A quick guide to asparagus

• An asparagus plant can last 15 years. Choose its spot in the garden carefully.
• You can start asparagus from seed or from one-year-old roots, called crowns.
• Crowns grow vertically and horizontally. Planting at the right depth is important.
• Good soil moisture is important at planting for good root and fern growth.
• Begin harvest two years after planting crowns, and three years after planting seeds.
• Harvest spears until June 30, then allow the large feathery ferns to develop.

How asparagus grows

Asparagus is a unique crop and one of the few perennial vegetables grown in home gardens, alongside horseradish and rhubarb. The edible parts we harvest are called spears, which are technically the stems of the plants.

These spears emerge from underground buds at the base of the root system, known as "crowns." If left to grow, spears develop leaves and transform into feathery structures called ferns. The harvest season lasts only 6-8 weeks (early May to late June) because the plants need time for their ferns to grow and build energy for next year's crop.

The ferns create and store energy in the underground portion of the plant, which produces the following year's spears. This is why caring for the ferns after harvest is crucial for ensuring good future harvests.

Soil pH and fertility for asparagus

Asparagus thrives in well-drained soils with a pH between 6.5 and 7.0. It cannot tolerate extremely acidic soils but can grow in heavy, medium, or sandy soils as long as they drain well and don't pool water after rains.

Before planting, have your soil tested to determine nutrient levels. Add recommended fertilizer based on soil test results. It's best to add part of the fertilizer in fall or spring before planting, with about half of the phosphorus and potassium added at planting time. Add nitrogen after planting once crowns begin growing.

Without a soil test, use 1 to 1.5 pounds of 10-10-10 fertilizer per 100 square feet before planting. Once established, test soil every three years and fertilize in early spring before spear emergence or after harvest in late June/early July.

Important: If soil tests show high phosphorus levels, use low-phosphorus fertilizers (32-3-10, 27-3-3, or 25-3-12) or non-phosphorus options (30-0-10 or 24-0-15) at half a pound per 100 square feet. Avoid "Weed and Feed" products as herbicides can kill vegetable plants.

Selecting plants

Asparagus plants are dioecious, meaning there are separate male and female plants. Both produce edible spears, but they have different characteristics:

Female Plants:

• Produce red, inedible berries in summer
• Grow larger spears
• Can produce undesirable weedy seedlings

Male Plants:

• Produce more numerous, smaller, uniform spears
• Don't waste energy on seed production
• Tend to live longer and be more productive

Recommended Varieties for Cold Climates:

• Millennium: Newer variety, very vigorous and high-yielding
• Jersey Series: Jersey Giant, Jersey Knight, Jersey Supreme - popular and high-yielding but can be damaged at -30°F without snow cover
• Mary Washington: Open-pollinated, lower yielding but very cold-hardy
• Viking KB-3: Open-pollinated variety
• Purple Passion: Purple, open-pollinated variety

Choose a good location

Since asparagus plantings can last 15 years or more, location selection is crucial. Choose a site that meets these requirements:

• Sunlight: Full sun exposure for best growth
• Drainage: Well-drained soil that doesn't stay waterlogged
• Moisture retention: Soil that holds moisture well but drains excess water
• Frost protection: Avoid low-lying areas prone to late spring frosts that can kill emerged spears
• Root space: Deep soil for extensive root systems - avoid shallow or water-saturated soils
• Garden placement: If part of a larger vegetable garden, place at the north end so tall ferns don't shade other crops

How to plant crowns

Following correct planting methods is essential for this long-lived perennial crop. Plant asparagus crowns between early May and early June.

Preparation:

• Order crowns for delivery close to planting time
• Refrigerate crowns until planting to maintain freshness
• Prepare soil as described in previous sections

Planting Process:

1. Dig trenches: Create 6-12 inch deep furrows (6-8 inches for clay soil, 10-12 inches for sandy soil)
2. Space properly: Make trenches as long as needed (1 foot per crown) with 3+ feet between multiple rows
3. Position crowns: Place crowns "head-to-toe" (bud-to-root tip) with buds spaced 12 inches apart
4. Add fertilizer: Apply phosphorus and potassium fertilizer to furrows
5. Cover partially: Cover crowns with 2-3 inches of removed soil
6. Water immediately: Don't let crowns dry out - water right after planting

Post-Planting Care:

Spears will emerge within 2-3 weeks. Once spears are sturdy and several inches tall, gradually backfill more soil into furrows as ferns grow, being careful not to break brittle spears with large soil clods.

