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How to Grow Asparagus

Green young asparagus sprouts in the garden

Asparagus harvestAsparagus is the first sign of Spring in many vegetable gardens.

Stalks or spears begin to break the soil in early spring as soon as the soil temperature reaches 50°F (10°C).

Asparagus is a perennial vegetable that requires three to four years to become established and productive. Once established, an asparagus plant can produce spears for 15 to 20 years or more.

Asparagus Planting Time

  • You can grow asparagus from seeds, crowns (roots), or transplants.
  • Start seed indoors 12 to 14 weeks before the last frost.
  • Transplant seedlings or plants into the garden after the last frost.
  • Plant asparagus seeds or crowns in the garden in early spring as soon as the soil is workable. The soil temperature should be 50°F (10°C) or warmer.
  • Allow asparagus 3 years to establish its roots before you begin harvesting.
Asparagus growing
Grow asparagus in raised beds if the native soil is poor.

Where to Grow Asparagus

  • Asparagus is a perennial. Plant asparagus in a spot where plants can grow undisturbed and productive for 15 to 20 years.
  • Plant asparagus in full sun where it gets plenty of air circulation; this will help prevent disease. Asparagus can tolerate partial shade.
  • Plant asparagus out of prevailing winds; wind can damage or break stalks.
  • Asparagus grows best in loose, compost-rich well-drained soil. Sandy loam is good soil for growing asparagus.
  • Add 3 to 4 inches (7-10cm) of aged compost to the planting bed and turn it under to 12 inches (30cm) deep or more before planting asparagus.
  • Plant in raised beds if your native soil is poor or constantly wet.
  • A soil pH between 6.5 and 7.5 is best for growing asparagus.

Starting Asparagus from Seed Indoors

  • Asparagus plants grown from seed are less susceptible to transplant shock than those started from crowns. Also, an asparagus plant started from seed will be more productive over the course of its life than a plant started from a crown.
  • Sow seed 8 to 10 weeks before you plan to set transplants in the garden.
  • Soak seed in compost tea for 5 to 10 minutes before planting; this will help reduce disease problems.
  • Sow seed 1½ inch (3.8cm) deep in a seed-starting mix or light potting soil. Sow seeds in individual containers.
  • Seeds will germinate in 7 to 21 days at 75°F (24°C).
  • Place seedlings in a cold frame, plastic tunnel, or greenhouse to grow on until outdoor temperatures are warm enough for transplanting. The optimal growing temperature is 60° to 70°F (15-21°C).
  • Male plants produce more spears than female plants. You can cull out female plants by looking at the flowers. Female flowers have three-lobed pistils; male flowers are larger and longer than female flowers.

 Starting Asparagus from Seed Outdoors

  • Start asparagus outdoors from seed in a protected nursery bed or under a portable plastic tunnel or cold frame.
  • Sow 2 seeds per inch (2.5cm); space rows 18 inches (45cm) apart.
  • When seedlings are 3 inches (7.6cm) tall, thin plants to 4 inches (10cm) apart.
  • At the end of the summer, transplant male plants to a permanent spot. You can keep female plants to grow on, but they will produce fewer spears than male plants.

Growing Asparagus from Crowns

  • Asparagus can be grown from roots (called crowns). Crowns are sold at garden centers in late winter and spring and online by seed companies. Crowns are the roots of plants started by a seed grower.
  • You can purchase one, two, or three-year-old crowns. One-year-old crowns are less susceptible to transplant shock.
  • A viable crown will be fresh, firm, and healthy-looking. Avoid crowns that look dry or shriveled.
  • Store crowns until planting time in moist peat moss or sphagnum moss.
Asparagus growing bed
Continue to mound up soil over the spears as they grow up so that plants are growing on 4-inch tall or higher ridges or rows.

Planting Asparagus Crowns Outdoors

  • Before planting soak crowns for 10 to 15 minutes in compost tea.
  • Plant crowns in beds already prepared with aged compost or commercial organic planting mix.
  • Dig a trench 6 to 8 inches (15-20cm) deep and 12 inches (30cm) wide. Space trenches 3 to 4 feet (.9-1.2m) apart.
  • Create a 2-inch-high (5cm) furrow or mound down the center of the trench.
  • Set crowns atop the mound; drape the crown’s spider-like roots over the edges of the mound. Set crowns 18 to 24 inches (45-61cm) apart.
  • Cover crowns with 2 inches of soil. Spears will begin to grow in a few weeks.
  • As the spears grow from the crown, cover them again with 2 inches (5cm) of soil. Repeat this process until you gradually fill in the trench.
  • Continue to mound up soil over the spears as they grow up so that plants are growing on 4-inch (10cm) tall or higher ridges or rows.
  • Plant between 30 and 40 plants for each person in the household.

More tips at Asparagus Growing.

More tips on starting asparagus plants: Asparagus Plant Starting Tips.

