Starting Asparagus from Seed

Asparagus is a long-lasting, nutritious perennial that keeps on giving year after year. However, crowns can often peter out after only a few seasons, whereas asparagus plants started from seed can last up to 15 years.

While purchasing year-old crowns for transplant is the most common way to establish an asparagus patch, many backyard gardeners and homesteaders start plants from seed. With a proper seed-starting set-up, this method is cost-effective, rewarding, and will provide you with the most vigorous possible plants. Plus, once you know you can successfully germinate the seeds, you can produce crowns for sale, boosting your income. 

Growing asparagus plants from seed is perfect for patient gardeners who are in it for the long haul. When you head to the garden and complete your first asparagus harvest, then taste the fruits of your labor after four years of care, you’ll know the extra effort was worth it. Let’s learn more about the asparagus seed, then discuss how to start plants from seed successfully. 

Understanding Asparagus Seeds

Since growing asparagus from crowns is most common, most people don’t know that their seeds are readily available on many seed company’s websites and are relatively inexpensive. If you already have an established patch of heirloom varieties, you can save seeds after harvest to keep the plant’s genetics alive and thriving. 

Preparing to Germinate Asparagus Seeds

While starting asparagus seeds isn’t tricky, choosing the right variety for your climate and setting up an efficient seed-starting area is critical. Let’s discuss a few things you can do before sowing seeds to ensure success. If you are new to seed starting, our article, Seed Starting 101, explores all the basics.

Step 1: Choosing the Right Seeds

It’s a fact that all crops won’t perform well in every garden due to soil type, climate, elevation, and growing zone. Asparagus will perform well in most climates, except where it’s extremely hot and dry.

It prefers mild weather and areas with a cold winter of at least three months to ensure dormancy. If you’re in USDA growing zones 3 to 10, there is an asparagus for your growing region. Heirloom varieties are marked below with an asterisk.

Cold climates: 

• ‘Millennium F1’: long-living, productive, tender spears

• * ‘Mary Washington’: green stalks with purple tips 

• ‘Waltham Washington’: hardy, rust-resistant, dark green 

• ‘Guelph Millenium’ F1: consistent and uniform, high-yields, bred in Canada 

• ‘Burgundine F1’: purple, sweet, tender 

Warm climates: 

• ‘UC 157 F1’: high-yielding, sweet, uniform, non-stringy, rust and fusarium wilt-resistant 

• ‘Atlas F1’: early, vigorous, disease-resistant, thrives in hot climates 

• ‘Princeville’: easy pick for beginners 

Reliable and performs well across zones: 

• ‘Jersey Supreme F1’: early variety, disease resistant, zone 3 to 8

• ‘Jersey Knight F1’: great vigor, resistant to many common asparagus diseases, zone 3 to 8

• ‘Jersey Giant F1’: mild flavor, extremely productive, cold hardy 

• ‘Apollo F1’: rust-resistant

• * ‘Purple Passion’: one of the sweetest, loses its purple color when cooked 

• * ‘Precoce D’Argenteuil’: tender, high-quality, disease-resistant 

We mention members of the Jersey series here because they are well-known and popular, but unfortunately, the line has been discontinued by its producer. The University of Minnesota Extension offers acceptable replacements here. 

Home growers prioritizing taste and uniqueness over production and uniformity may prefer an heirloom variety. In contrast, farmers growing for market or restaurant sales may select hybrids to ensure a consistent look and flavor. 

Step 2: Equipment and Materials

Gather seed trays or containers, potting mix and additives, humidity domes, and an adjustable heat mat. Ensure everything is sanitized, including any tools you may use for scarification. Any surface or tray potentially carries disease from previous seasons' seed-starting or pruning, which can lead to failure to germinate or the contraction of disease and death. Before starting, read How to Use a Humidity Dome for Seed Starting and How to Use Heat Mats for Starting Seeds to ensure proper usage of humidity domes and heat mats. 

