Learning how to grow asparagus from seed is a fascinating journey. Asparagus plants are often grown from bare root stock crowns because it is quicker than growing from seed. However, even if you grow the plant from root stock crowns it can take up to 3 years before the plants are ready to harvest. Whichever method you choose requires patience.
There are a number of advantages to growing from seed. Not only is it cheaper, but seed grown crops are far less likely to suffer from transplant shock than nursery developed plants. Also, this method of asparagus cultivation often results in heavier harvests than crops started from root stock.
A popular vegetable, the plant is commonly grown from bare root stock. However you can also grow asparagus from seeds.
Cultivating from seed may take longer but, for many gardeners, it is a more rewarding process.
Growing asparagus from seed is possible for gardeners in many climates, including most areas of the United States and the lower areas of Canada. Gardeners in areas prone to extreme summer heat will struggle to cultivate this tasty crop.
Here is everything you need to know if you want to grow asparagus from seed.
How to Source Seeds
Before you begin to grow from seed, take the time to explore all the different varieties and cultivars that are available to you. Try to select varieties that best suit your growing conditions, this makes cultivation a lot easier. You should also select varieties that suit your personal taste.
Asparagus is a hardy perennial. Native to Western Europe it is suitable for cultivation in USDA zones 2-8. Once planted the plants are viable for 10 to 20 years.
Investing in a good quality seed from a reputable supplier is always worth a little extra expense. F1 varieties may be more expensive, and often come in smaller quantities, but they produce pleasingly high yielding plants.
Cheaper seed packets tend to be established heirloom varieties such as Mary Washington. These may have a better flavor but are usually not as heavy cropping.
The Jersey series is an all-male hybrid. It includes the hardy Jersey Giant cultivar, which is pleasingly robust in colder climates and Jersey Knight. This is a vigorous cultivar that is resistant to many common diseases including crown rot and fusarium wilt. A newer early season cultivar is Jersey Supreme. This is pleasingly diseases resistant and does particularly well in light or sandy soil profiles.
One of the most widely grown varieties is Purple Passion. This variety produces purple, sweet spears. The cultivar Apollo does well in both warm and cold weather conditions and is also pleasingly disease resistant. Finally the hybrid UC 157 is also disease resistant and does best in warm climates.
One of the advantages of starting from seeds is the large range of different varieties available. Some are even purple in color. However, this fades as the spears are cooked.
How to Harvest Seed
If you, or someone you know, is already growing asparagus you will
notice that uncut female plants, if allowed to, produce berries. During the fall these berries ripen, often turning bright red in the process.
Once the tops fall over they can be collected and hung upside down in a warm, dry position. Left in this condition the tops ripen within a week. Harvest the ripe seeds as soon as possible and store in a cool, dry location until ready for use.
To catch the seeds, place the plant tops in a brown paper bag. Alternatively place a bowl or container under the seeds, to them as they fall. This is an easy way to collect as much seed as possible.
While female plants produce berries they are not as productive as male plants. For this reason many gardeners choose to pull out the female plants as soon as they notice the berries.
Berries appear on female ferns. The berry is the seed of the plant. In the fall it turns bright red. Once ripe the seed can be harvested and planted the following year.
How to Sow
In the warmest climates viable seed can be sown directly into well worked garden beds. Hybrid varieties can be started either in the ground or in trays. However, heirloom varieties are more sensitive to transplanting. These are best sown into their final position, if possible.
Sow the seed undercover indoors or in a greenhouse from mid-February onwards. The soil temperature should be between 70 and 85 ℉.
Try soaking the seed for a couple of hours before planting. This softens the shell and helps to encourage germination. Plant each seed half an inch deep in small, 2 inch pots. Place in a bright position, or under grow lights.
In warm conditions germination occurs within 4 weeks. In cooler, or less ideal conditions this process may take slightly longer. If successful you should see signs of germination within 2 to 8 weeks.
Following germination keep the young plants watered. Don’t allow them to dry out.
When the seedlings are 10 to 12 weeks old begin to harden them off. Harden off as gradually as possible. Growing from seed is a long process. Exposing seedlings to extreme temperatures too quickly can cause them to fail.
Once the last frost has passed, plant out in well worked, fertile soil. This can be as late as May or June in some climates. Remember this is a long process, take your time and don’t rush your seedlings. Allow the seedlings plenty of time to acclimatise to their permanent position before transplanting. They will reward your patience later on by growing into strong, healthy plants.
Starting in the Ground
If you are sowing straight into a bed, keep the bed weed free. Weeds can grow quickly, smothering young plants. Following germination keep the seedlings well watered, especially during dry periods. New raised beds should be filled with fresh, good quality potting soil.
When the seedlings are large enough to handle thin out to a spacing of about 2 inches, depending on the variety. Thin out again when the seedlings reach 6 inches to a spacing of about 1 ft. The exact spacing varies between varieties, check the seed packet for exact distances.
As the plants grow, continue to keep them well watered and the beds weed free.
Where to Plant
Growing asparagus from seed, like planting root crowns, requires well draining, fertile soil.
The ideal position for many gardens is on the north or eastern side of a plot. This means that mature ferns won’t shade other crops. While yields are heaviest in full sun positions, asparagus can tolerate partial shade positions.
To minimize the chances of soil-borne diseases targeting your crop try to plant or sow in a part of the garden that has never been cultivated before. A new raised bed is also ideal. Adopting a simple form of crop rotation also helps to keep both the plants and the soil healthy and pest free.
