Asparagus: Perennial Vegetable, Indoor Sow or Direct Sow, Bare Root or Potted Seedlings
How to Sow and Plant
Asparagus may be grown from seed sown early indoors and transplanted outside after frost, from seed sown directly in the garden, from transplanted seedlings in fall or from year-old bare roots in spring.
Sowing Seed Indoors:
- Start asparagus seeds indoors 8-12 weeks before outdoor planting date in spring in peat pots, plastic pots or trays. At least 2 x 2 inch cells works best.
- Sow seeds ½ inch deep in seed-starting formula.
- Keep soil moist at 70-75 degrees F
- Seedlings will emerge in 10-14 days
- As soon as seedlings emerge, provide plenty of light on a sunny windowsill or grow seedlings 3-4 inches beneath fluorescent plant lights turned on 16 hours per day, off for 8 hours at night. Raise the lights as the plants grow. Incandescent bulbs do not work because they get too hot. Most plants require a dark period to grow, do not leave lights on for 24 hours.
- Seedlings do not need much fertilizer, feed when they are 3-4 weeks old using a starter solution (half strength of a complete indoor houseplant food) according to manufacturer’s directions.
- Seedlings should be 6-10 inches tall with 4-6 stems with several buds coming from the crown when they are ready to transplant outside.
- Before planting in the garden, seedling plants need to be “hardened off”. Accustom young plants to outdoor conditions by moving them to a sheltered place outside for a week. Be sure to protect them from wind and hot sun at first. If frost threatens at night, cover or bring containers indoors, then take them out again in the morning. This hardening off process toughens cell structure and reduces transplant shock and sun burn.
- When selecting a site, keep in mind that asparagus is a perennial vegetable and the planting bed should not be disturbed. Early soil preparation is essential in order to establish a healthy asparagus bed. Asparagus prefers full sun and a good organic well drained soil.
- Space transplants 12 inches apart in a single or double row. Double rows should be 12-14 inches apart. Transplant before temperatures are 90 degrees F.
Sowing Directly in the Garden:
- Direct sow seeds in in spring when the soil is at least 60 degrees F.
- When selecting a site, keep in mind that asparagus is a perennial vegetable and the planting bed should not be disturbed. Early soil preparation is essential in order to establish a healthy asparagus bed. Asparagus prefers full sun and a good organic well drained soil.
- Prepare the soil by removing weeds and working organic matter into the top 6-8 inches of soil; then level and smooth.
- Sow seeds evenly and thinly 2 inches apart, ¾ -1 inch deep
- Firm soil lightly with your hand, water and keep evenly moist.
- Seedlings will emerge in 10-14 days at 75 degrees F, a little longer if the soil is cooler.
- Thin seedlings to about 12 inches apart when seedlings have at least two sets of leaves.
Planting Bare Roots in the Garden:
- When selecting a site, keep in mind that asparagus is a perennial vegetable and the planting bed should not be disturbed. Early soil preparation is essential in order to establish a healthy asparagus bed. Asparagus prefers full sun and a good organic well drained soil.
- Dig trenches 6-8 inches deep and 12-15 inches wide. Space rows 2 ½ - 4 feet apart.
- Set roots in the bottom of the trench, spacing crowns (centers) 18 inches apart in the row. Spread roots out as far as possible for best root establishment.
- Cover roots with 2 inches of fine soil and water well.
- Plants may take 6-8 weeks to emerge.
- Continue adding soil as the tops grow up, about every three weeks, until the trench is full, which should be about midsummer when planted in early spring.
Planting Seedling Plants in the Garden:
- When selecting a site, keep in mind that asparagus is a perennial vegetable and the planting bed should not be disturbed. Early soil preparation is essential in order to establish a healthy asparagus bed. Asparagus prefers full sun and a good organic well drained soil.
- Dig a hole for each plant large enough to amply accommodate the root ball.
- Set plants in the bottom, spacing centers 18 inches apart in the row. Space rows 2 ½ - 4 feet apart.
- Place the top of the root ball approximately ½ inch below the level of the surrounding soil.
- Fill with soil to the top of the root ball.
- Press soil down firmly and water.
How to Grow
- Keep weeds under control during the growing season. Weeds compete with plants for water, space and nutrients, control them by either cultivating often or use a mulch to prevent their seeds from germinating.
- Mulches also help retain soil moisture and maintain even soil temperatures. Put down a layer of newspaper 5-10 sheets thick between the rows (soak the papers in water first, so they won't blow away) and then cover the newspaper with dry grass clippings, aged bark mulch, weed-free straw, etc. Always keep mulches off of plants’ stems to prevent possible rot.
- Keep plants well-watered during the growing season, especially during dry spells. Plants need about 1 inch of rain per week during the growing season. It's best to water with a drip or trickle system that delivers water at low pressure at the soil level. If you water with overhead sprinklers, water early in the day so the foliage has time to dry off before evening, to minimize disease problems. Keep the soil moist but not saturated.
- Do NOT cut plants back after harvest, allow them to fern and grow as long as they can before frost. They will become quite large. They need the green foliage to make food for themselves to make strong plants next year.
- Have your soil tested for fertilizer recommendations. Fertilize after harvest and in late summer.
- Monitor for pests and diseases. Check with your local Cooperative Extension Service for pest controls recommended for your area.
- In late fall cut tops to ground level when they have turned brown. In cooler climates mulch the ground with evergreen branches or straw after the ground freezes for extra protection. Remove this winter mulch in early spring.