Step 3: Pre-Germination Preparation

To adequately stratify your selected seeds, place them in an airtight container with a damp towel and then in the refrigerator for three to four weeks. Cold stratification mimics dormancy, and when the seeds emerge from the cold, they receive a signal that it’s time to wake up. Germination requires cold stratification. 

Soak your seeds for several hours or overnight before sowing them. Soaking softens the hard exterior and leads to quicker germination, which allows the seed to use its energy to grow and not simply emerge. If you plan to sow seeds directly in the outdoor garden soil, we highly recommend you soak them, as they will tolerate the cooler soil better than unsoaked seeds. Some believe soaked seeds lead to stronger and more resilient asparagus seedlings. If you’re new to the process, experiment with both ways and decide for yourself! 

In addition, you may scarify seeds before soaking them by gently scratching or scarring one of the ends with an emery board or sandpaper. Scarification allows the seed to absorb water, initiating germination and allowing it to sprout more quickly.

The Germination Process for Asparagus Seeds

You can sow asparagus seeds indoors or directly in the ground, and each has benefits. We’ll discuss both here and how to create the perfect environment for good germination. Start seeds indoors 12 to 14 weeks before the last anticipated frost. 

Step 1: Sowing Seeds Correctly

While your seeds are soaking, prepare your workstation. Your potting mix should be loose and well-draining, with a pH of 6.5 to 7.0. Add coconut coir or perlite to a loamy potting mix to help maintain soil moisture, improve drainage, and add neutral organic matter. Asparagus will not tolerate high acidity. Fill enough containers with soil so that each seed has its own. We recommend our 4-cell plug trays with a 1010 tray beneath or 6-cell ones with a 1020 tray beneath. These pots offer plenty of space for asparagus roots to form, and their air-pruning features will ensure the seedlings remain healthy. 2.5” seed-starter pots would work well, too. 

Sow one seed per cell or container about ½ to ¾-inch deep, but do not cover with soil as light is required for germination. Water the containers so the soil is thoroughly moist but not soaked. Bottom-watering will prevent the seeds from becoming displaced, contracting fungal diseases, and damping off. Our article, Bottom-watering Seedlings and Microgreens, provides more information.

Alternatively, growers can sow seeds directly in their garden. Choose a flat, sunny area in the spring and sow seeds about ½ to ¾-inch, leaving a few inches between seeds and a foot between rows. The seedlings will grow in this area for the first season in an asparagus nursery bed. The seedlings will grow here for the first year, so keep the area weed-free and well-watered. The garden space will serve as an asparagus nursery bed for the first season. Mulch the area before winter to protect them from frost damage. Don’t worry; they are strong enough to push through it in the spring, similar to rhubarb and garlic. 

Step 2: Creating the Perfect Germination Environment

Place containers on a temperature-controlled heat mat between 70° and 85°F (21° to 29°C) until germination occurs. Use humidity domes to keep moisture in and humidity levels high. Place them in a sunny spot or under grow lights. 

Step 3: Monitoring Progress

Germination takes an average of 21 days, sometimes 56 days. The time depends on the soil and air temperature, variety, seed viability, and light provided. Water the soil about an inch per week so it remains moist. Overwatering may lead to fungal disease and root rot, so while you should water regularly and consistently, avoid letting the soil become waterlogged. 

Common issues that may lead to delayed or lack of germination include: 

• Unsoaked and unstratified seeds 

• Cold soil

• Inconsistent temperatures

• Too much or too little water 

• Unviable seeds 

• Pest problems due to soggy soil 

• Lack of light

• Crusty soil surface

• Weed competition when planted directly into garden soil 

Monitor regularly for pests, fungal issues, and germination. Seeds need light to germinate, so ensure they are receiving at least eight hours a day. Bottom water to reduce seed displacement, pest issues, and fungal diseases. Provide light air circulation with a fan on a low setting to prevent crusty soil and keep pests away. 

