Cut asparagus spears before the tops start to open or fern out. Image Credit: Zedcor Wholly Owned/PhotoObjects.net/Getty Images
Unlike most garden vegetables which grow as annuals, asparagus (Asparagus officinalis) is a perennial plant found in U.S. Department of Agriculture plant hardiness zones 4 through 8. Older gardening guides often complicate asparagus gardening, making it seem more complicated than it really is. Planted in light, well-draining soil, in full sun, asparagus will thrive for ten years or more, making it one of the best investments you can make in the vegetable garden. Harvest begins a year or two after planting and continues each spring for several weeks.
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Young Plants
If growth was vigorous during the first growing season, you can harvest a few spears the following spring after planting. Young spears begin emerging when daytime temperatures rise to about 50 degrees Fahrenheit. Harvest the spears for two to three weeks only. The next season, harvest the spears daily for up to four weeks.This limited harvest saves most of the plants' energy for developing a strong root system.
Mature Plants
Mature plants — those three years and older — can be harvested for up to six weeks, depending on weather conditions. The spears are thickest in early spring when they first emerge. As the harvest continues and the weather becomes warmer, the spears become thinner. Stop harvesting when the spears are about the size of a pencil — usually in 4 to 6 weeks. Allow the spears to open and take on their fern-like growth, which can reach 4 to 6 feet tall. Cut the plants back in late fall or winter, only after they've turned brown.
Extending the Harvest
The spring asparagus season is fleeting — much too brief for asparagus lovers. To extend the harvest, grow two separate asparagus patches, suggests Clemson University Extension. Harvest one patch traditionally in the spring, but do not harvest the other one. Instead, allow it to fern out. Cut it down in mid-summer. The plants in this patch will produce a flush of new growth for two or three weeks, allowing you to enjoy fresh asparagus long after the asparagus season is officially over.
Harvesting Tips
To harvest asparagus, cut or snap it just above the soil surface. Don't cut the spears below the soil surface, which can damage the roots and make the plants more susceptible to disease. Harvest asparagus first thing in the morning when the plants are cool. Asparagus is highly perishable. Immediately plunge cut spears in ice water. Drain and pat them dry. Refrigerate cut asparagus and use it within a day or two for best flavor. The tasty spears can also be frozen for later use.