While asparagus tolerates all but the heaviest clay based soils the plants do best in sandy loam based soils. Working the soil over well before planting can improve drainage and encourage the plants to grow.
The pH profile should ideally be between 6.5 and 7.0. While the plants grow in soil conditions outside the ideal, they struggle in extreme soil profiles. If you are unsure of the profile of your soil, why not invest in a soil testing kit? Liming the soil will help to raise the pH level. To lower the pH levels work in sulfur.
How to Transplant
Plant each seedling about 4 inches deep.
Space the seedlings 8-10 inches apart. If you want the plants to produce thicker spears space them 12-14 inches apart and 6-8 inches deep.
After planting, water well and protect from slugs or snails.
Caring for Asparagus Growing from Seed
Keep the soil moist, apply about one inch of water each week if it doesn’t rain. As the plants grow, cover the crown with soil.
Fertilize each spring with 1 or 2 cups of complete organic fertilizer per 10 ft row. Dig the fertiliser in gently trying not to damage the root system too much.
Planting tomatoes or tomatillos nearby can help to protect young plants. This is a popular companion plant combination. Tomatoes and tomatillos repel the harmful asparagus beetle. Additionally, asparagus plants repel the nematodes that can attack members of the tomato family. Calendula, or pot marigold, and petunias are also useful companion plants.
Mound soil up around growing spears. This prevents water from pooling and causing crops to rot.
Allow the plants to grow and refrain from harvesting until the third year. Each year allow the plants to set their ferns before cutting the ferns down to a height of about 2 inches in the late fall.
During the winter months, allow the plants some exposure to freezing temperatures. This encourages the plants to become dormant and return stronger the following spring. If you do not experience freezing temperatures, withhold water. An enforced period of drought has the same effect.
Continue to care for your plants in the same way until the third year. You can then begin to harvest the spears. The harvest season lasts for between 8 and12 weeks, depending on the productivity of your plants.
How to Deal With Common Problems
Fusarium wilt and crown rot can both affect asparagus plants.
Fusarium wilt causes plants to decline as well as shortening lifespans. During the spring, wilt can, as the name suggests cause the spears to turn brown and wilt. Many varieties of asparagus are now resistant to this issue, check the seed packet before planting.
Crown rot, as the name suggests causes the crown to rot. Once it takes hold, it slowly destroys a plant. Again, many types of asparagus are now resistant to this issue.
Rust diseases, causing small orange patches to appear on the ferns and spears of the plant. This is often caused by warm temperatures and high humidity. Correctly spacing the plans and watering only the base of the plant can prevent this. There are also rust-resistant varieties available.
Common Pests and How to Cure Infestations
Asparagus beetles, both common and spotted varieties can lay eggs on young shoots. If allowed to hatch the larvae will cover the plants before infecting the soil. Brush off any eggs that you notice. Insecticidal soaps can also be applied.
A more natural solution is to encourage ladybugs to your garden. These eat a number of bugs such as aphids, helping to keep your crops healthy and problem free. If you want to encourage more helpful bugs to your garden why not build a bug hotel in a shady corner?
Thrips can also be destructive. To identify an infestation place black paper below a fern and shake. If thrips are present you will notice the light-colored pests falling onto the paper. While heavy rain can wash the pests away a blast from a hosepipe or an application of insecticidal soap are just as effective.
How to Harvest
After three years your asparagus plants should be established and productive.
In the first year asparagus crowns should only be cut during a 10 day period. This may seem frustrating but limiting your harvesting now helps to strengthen the plants. This benefits the plants and results in better yields in the years to come.
To harvest use a sharp knife to cut the spears down to about 1-2 inches above the ground at least 2 inches above the crown. Special asparagus harvesting tools, such as the Zenport Asparagus Knife can also be used. These are purposefully designed to enable you to easily harvest spears cleanly and without harming the plant.
In the second year you can harvest the plants for 2 weeks.
Gradually increase this length of your harvest every year until you are eventually harvesting over a 6 week period.
Growing from seed requires patience. Wait until the third year before beginning a gradual harvest. When you do harvest, only cut spears that are thicker than a pencil.
Cease cutting when the spears are noticeably thinner. Don’t cut spears that are thinner than a pencil.
Most established beds can be harvested from mid-April until the middle of June. This may differ slightly in some areas depending on USDA zones and climates.
Storing Fresh Asparagus
Asparagus is best used fresh.
Harvested spears can be wrapped in a damp paper towel and placed in a perforated or open plastic bag. Place this in the coldest part of your refrigerator. In this condition asparagus spears can be kept for up to 4 days.
Don’t seal the bag. Cut spears emit gasses. In a sealed environment these gasses can cause the spears to spoil.
If you only want to store the spears for a few hours stand them upright in a shallow pan of water. Place the pan in a cool location, away from direct sunlight.
Growing asparagus from seed may take longer than other cultivation methods but it is a pleasingly rewarding process. It also offers you a greater variety of choice.
While growing asparagus from seed is a time consuming process it is ultimately a rewarding one. More affordable than purchasing root stocks, this method also offers you a greater variety of choice. Your time and patience will be rewarded with the taste of fresh asparagus, easily one of the best things you can harvest from your own garden.
Jen is a master gardener, interior designer and home improvement expert. She has completed many home improvement, decor and remodeling projects with her family over the past 10 years on their 4,500 sf Victorian house. She is also a passionate farmer who keeps goats, chickens, turkeys cows and pigs on her farm, and an instructor for her community’s Organic and Sustainable Farming project.