Watering Asparagus

  • Keep asparagus planting beds evenly moist but not wet throughout the growing season.
  • Mature plants can survive without extra watering, but the stalks may become stringy and woody.

Feeding Asparagus

  • Add two inches of aged compost to planting beds every spring or sprinkle a high phosphorus and potassium fertilizer, such as 5-10-10, down rows before spears appear in spring. Do this again at the end of the harvest.
Asparagus in loamy soil
Keep asparagus beds well weeded. Competition from weeds will lower the yield of asparagus.

Caring for Asparagus

  • Mound 1 to 2 inches (2.5-5cm) of aged compost or commercial organic planting mix over asparagus established crowns every spring. Aged compost has all the nutrients asparagus plants need. Plants will easily grow up through the added soil.
  • Keep asparagus beds well weeded. Competition from weeds will lower the yield of asparagus.
  • To grow white asparagus spears, blanch the shoots by mounding soil up around the spears as they grow.
  • Erect windbreaks if there is a prevailing breeze; blowing soil can damage spears.
  • When plants become dry and brittle in autumn, cut plants back to 1 inch above the soil. Add aged compost or commercial organic planting mix over plants.
  • If a frost or freeze is forecast, protect spears and crowns by covering them with several inches of straw or chopped leaves. Unprotected spears hit by a freeze will turn brown and soft or they may die.

Companion Plants for Asparagus

Plant tomatoes, parsley, and basil near asparagus. Avoid planting root vegetables near asparagus.

Asparagus Pests

  • Asparagus beetles may attack asparagus, especially in commercial asparagus growing districts.
  • Asparagus beetles and larvae chew spear in spring and feed on fronds in summer.
  • Pick off and destroy asparagus beetles or spray with insecticidal soap or pyrethrins.

Asparagus Diseases

  • Asparagus is generally disease-free.
  • Fungal diseases such as rust and fusarium wilt can attack asparagus. Spray-mist plants with compost tea to prevent fungal diseases.
  • Treat seed to prevent disease before planting; soak the seed in a one part bleach to nine parts water solution for two minutes then rinse the seed.
  • Plant disease-resistant cultivars.

More about asparagus pests and diseases: Asparagus Growing Problem Troubleshooting.

Harvest asparagus
Snap spears off at soil level with your fingers at or just below ground level. If you use a knife, be careful not to injure nearby crowns.

Harvesting Asparagus

  • Begin the asparagus harvest when plants are three years old and fully developed.
  • Pick spears for only two weeks the third year (which is the first harvest); let plants continue to establish themselves; over-harvesting can weaken plants and cause future harvests to be small.
  • The fourth year after planting, extend the harvest to 4 weeks.
  • Every year after the fourth year, you can extend the harvest by a week or two until you are harvesting up to 8 weeks.
  • Cut spears when they are 6 to 10 inches (15-25cm) tall and at least the diameter of a pencil. Tips should be firm and closed.
  • Snap spears off at soil level with your fingers at or just below ground level. If you use a knife, be careful not to injure nearby crowns.
  • When spear bracts begin to feather out, it is too late to eat them.
  • If temperatures approach 90°F (32°C) at harvest time, harvest daily; heat can cause bracts to open prematurely.

More tips on growing asparagus: Asparagus Growing and Care Calendar.

Asparagus plant ferns
Just after the middle of summer (in late July) cut the ferny plants down to the ground. New spears will grow for a second harvest.

How to Extend the Harvest: Harvest Twice a Year

  • To extend the harvest, plant twice as many plants.
  • Harvest half of the plants as usual from spring to early summer.
  • Let the other plants/spears grow on; they will grow on to become tall ferny plants.
  • Just after the middle of summer (in late July) cut the ferny plants down to the ground.
  • New spears will emerge in autumn; harvest these spears like you would spring spears.

Storing and Preserving Asparagus

  • Asparagus is best used fresh.
  • Asparagus will keep for up to 1 week in the refrigerator. Place spear upright in an inch or so of water and refrigerate.
  • Freeze asparagus after blanching.

More on How to Harvest and Store Asparagus.

Asparagus sprouts
Green young asparagus sprouts in the garden

Asparagus Varieties to Grow

  • ‘Jersey Knight’ (male): heavy producer.
  • ‘Jersey Giant’ (male): grows well in the East and Midwest.
  • ‘Larac’ (male/female): pale, nearly white, French cultivar.
  • ‘Mary Washington’ (female): heirloom traditional variety.
  • ‘Millennium F1’ (male): grows well in very cold northern gardens.
  • ‘Purple Passion (male/female): colorful, tender.
  • ‘UC 157’ (male): a good choice for West Coast weather.
  • ‘Viking’ (male): excellent for cold climates, tender, tasty.