Harvesting and Preserving Tips
- Do NOT harvest asparagus the first year. Allow the plants to grow and make food to store in the roots for stronger plants the following year. When plants are two years old you can harvest them for a short period. In the third year you can harvest for four weeks.
- Harvest when new spears emerge in spring. Harvest when spears are about ½ inch wide. On average spears should be 6-8 inches tall.
- Using a sharp, clean knife, cut young spears at ground level and set in water with the cut side down until you are ready to store the spears. Some gardeners prefer to snap the stems, but this can cause damaged tissue which can result in disease issues.
- Harvest frequently before spears start to leaf out.
- Do not harvest spears less than ¼ inch in diameter.
- Prepare as soon as possible as fresh asparagus is best.
- Asparagus also freezes well for later use. Sort the spears by thickness and “blanch” smaller ones 1 ½ minutes, medium for 2 minutes and thickest for 3 minutes. To do this, drop the spears into boiling water for the recommended time, then plunge into cold water to stop the cooking, drain and store in freezer bags or vacuum bags.
Common Disease Problems
Asparagus Rust: This fungus disease causes rust colored spores on the stems and foliage of asparagus. The plants can appear to have prematurely matured. The disease is favored by prolonged rainy weather, and attacks the ferns after harvest and is spread by wind and rain. Severe attacks can result in a decline in crown vigor. Burpee Recommends: To avoid rust, plant resistant varieties, such as Mary Washington. Avoid getting water on the foliage when watering. Remove severely affected foliage. Contact your Cooperative Extension Service for preventative fungicide recommendations.
Cercospora Needle Blight: A fungal disease that affects ferns in mid-season, causing them to die prematurely. Affected foliage will have small tan to gray oval shaped spots with reddish edges. The disease spreads in prolonged rainy weather. Burpee Recommends: Contact your Cooperative Extension Service for fungicide recommendations.
Crown Rot: Caused by a soil borne fungus that rots the stems at the soil line. It interferes with the plants’ ability to take up nutrients and water and plants will decline and die. Burpee Recommends: Do not plant asparagus in the same area for at least eight years.
Fusarium Wilt: A soil borne disease that causes the roots to rot. The infection can enter the plant through wounds caused by cultivation, insects or harvesting. The spears will shrivel and ferns turn yellow and wilt. There is no cure for the disease. Burpee Recommends: Some varieties are tolerant to the disease. Do not plant asparagus where this problem has occurred.
Purple Spot: This fungus causes tan to brown lesions to develop on spears. They may coalesce and cause defoliation. Burpee Recommends: Contact your Cooperative Extension Service for fungicide recommendations.
Common Pest and Cultural Problems
Asparagus Aphids: These are powdery gray-green colored sucking insects that inject toxins into the plant as they feed on the undersides of leaves causing the plant to be stunted and have abnormal growth. Burpee Recommends: You can wash them off with a strong spray, or use an insecticidal soap.
Asparagus Beetle (Common): The common asparagus beetle adults are ¼ inch long with black wings with red margins and three large yellow squarish spots. The larvae are blue-gray with black heads. They feed on the ferns and weaken the plants. The beetles are active, but shy, and may drop to the ground or to lower leaves when disturbed, and they make a squeaking noise when they are caught. They overwinter as adults and congregate on the young shoots when they emerge in spring. They lay rows of three to eight black eggs at the ends of the spears and on the foliage. The eggs hatch in a week and the young larvae feed on the leaf tips to feed. After two weeks they drop to the soil and change into adults. There are several generations throughout the growing season. The larvae excrete a black fluid on the tips, and adult feeding can damage the buds and stems of the young shoots causing them to be woody and crooked. Burpee Recommends: To control, hand pick, or knock the larvae to the ground by brushing the plants with a broom. Contact your Cooperative Extension Service for pesticide recommendations.
Browning Foliage: This can result from drought stress, particularly in mid-summer. Burpee Recommends: A drip irrigation watering system and mulch can help control drought stress.
Cutworms: These can feed on the spear tips and sides. The brown to pale yellow larva can be 2 inches long and lives in the soil. The adults are moths that lay their eggs in weeds. Burpee Recommends: Place a paper cup collar (use a coffee cut with the bottom cut out) around the base of the plant. They are usually mostly a problem with young seedlings. You can also control by handpicking and controlling weeds, where they lay their eggs.
Twelve Spotted Asparagus Beetle: This beetle is reddish orange with twelve black spots on its back. Overwintering adults cause damage by feeding on the tender spring shoots. The eggs are yellowish to light green and are attached by their sides to the leaves. The young larvae feed on the berries of the female plant. Burpee Recommends: Hand pick and contact your local Cooperative Extension Service for pesticide recommendations.
Asparagus FAQs
Do I need male and female plants to get asparagus? No, we eat the leaf buds of asparagus, there is no need for pollination or fruiting. Some varieties are mostly male, and these tend to be stronger varieties. The female plants are not as strong and produce weedy seedlings, but the spears tend to be larger.
Are the red berries edible? Can I tell what sex a plant will be from the red berry? No and no.
How can I get that white asparagus I see in gourmet stores? White asparagus is not a specific variety of asparagus; it is regular asparagus that has been blanched as it grows. Keep the growing green spear from the sunlight and it will turn white.
How many plants do I need for a family of two? For a family of four? We recommend 25 roots for a family of two, 50 for a family of four.
I planted my asparagus this spring and want to move them to a new location, can I do that? Moving asparagus once planted is not recommended. The roots planted in spring are already one year old and need to become established before you can begin harvesting. Moving them will delay harvest for another year, and be disruptive to their development. If you must move them move them in fall after the ferns die back.