in preparation for new growth.
By the third year you should be getting good, finger sized spears, ready for picking. Some people snap their spears off, some prefer to cut. If you are cutting below the surface, be careful not to damage any emerging shoots. As a general rule, shoots should be about 8 inches long and the scales on the tips should not yet have begun to open.
In year three you can harvest for up to 4 weeks, then let the plants gain some strength. After that, feel free to harvest until it gets too warm for the spears to thicken.
Not many insects are interested in asparagus. The asparagus beetle feeds on the foliage, but can be easily controlled by hand-picking, if started early.
Rust used to be a major asparagus problem, but most modern varieties have been bred for resistance to this fungal disease. A more likely problem is fusarium wilt. Your best defense here is offense. Look for certified disease free crowns and keep them growing vigorously.