How Do I Grow Asparagus?
Though I have been a gardener for decades, I did not always grow asparagus because I was hesitant to commit a garden bed to a long-lived perennial crop, but in time I realized I was missing out on one of nature’s greatest gifts.
Home-grown asparagus is unsurpassed in flavor and sweetness, and it’s downright beautiful too. The foliage is tall and ferny, making a perfect backdrop to your other plants — especially if you have female asparagus plants, which produce little red berries that hang like ornaments. Asparagus can be roasted, steamed, sauteed or blanched, and you can add garlic, lemon or butter to help bring out the flavor. If you want to grow asparagus in your garden, here’s everything you need to know.
You can also download my How Do I Grow Asparagus? one-sheet and keep the free resource handy for your reference.
Though attractive, those red berries on female asparagus plants pull energy away from productivity. To increase the number of spears an asparagus patch produces, plant breeders have developed varieties that are exclusively male and, therefore, higher yielding.
One of the most unique things about asparagus is how long it lasts. It’s not uncommon for an asparagus patch to continue to put up tasty spears 20 years after it was first planted. That’s a great return on investment.
Asparagus can be raised from seed, but the way most gardeners start asparagus is from crowns, which are 1-year-old roots with buds. They usually come in packs of 25, and 25 crowns will produce 20 pounds of spears annually once they are established.
How to Start Asparagus from Seed
If you do decide to go the seed route, use pathogen-free seed from a trusted source. Asparagus seed can remain viable for three years if stored in ideal conditions, but for the best germination rate, use it the first year.
Asparagus seeds should be started 12 to 14 weeks before the last frost date of spring. For faster germination, soak the seeds in water for a few hours before sowing. In a clean seed-starting medium, sow seeds a half-inch to three-quarters-inch deep. If the temperature of the seed-starting medium stays between 60° and 85° the seeds will germinate in eight to 12 days.
Keep the seedlings under a grow light from the moment they sprout. Otherwise, they will stretch out in search of sun. Ten days before you plan to plant out the asparagus seedlings, begin to harden them off to get them accustomed to outdoor conditions. On the first day, put them out in the sun for just an hour. On the second day, increase the time in the sun to two hours. Add an hour each day, and by the end of the hardening off period, the plants should be ready to be transplanted out in full sun.
Where, When & How to Plant Asparagus
Because asparagus is a perennial that can remain productive for 20 years or more, it’s important to choose a spot for it carefully. The plants will produce tall fern-like foliage as the year progresses, so site them in a location that gets full sun and where the growth won’t shade out other plants. The north side of the garden or a dedicated space where they can grow undisturbed for years is ideal.
The soil pH should be neutral — somewhere between 6.5 and 7.5. When the pH is in the correct range, the plants will be better able to take up nutrients from the soil. A soil test by your local cooperative extension will let you know the pH level and how to adjust it, if necessary. A soil test will also let you know if any micronutrient deficiencies exist.
Refraining from planting seedlings or crowns outdoors until the soil temperature has reached 50°. An inexpensive soil thermometer can give you a quick reading.
Plant crowns in early spring unless you live in a very warm region, where crowns should be planted from fall through winter.
In all cases, plant crowns in furrows that are 5 to 8 inches deep, bud-side up and with the roots spread out. Planting shallow is safest in heavy soil. Plant deeper in colder climates. Allow 8 to 14 inches between crowns and 3 to 6 feet between rows.
Don’t backfill furrows to the soil surface immediately after planting. Instead, cover with just 2 to 3 inches of soil at planting time and then gradually add soil to fill the furrow as the spears continue to lengthen.
Garden asparagus is all the same species, Asparagus officinalis. The many different varieties of asparagus offer tolerance to either cool or warm climates and varying degrees of resistance to diseases. Asparagus stalks may be green, purple, or green with purple tips.
It’s chlorophyll that makes most asparagus green and the pigment anthocyanin that makes the tips or whole spears of certain varieties purple. “White asparagus,” which is popular in many Asian and European countries, is actually green asparagus that was covered in mulch or soil. Because the spears were denied sunlight, they did not green up and are also more tender.
Erasmus is the first all-male purple asparagus. The flavor is sweeter than the average asparagus and the texture is more tender. It’s designed for a mid-early harvest and grows in zones 3 to 10.
Guelph Millenium is an all-male variety developed at the University of Guelph in Ontario. It’s cold tolerant and very productive, and the solid green spears are tasty. It’s an RHS Award of Garden Merit recipient and suited for growing in Canada and the northern United States.
Jersey Giant is part of the Jersey series of all-male asparagus varieties. It has medium to large green spears and attractive purplish bracts. This variety is cold-tolerant and resistant to rust disease.
Jersey Knight has large green spears and uniform size. It grows well in most climates and is highly resistant to rust. It’s more tolerant to fusarium than other varieties.
Jersey Supreme is high yielding with slim green spears. A good variety for cool and warm regions, it’s also resistant to rust.
Mary Washington Improved is an open-pollinated green variety that produces more spears and tighter tips than its predecessor but with the same outstanding flavor. It’s can’t tolerate high heat, so cut spears before the temperature goes above 70°.
