How To Grow Asparagus From Seed

While growing asparagus from seed takes a little longer to enjoy the first harvest, the long-lived perennial offers years of fruitful returns. Seeding asparagus is an efficient way to start the feathery-fronded spears, and it’s how the vegetables traveled to America with colonialism after 2,000 years of cultivation. 

Asparagus is one of the earliest spring vegetables. The fresh, crisp stems grow quickly and reach peak readiness in cool conditions. It’s a cold hardy, easy-care perennial in the right spot, with a quick-growing bounty once mature. It takes patience to achieve the first yield while healthy plants develop sturdy roots, but sowing seeds now sets the foundation for harvests in seasons to come.

Growing Asparagus From Seed

The two ways to start asparagus are from crowns (one or two-year-old roots) and seeds. Seeds grow horizontally in trenches and send up vertical shoots. Crowns have a headstart on the seeds and are ready to harvest two years after planting. Seeds take three years to develop before they’re ready for eating. Once established, the cold-hardy vegetables produce for years in USDA zones 2-9.

Asparagus spears grow quickly in early spring. By summer, they’re ready to set fronds to continue growing and developing robust roots for future seasons. The harvest season is about two months in the spring, and the ferny upper growth can form over the rest of the warm season.

Plant Selection and Popular Varieties

Asparagus plants are dioecious, meaning they’re either male or female, and both are edible. Female plants produce red berries and have thicker shoots, while male plants yield more spears, smaller and more uniform. Most hybrids are male plants. Since they don’t use energy to produce seeds, they’re longer lived and more productive in spear production.

Many seeds are hybrids and mostly male varieties that perform well. When selecting seeds, know your growing zone. If you live in a very cold climate, opt for the hardiest selections like ‘Millenium’ and ‘Mary Washington.’

‘Millenium’

‘Millenium’ is a favorite for performance, cold hardiness, yield, and flavor. It produces uniform spears with tight tips.

The top performer does well in areas with long winters. It’s also disease-resistant to asparagus problems like rust, Fusarium, and crown rot.

‘Mary Washington’

This heirloom variety is a reliable performer and female selection. Long, straight, upright stems are rich and dark green. Through open pollination, ‘Mary Washington’ produces ornamental seeds (red berries) to expand the colony, though offspring might not be true to type if you have multiple varieties. While the stems are delicious, asparagus seeds contain toxins and aren’t edible.

‘Mary Washington’ resists common asparagus-growing issues and diseases. Another good option for cold climates, it grows across varying conditions. ‘Martha Washington,’ too, is a top heirloom.

‘UC-157’

This hybrid out of the University of California Davis is vigorous and disease-resistant. Among the most widely planted, it yields three to five fast-growing stems at a time. Heavy, early yields and uniformity in size and color make it productive in the home garden and for the market.

‘Purple Passion’

Deep purple tones make this an intriguing ornamental addition to the edible landscape. When cooked, spears turn bright green. The plump stems hold more sugars than green selections for a mild flavor and have a low fiber content.

Thicker than green varieties, stems emerge later in the season, giving the opportunity to stagger the harvest with early and late producers. Emerging later also protects sensitive shoots from early frosts. Pick when stems are less than five inches.

Siting

Since the ferny perennials are long-lived (15 years or more) and have deep roots, siting takes careful consideration. Many gardeners start seeds in a single patch and then transplant seedlings to their permanent locations. The seeding patch should be weed-free, level, and have sandy, well-draining soil.

Asparagus officinalis tolerates a variety of soil types as long as they’re well-draining. They need regular moisture as roots establish and don’t flourish in overly saturated situations. Full sun and organically rich soils are optimal. It helps to have a soil test in advance of transplanting to indicate any beneficial amendments. A soil pH between 6.5-7.0 is best for asparagus; they don’t thrive in highly acidic compositions. If you have poor draining soils, consider growing it in raised beds.

The tall fronds reach four to eight feet, depending on the variety. In the vegetable garden, situate them where they won’t shade other specimens (like the north end of a bed). With late-season frosts in cold climates, emerging spears benefit from frost protection or a protected site.