Note: Ignore outdated advice about spreading roots like an octopus - this is unnecessary.

Growing from seed

While asparagus is typically planted as crowns, gardeners can start from seed following these steps:

Nursery Bed Setup:

• Choose a level area with sandy soil as a nursery bed
• Young plants will grow here for their first year

Planting Process:

1. Plant seeds in spring, 1 inch deep, 2-3 inches apart
2. Space rows 1 foot apart
3. Seeds take up to 3 weeks to germinate
4. Keep nursery bed completely weed-free - seedlings cannot compete with weeds
5. Mulch with 4-6 inches of straw in late October for winter protection

Transplanting:

In early April of the following year, before plants start growing, carefully dig up crowns with as much root system as possible and transplant to permanent location using the crown planting method.

How to keep asparagus healthy and productive

Watering Requirements:

Consistent soil moisture is crucial for healthy root and fern growth. Asparagus patches need at least 1 inch of water weekly. Even though ferns rarely show obvious drought stress, they require consistent moisture to stay healthy for next year's production.

• Water sandy soils more frequently in absence of rain
• Heavy clay soils need less frequent watering
• Mulched soils retain more moisture
• One inch of water penetrates 10 inches in sandy soil, 6 inches in clay

Weed Management:

Weeds compete with asparagus for nutrients, water, and light, reducing spear yields. Multiple management strategies work best:

• Hand removal: Most effective for small beds and perennial weeds like Canada thistle
• Shallow cultivation: Only before spring emergence or after harvest (less than 2 inches deep)
• Cover crops: Plant perennial groundcover between rows in larger patches
• Mulching: Use straw or leaves, but push away from rows in early spring
• Flame weeding: Effective for small seedlings using propane weeders

Timing is critical: Never cultivate during harvest season when new spears emerge daily.

New crown plantings

Newly planted crowns have very small root systems, making good weed management critical for establishment. Just a few weeds around each plant can cause slow growth and reduced future spear production.

Focus intensive weed control efforts during the first year after planting. Hand weeding is often the most effective approach for new plantings, as cultivation can damage the developing root system.

Using herbicides in garden-scale asparagus patches

Home gardeners can use glyphosate (Roundup) in asparagus patches at specific times:

• Early spring: Before spears emerge
• Post-harvest: After all spears are harvested in late June when no ferns are present

Important restrictions:

• Never use herbicides when spears or ferns are present
• Always read and follow label directions carefully
• Ensure the herbicide is approved for use in asparagus
• Observe required days between application and harvest

Caution: Pesticide information is for educational purposes only. Always follow container label instructions, which constitute the legal requirements for use.

Harvest

Harvest Timeline:

• Year 1 (after planting crowns): No harvest - allow all spears to become ferns
• Year 2: Harvest for 2 weeks only when spears are 6-8 inches long, then let remaining spears become ferns
• Year 3 and beyond: Harvest until July 1st

Some gardeners prefer to skip harvesting entirely in year 2, waiting until year 3 to begin harvesting for maximum plant strength.

Harvest Technique:

• Cut or snap spears when 6-8 inches tall
• Harvest every 1-2 days during peak season
• Stop harvesting by July 1st to allow fern development
• Never harvest all spears - plants need some to become ferns

During peak season, spears can grow up to 2 inches per day, requiring frequent harvesting for best quality and continued production.

Storage

Fresh asparagus is best enjoyed immediately after picking, but proper storage extends its usability:

• Fresh storage: Keep up to one week in refrigerator in plastic bag in crisper drawer
• Freezing: Asparagus can be frozen for longer-term storage
• Canning: Must be processed in a pressure canner for safety

For best flavor and texture, consume asparagus as soon after harvest as possible.

Managing pests, diseases, and disorders

Common Pests:

• Cutworms: Cut spears off at the base
• Asparagus beetles: Feed on spears causing browning, scarring, and shepherd's crook bending
• Aphids: Occasionally colonize ferns in large numbers

Common Diseases:

• Asparagus rust: Yellow and rusty orange spots on stems after harvest
• Purple spot: Sunken purple spots on spears, tan spots with purple borders on mature stems
• Crown rot: Poor growth, yellowing leaves, brown and decayed crowns when cut open

Environmental Issues:

• Herbicide drift: Causes spears to hook, curl, and bend
• Frost damage: Freezing temperatures after emergence cause spear bending and curling

Proper cultural practices including good drainage, appropriate spacing, and avoiding over-harvesting help prevent many disease issues. For accurate diagnosis of problems, contact your local extension service or master gardener program.