Caring for Seedlings After Germination

Care for your new seedlings properly to ensure they live a long, healthy life. 

Step 1: First Steps After Sprouting

Once the seeds sprout, which can take 10 to 56 days, slowly decrease the temperature to 60° to 70°F (15° to 21°C) and keep them under direct grow lights. As the seedlings grow, raise the lights to remain several inches above the highest point. Provide a minimum of eight hours of light a day. If you have a heated greenhouse, place the seedlings in direct sunlight. Keep a fan on the seedlings to promote strong stems and prevent the soil from becoming crusted over. 

Step 2: Thinning Seedlings for Better Growth

Thin seedlings to one per cell by gently pulling unwanted seedlings out, leaving the healthiest ones to continue growing. Pinch the base of the seedling with your thumb and index finger, and ensure others don’t come out with it. Thin hybrid seedlings in the ground to six-inch spacing, 12 inches for heirlooms, which will drop seeds in future seasons. 

Step 3: Transplanting to Larger Containers

Like many young seedlings, wait until your asparagus babies have a set or two of true leaves to minimize damage. Transplant seedlings with all the soil from the previous pot to avoid transplant shock and keep them in the same environment if possible. Choose a container several inches deeper and wider if you require more time before transplant, or plan to keep them in your greenhouse until the following spring. 

Transitioning Seedlings to the Garden

Seedlings should be ready to transplant when they are about 12 weeks old and the risk of frost has passed in your region. 

Step 1: Preparing the Garden Bed

Select a place in the garden that is level, well-draining, and receives full sun. Lack of enough sun will result in thin, spindly spears. Soil test before planting day to ensure the pH is 6.5 to 7.0 and work in lots of organic matter to help drainage. Remember, asparagus roots remain shallow and form a dense web, and do not tolerate weed competition. Clear the area of weeds by covering it with a silage tarp for several weeks or months to kill tiny weed seeds that come up to germinate. Read more about the process in our article, Using Silage Tarp for Organic Weed Control and Bed Prepping. 

Fertilize the soil with a balanced fertilizer (10-10-10) to ensure proper nitrogen, phosphorus, and potassium levels. Access to adequate soil nutrients, sunlight, and well-draining soil are critical to growing asparagus. 

Step 2: Hardening Off Seedlings

If you’ve started seeds indoors instead of directly in the ground, you must harden them off before transplanting them. Hardening off introduces outdoor conditions to acclimate young plants to fluctuating temperatures, precipitation, and wind, decreasing the risk of stressed plants and transplant shock. Start this process about a week before the transplant on a cloudy, mild day, preferably without much wind or rain. 

Keep them outside for about half a day, then bring them back in, increasing the time outside each day until they remain outdoors overnight. The first night outside, you may cover them with frost blankets to decrease stress. Monitor them for signs of stress, adjust as needed, and gradually cut back on water each day. 

Step 3: Planting in the Ground

Build up a raised bed of soil in an in-ground garden, alternatively, you can use a wooden or metal raised bed. Incorporate the necessary amendments and lots of organic matter like compost into the top few inches of soil. Create a mound several inches high with your hands, then place one seedling every 12 to 18 inches atop the mound, spreading the roots over the mound. Then, bury the whole area with about two inches of soil. Some growers leave the top inch out of the soil, but it’s not required. Add more soil every few weeks as they grow. 

Alternatively, dig a 6 to 12-inch deep trench, placing the trench soil off to the side to use later. Build 12-inch tall mounds with amendments and compost, then transplant one seedling every 12 to 18 inches, one per mound. The height and high organic matter levels help increase drainage. Cover each crown with just two inches of soil, adding a few more inches every few weeks as they sprout and grow. This slow bury method helps the plant conserve energy, which has to emerge through only a few inches of soil at a time. 