Companion plants for asparagus support the perennials through beneficial features like deterring pests such as asparagus beetles. Tomatoes, eggplants, basil, and dill make good partners. 

How to Sow Asparagus Seeds

While growing from crowns is the primary way to grow asparagus, starting them from seed is a cost-efficient, fun way to get them going. Prepare the seeding patch for spring planting. Keep it weed-free throughout their development, as young seedlings don’t tolerate competition well.

Plant asparagus seeds one inch deep and two to three inches apart. If using rows, space them one foot apart. Keep soils evenly moist, and they’ll germinate within a few weeks. Thin seedlings to six inches apart for ample air circulation and growing room.

You can also start asparagus seeds indoors, using biodegradable pots to minimize transplant disturbance. With a lengthy germination time, start them in late winter for transplanting in late spring. Ideal temperatures are 55-60°F (13-16°C). To speed up germination, soak seeds overnight before sowing.

February is a prime time to grow asparagus seeds indoors – aim for about eight to ten weeks before you plan to transplant. Move seedlings to the garden when soil temperatures are near 60°F.

Regular moisture throughout the growing season fosters the best growth. As temperatures cool in the fall, add a layer of clean straw or leaf mulch to insulate the young roots over the winter. Pull the layer back from the crowns as temperatures begin to warm in spring. Temporarily lifting the layer lets sunlight warm the roots for earlier emergence.

Planting the Crowns

As crowns are one-year-old roots, the seedlings are ready for transplanting the following spring. Move them from the patch to their garden home before they emerge (usually April-May for northerly climates and earlier in warmer zones). 

Planting the crowns involves digging a six to twelve-inch trench for placing the roots horizontally. Lay them in the trench so the crown buds are about one foot apart, with trailing roots leading to the next crown. Cover them with a few inches of soil, leaving the rest for infill as the fronds develop.

Water them in, and keep the roots evenly moist as they establish. After a few weeks, spears develop. When they reach four inches tall, backfill with several more inches of soil.

Weed, Irrigate, and Fertilize

Young seedlings and transplants have small root systems. Even when established, regular weeding reduces crowding and competition for nutrients, moisture, and sunlight. Heavy weed pressure depletes the roots and shoots of growing essentials.

About one inch of water per week is usually enough to support asparagus in the growing season. Whether from rainfall or irrigation, this standard amount (average for many shrubs and other perennials) is generally sufficient. Asparagus doesn’t often show signs of drought stress, but supplemental irrigation helps during dry spells or heat waves. If soils are sandy, more frequent irrigation may be necessary (and less for heavy or clay soils that hold water).

A fertilizer application when planting the crowns and in spring helps boost nutrition. At transplanting, apply a balanced granular or slow-release fertilizer. Topdress with compost in late winter/early spring for the added benefits of soil nutrition, aeration, and moisture retention. In rich soils, you won’t need extra fertilizer. In leaner soils, use the same balanced fertilizer application or one higher in phosphorous if plants lack vigor. Apply it alongside the plant (sidedress), scratching it in lightly to about an inch, avoiding shallow surface roots.

Harvest

Asparagus is easy to grow from seed or crown, but it takes patience to get to that first yield. After seeding and then transplanting the following year, let fronds develop rather than harvesting. Shoots will emerge and are best left to grow into leaves to photosynthesize and build energy for robust, starchy roots and successional seasons of growth. Harvesting too early leads to weak, thin future growth. 

To harvest, snap the spears just below the soil surface. Choose young, slender stems over thicker, woodier ones.

Storage

Fresh asparagus is tender, crisp, bright, and delicious just after harvesting. It’s the hallmark flavor of early spring. Spears also store for about a week in the refrigerator. 

If you have a large bounty, freeze or can the shoots for future enjoyment. They’re also zesty pickled.

To freeze asparagus, blanch them first, and freeze whole spears or cut them into pieces. First, wash the spears and cut off the woody end. Blanch them in boiling water for two to four minutes (for thick stems), followed by an ice bath for the same length of time.

To keep them accessible for use in small amounts (i.e., keeping the pieces from freezing together), place them on a parchment-lined baking sheet after blanching and cooling. Freeze the sheet until the pieces are firm, then transfer them to an airtight container or baggie for long-term freezing.