About Asparagus

  • Asparagus is a hardy perennial that produces tender, fleshy, green stems or “spears” with bud-forming caps.
  • Grown to maturity the asparagus has a fernlike, feathery foliage.
  • The asparagus is long-lived staying in the garden for 15 years or longer.
  • Botanical name: Asparagus officinalis
  • Origin: Mediterranean

More tips: Asparagus Planting Tips.

Grow 80 vegetables and herbs: THE KITCHEN GARDEN GROWERS’ GUIDE

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11 Comments

  1. I planted asparagus for the first time ever this afternoon. I follow the square foot gardening methods and dug a hole in each 12″ square instead of trenches. The problem is that the example pictures that I was using had roots that were just a few inches long. My roots were at least 12″ long and could not be spread out in the hole. Making what I believe now to be a poor decision, I wrapped the roots around the crown in the hole thinking the roots would work their way around. Did I make a grave mistake and how will it affect my production?

    • Asparagus roots are best spread out from the crown. Dig the hole wide and deep enough for the crowns you are planting. With mature roots, the hole should be as wide as 12 inches across. Mound up soil in the center of the hole and set the crown atop the mound and then spread the root out fan-like running away from the crown. This is the optimal way to get your asparagus roots growing. If you planted in the past month, it is not too late to uncover the crowns and replant. Asparagus will grow on for 15 years or more so it is a good investment in time to re-plant if you are in doubt.

  2. About 3 years ago I planted asparagus in a raised bed and the soil was about 6 inches from the top of the five foot deep raised bed. Now the soil has sunk way down and it is only between 6 inches and a foot from the bottom of the bed. How can I once again have soil almost to the top of the bed without digging up my plants? How much soil can I add at once and how often can I add soil or it hopeless to have my plants once again near the top of my raised bed? Any help or suggestions would be appreciated. I am in my 80`s and would like to fix the problem. Thank you.

    • As they say: Slow and steady wins the race. Each year when you cut down your asparagus in autumn add two inches of aged compost or commercial organic planting mix across the planting bed. You can add more soil in spring, but the result may be blanched spears, that is white spears rather than green spears. Blanched spears will be milder flavored. You can return the bed to its original depth over a period of a couple of years without removing and replanting the asparagus crowns.

  3. 4 years ago my 25 yr old asparagus bed basically died. I started replacing the bed in the same location with new 2 yr old crowns. I have done that every year now but the crowns don’t grow, or they grow and die. upon inspection this year i found 1 living plant. I have mulched and fertilized to no avail. I am going to get a soil test done soon. Any other thoughts would help.

    • The soil is likely depleted. A soil test will tell you to what degree. If the soil is sandy add a 5-10-10 fertilizer at the rate of 35 pounds per 1,000 square feet. If the soil is heavier, use a 5-10-5 fertilizer at the same rate.

  4. This spring, I planted 25 asparagus crowns, per instructions including trench depth, 18″ spacing and in raised bed garden boxes with moderately-conditioned soil. I back-filled a couple inches at a time every couple weeks or so as spears appeared, using with a ⅓ each part blend of non-manure compost, commercial planting mix and the original moderately conditioned soil. 1 of the plants initially put up a spear which only grew a couple inches then died back, and that plant has never put up another spear. 2 other plants have never put up a spear. As far as I remember, none of the crowns were dry or shriveled. Is there a chance that next year, these 3 crowns will produce normally given good overwintering care and procedures? Or perhaps I can start a few by seed for transplanting into the vacant spaces? (I understand the difficulty and longer time they will take to become productive, but I have not found anyplace to purchase single crowns locally.)

    • Plan to start new asparagus plants by seed. Start the seed indoors between late winter and mid-spring under bright lighting. Soil temperatures for seed germination should be between 70-85 degrees F. (21-29 C.). Soak the seeds for a couple of hours, then plant each seed ½ inch (1 cm). Seedlings will be ready for transplanting in about 10 weeks. As the seedlings are growing, the garden soil will be warming and if the crowns you have in the ground are viable; they will appear before the seedlings are ready for transplanting. If you have both, you will be able to choose the strongest to continue.

  5. Do you have any recommendations for growing asparagus in Zone 10? I’ve started Mary Washington from seed as it stated it could be grown in S. Florida. I’m ready to transplant a bed but I’m not sure if I should plant in full sun or plant in grow bags so I can move them around. I’m concerned our summer heat may kill the plants. Id appreciate any advice you have. Also, are all Mary Washington plants female?

    • Mary Washington is a female asparagus. Asparagus is not a crop commonly grown in South Florida. It is best grown in Zones 3 to 8. That said, check for the closest cooperative extension service office or Master Gardner group to see if they have asparagus growing experience and recommendations for your location. You can also check at a nearby garden center to see if they carry asparagus and which varieties they recommend. All of that said, full sun is the best spot to plant asparagus. If you are starting out, you might want to plant some in beds and some in grow bags and see how the first year goes. The lack of a sufficiently cold winter may cause the plants to perform poorly.

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