Remember that heirloom varieties spread underground via their rhizome, and seeds are dropped each season. Leave them more space to expand, whereas male-only hybrid varieties only need about a foot between plants. Proper spacing will ensure high-yielding, long-living, healthy plants. If no rainfall occurs, water one to two inches weekly. 

Mulch moderately with compost to ensure weed pressure stays low and to keep the soil temperature consistent. Each year, mulch with organic straw before winter to protect the crowns from frost damage. 

Cultural pest control includes coffee grounds around plants, insecticidal soap, strong blasts of water, and diatomaceous earth. Allowing companion plants to flower will attract beneficial insects and bees. When fronds are left to expand in the late summer and fall, they become a popular hangout spot for bees, who are attracted to the pollen and nectar in the buds. Cut back fronds when yellowing begins to prevent the asparagus aphid and other pests from laying eggs to overwinter.

Companions for Asparagus 

While asparagus does not tolerate competition from weeds, there are a few plants it will tolerate being planted near or with; some will even offer benefits. 

• Basil, parsley, and tomatoes may help repel asparagus beetles by releasing solanine.

• Asparagus repels nematodes, which are harmful to tomatoes. 

• Get two crops from the same space by planting early-season spinach nearby when your asparagus patch is establishing. 

• Transplant late-summer lettuce under tall asparagus ferns to take advantage of the shade. 

Pro tip: Do not plant potatoes or alliums near your asparagus. 

FAQs About Germinating Asparagus Seeds

How difficult is it to grow asparagus from seed compared to crowns?

Starting asparagus seeds is not difficult, especially for experienced gardeners. However, it takes much more patience and time than planting a crown. 

What is the best time of year to start asparagus seeds indoors?

If you have an indoor, warm seed-starting area, sow seeds between February and May, 12 to 14 weeks before your last frost. 

How long does it take to grow asparagus from seed to harvest?

Year one is the year you plant the crown in the ground. You’ll notice spears beginning to sprout in year two, but harvesting them will be detrimental to the plant’s long-term productivity. You can harvest a small number of spears in year three to taste your crop but leave most of them to continue to allow the plant to establish. Choose a spear six to ten inches tall before they have formed ferns and cut below the surface, taking care not to damage the roots. 

Most varieties will be ready for harvest regularly after the fourth year in the ground with proper care and fertilization. Check the plot every few days, as they’ll grow quickly with warming temperatures. The harvest window should be six to eight weeks at this point. Quit harvesting when the spears sprouting are thinner and allow the plant to form fern foliage. Spears have gone by and will not be ideal eating quality if they begin to fern. The harvest size will increase yearly after the fourth with proper care and fertilization. 

Can I grow asparagus seeds directly in the garden instead of indoors?

Growers with flat, sandy garden space can sow seeds directly in the garden soil in the spring. Leave two to three inches between seeds and a foot between rows. The garden space will serve as an asparagus nursery bed for the first season. Keep the area watered and weed-free, allowing the crowns to establish throughout the season. Mulch the area before winter. Dig up the crowns the following spring, keeping as much of the root system intact as possible. Move the crowns to the prepared garden area to live permanently, or gently wrap and refrigerate them before selling them. 

What are the most common germination problems with asparagus seeds?

• Planting the seeds too deep. Place asparagus seeds a ¼ inch under the soil surface. Seeds planted too deeply may be delayed or fail to germinate. 

• Over or under-watering. Water consistently during germination, which may take up to three weeks. Avoid dry or soggy soil. Provide about an inch of water per week unless rainfall occurs. 

• Soil temperature should be at least 70°F (21°C) and remain consistent so seeds evenly germinate. 

How can I tell if my asparagus seeds are viable before planting them?

Viable seeds are dark, hard, and smooth. Mushy, soft, discolored seeds are unlikely to be viable. If you have seeds to spare, place 10 to 20 in a damp paper towel and a plastic baggie. Place them on a heat mat for up to three weeks. The percentage of seeds that germinate after this time indicates the germination rate.