9 Soil Tips for Growing Better Asparagus

I‘ll never forget the flavor of the first fat spear of asparagus I snapped from my own garden. It was sweet and juicy, and it snapped under my teeth with only the slightest hint of that sulfurous, grassy flavor that you often find in store-bought asparagus. I had planted 10 crowns three years before in a wide mound of sandy soil in full sun. The asparagus thrived, and my education in growing this long-lived perennial delicacy began.

Asparagus is a fairly unique vegetable because in a healthy mature patch, you harvest first and grow later. The edible portion of asparagus is the spear, which pushes up through the soil from a deep, energy-storing root system. This spear wants to become a tall, billowy frond that captures sunlight to send back down to the root system, but you’ll pick spears young, before they have a chance to toughen and unfurl.

To cultivate a healthy crop, pay particular attention to the soil in your asparagus bed. Asparagus is deep-rooted and prefers sandy, well-drained soil—areas that stay wet will rot the roots and invite disease. Here are some additional tips for prepping and maintaining the dirt your asparagus calls home.

1. Load Up on Phosphorus:
Asparagus loves phosphorus. Composted manure, bone meal and rock phosphate are all good amendments to keep soil levels high in this nutrient.

2. Hold the Salt:
While asparagus is salt-tolerant and grows well as a perennial in seaside gardens, the occasionally recommended advice to add salt to an asparagus bed isn’t wise and can seriously damage soil quality.

3. Don’t Rotate Beds:
When happy, asparagus settles in for the long haul. It can live and produce for two decades or more, but it loathes having its roots disturbed for any reason, especially moving. Pick a location where your asparagus can literally put down roots, and avoid digging or deeply cultivating the soil around your asparagus patch.

4. Keep It Weed-Free:
Because asparagus is so long-lived, it’s especially important to rid your planting area of any pernicious perennial weeds. Invasive creepers, such as bermuda grass, bindweed, quack-grass and buttercup, are difficult to eradicate, but they’ll out-compete your asparagus stand and must be removed from the soil before planting. Monitor the asparagus patch seasonally to keep weeds at bay.

5. Top-Dress Every Spring:
Keep your asparagus patch performing well by top-dressing every spring with 2 to 3 inches of composted manure, followed by a 2-inch layer of loose resistant cultivars. Shredded arborist’s woodchips, straw and finished compost are all good choices. This top-dressing will provide the soil with nitrogen and phosphorus, as well as keep it weed-free and in good tilth.

6. Fertilize Twice A Year:
Asparagus is a relatively heavy feeder. While the spring top-dressing will feed and add organic matter to the asparagus patch, you’ll get even better results if you feed lightly in early spring and again in mid-summer with a high-phosphorus organic fertilizer, like fish meal, which has a typical N-P-K value of 8-12-2.

7. Minimize Disease and Pest Risk:
A patch of asparagus grown in well-drained soil is rarely bothered by disease, but fusarium wilt, purple spot, needle blight and asparagus rust can all infect your crop. If these diseases are known to be an issue in your growing region, planting resistant cultivars is essential. Your local extension program will know what issues tend to crop up in your area.

For asparagus growers everywhere, siting asparagus in an area with good airflow and practicing good sanitation is important to discourage pathogen and disease build-up in the soil. At the end of the growing year, cut down and hot compost or burn the fronds and clean up debris.

Asparagus’ most common pest is the asparagus beetle, which will often overwinter in the soil. Good sanitation and allowing hens access to forage for the beetle can help reduce a buildup of these pests.

8. Companion Plant and Cover Crop:
Asparagus enjoys being planted alongside other perennials, like rhubarb and fruiting shrubs, but avoid planting companions too close to minimize competition. The fronds of mature asparagus can reach 5 feet or taller, making this plant a great option for the middle layer of a stacked perennial bed.

To build soil fertility naturally, an established asparagus patch can be under-seeded with a low-growing, nitrogen-fixer cover crop, like crimson clover, and interplanted with phosphorus bio-accumulators, like yarrow. In some areas, both crimson clover and yarrow can be invasive, so select the right soil-improving bio-accumulators for your region.

9. Start Out Right:
Asparagus can be started from seeds or crowns—the crowns offering beginners a one- to two-year headstart on a harvest and often an ideal choice for beginning asparagus growers. However, if you want to start your asparagus from seed, sow it directly into well-drained, loose, fertile soil in a well-weeded, prepared bed after the soil has warmed enough to initiate germination—typically in April or May. Soak seeds in cool water or dilute compost tea for 1 hour before sowing, then space 8 to 12 inches apart. Cover seeds with 1 to 2 inches of loose, sandy soil and thin to an eventual spacing of 12 to 16 inches between plants. Keep soil moist until germination.

Alternatively, start indoors in late winter. Soak seeds in cool water or dilute compost tea for an hour, then sow seeds 1 inch deep in 4-inch pots filled with an organic potting mix that includes an organic, slow-release, balanced fertilizer (3-3-3 or 5-5-5). Keep the soil warm, and as soon as seeds germinate, set pots under full-spectrum grow lights or in a bright, sunny window or greenhouse, depending on outdoor temperatures. Transplant to the garden in mid to late spring when soil has warmed.

If you opt to plant crowns, keep in mind asparagus suffers some transplant. Plant crowns as soon after purchase as possible, in a prepared bed of well-drained, sandy soil. Dig a shallow, 6-inch-deep trench 12 to 18 inches wide and soak crowns for 15 minutes in cool water or diluted compost tea. Place the crowns 12 to 18 inches apart along the trench, spreading the roots out gently. Top with 2 to 3 inches of loose soil. When the shoots begin to appear (in several weeks to a month or more, depending on soil temperature), hill up around the growing crowns with another inch of soil. As the shoot grows, continue adding loose, sandy soil to the trench until it is filled.

Given the right early attention, asparagus is an investment that can really pay off. The first few years will require the right soil prep and a little babying to make sure the crop growing well, but after it’s established it’s a low-work culinary prize for the gourmet gardener.