When to Plant an Asparagus

If you haven't grown asparagus (Asparagus officinalis) before, you might not know that it's a perennial plant that spreads every year and can produce sweet, edible spears for as long as 15 years. You can start an asparagus patch from seeds, but beginning with dormant plants, called crowns, provides a harvest sooner. Asparagus is best planted in the spring, but timing can vary depending on the climate.

Asparagus continues growing year after year, gradually expanding its root system. The plants require a period of cold weather each year, when they die back and rest. Because of this, asparagus grows in U.S. Department of Agriculture plant hardiness zones 2 through 8, where sub-freezing temperatures are common during winter.

To have harvest-ready spears one to two years after planting, start with certified, disease-free, 1-year-old crowns from a nursery or garden center, choosing crowns with eight to 10 roots each. It's best to plant crowns in the spring, about four to six weeks before the average date of the last spring frost where you live. Don't plant crowns in fall, because they won't become established before winter arrives.

To plant asparagus crowns, dig a trench about 8 inches deep and 10 inches wide in a sunny part of the garden. Space crowns 12 inches apart, with the buds facing upward, and spread each crown's roots in the bottom of the trench. Cover the roots with about 2 inches of soil and water the plants. As the young spears appear, add more soil to the trench, gradually filling it in as the spears get taller, until the row of asparagus is about 2 inches higher than the nearby soil level.

Enough moisture is important during the first year to help asparagus plants develop a good root system, so water during dry spells, ensuring the plants get about 1 inch of water weekly, including rain.

You can also start asparagus plants from seed, growing them indoors and then transplanting them into the garden. Asparagus seed can take three weeks to germinate, so start seeds indoors about three months before your last spring frost. For example, if you want to start an outdoor bed in April, start seeds in January. Sow them about 1/4 inch deep in a sterile potting mixture in flats or small pots. Use pots that have drainage holes. Keep the seedlings in a sunny spot and their soil lightly moist until ready to move them outdoors.

Once weather warms, transplant the asparagus seedlings to a nursery bed and allow them to grow for one year. Early the following spring, move the plants while they're still dormant -- or crowns -- to their final location, planting them in a trench and gradually adding soil as they grow.

In addition to adequate moisture, weed control is crucial to give young asparagus plants a good start, so remove weeds often. Adding a 4- to 6-inch-thick layer of organic mulch, such as straw or grass-clippings, also helps keep down competing weeds, while conserving soil moisture.

Watch for asparagus beetles, small black insects that cling to asparagus fronds and destroy the leaves. Pick these off when you see them and drown them in a bucket of soapy water. Fertilize young plants each spring by mixing a handful of a 5-10-10 granular fertilizer into the soil around each plant, but be careful not to disturb the roots. Water well after applying the fertilizer. Whether you start with 1-year-old crowns or seeds, don't harvest spears from plants until their third year in the garden. Allow the plants to grow and produce leaves each year.