Pacific Purple is a British asparagus that is flavorful and high yielding. It has extra thick, deep-purple spears If growing from seed, plan on waiting 750 days for the first harvest. Pacific Purple is rated for zones 3 to 9.
Purple Passion has large-diameter purple spears that are sweeter and more tender than green varieties. It emerges later than green varieties, which can be an advantage in avoiding early frost damage. The purple fades when the spears are cooked.
Spartacus is an all-male hybrid variety that is green with purple-tinged tips and more productive than Jersey varieties. Spears are consistently long — more than 9 inches. This variety is adapted for both cold winters and warm summers
Even and consistent watering is important for asparagus throughout the growing season, but especially during the initial planting phase. Avoid overhead watering, as getting the foliage wet can invite pathogens. Apply water at the ground level only. Applying mulch will help retain moisture between waterings and will create a barrier between the foliage and soilborne pathogens.
Asparagus is a really great candidate for drip irrigation because both the irrigation tubing and the plants can remain in place for many years. Drip irrigation will keep the soil consistently moist during the growing season.
Asparagus appreciates a steady supply of nutrients from well-rotted manure, compost, fish emulsion or a balanced organic fertilizer. Applying organic mulch will also provide nutrients to the soil.
As perennials, asparagus plants will be growing and producing for years. Make sure key resources are available throughout their active growing time to ensure productive plants from season to season.
Asparagus Pests & Diseases
Asparagus pest and disease issues can be overcome by choosing resistant varieties and employing organic controls. Installing floating row cover over plants can stop many insect pests from ever laying their eggs. Row cover is a physical barrier that will have to be removed once the plants get a bit taller, but in the time that it is in place, it makes a big difference. Controlling weeds, refraining from overhead watering, and harvesting with sanitized tools are all ways to reduce occurrences of pest problems or diseases.
Asparagus aphids cause deformity and stunted growth, damaging the spear tips with their feeding. Aphids are sucking insects that are vectors for plant diseases. As they feed on plant leaves they excrete honeydew, which attracts ants and other insects. They are easily controlled by knocking them off plants with a sharp stream of water or insecticidal soap.
Asparagus beetles can be found in both common and spotted varieties. The common asparagus beetle is the greater threat because it lays its eggs and feeds on spears, causing them to become deformed and damaged. The spotted asparagus beetle also feeds on spears, but lays its eggs on fern foliage.
Cutworms cause bent or crooked stems. They are caterpillars that feed on roots and stems. The larvae overwinter as eggs or larvae, so row cover won’t resolve a cutworm issue. Staying on top of weeding can reduce cutworm populations.
Japanese beetles can cause heavy foliage damage, which results in a lack of photosynthesis. That leads to lower plant vigor and reduced productivity. An adult Japanese beetle is about 3/8th of an inch long. Its wing covers appear metallic — like copper with green fluorescence — while its abdomen has five tufts of white hair on each side. A Japanese beetle larva is a white grub that grows to an inch long. Grubs are found in the soil in a curled position. Grubs can be controlled with Bacillus thuringiensis galleriae (Btg), milky spore and parasitic nematodes, and adults can be organically controlled with Btg and by handpicking. For complete information, read my guide to Japanese Beetle Prevention & Control.
Fusarium is a soilborne or seedborne fungus that causes various symptoms: root rot, crown root, and overall wilting.
Purple spot is a fungus that causes sunken purple lesions on stalks and tan or brown lesions on foliage.
Rust is a fungus that produces orange spore masses on plant stalks.
Your first opportunity to harvest asparagus will happen the second spring after planting crowns. For seed-grown asparagus, it will take an additional year for spears to be ready.
As you make your first harvest, go easy: take no more than two or three spears per plant. In subsequent years, harvest pencil-thick spears when they are about 6 to 8 inches tall. You can continue to harvest as long as spears are more than three-eighths of an inch in diameter. You’ll know it’s time to stop harvesting when most new spears remain small and bud tips start to expand and open. Those remaining ferns will continue to grow, providing energy for the plants below ground.
You can cut or snap the spears off near the soil level, but here’s my advice: take each spear between your thumb and forefinger, and snap it near the base. What ends up in your hand is the best part — that part of the spear you want to eat. The lowest part of the spear is tough and woody, and you’re better off leaving it behind in the garden rather than cutting it off in your kitchen.
Asparagus is best when enjoyed extra fresh from the garden, so plan to serve it on the day of harvest or as soon as possible.
At the end of each growing season, cut back the ferny growth that will become brown and stiff by fall. You can leave the cut growth in place as mulch, and it’s a good time to check the soil pH and add compost or other soil amendments. In all cases, cover the bare soil with straw or shredded leaf mulch once you’ve completed maintenance.
What are your secrets to growing asparagus successfully? Let us know in the comments below.
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Links & Resources
Some product links in this guide are affiliate links. See full disclosure below.
Episode 094: How to Start and Care for Seedlings Indoors: My Steps for Success
Episode 99: Understanding Crop Rotation: The Basics and Beyond, with Jack Algiere
Episode 195: Identifying and Controlling Garden Pests Organically
Episode 204: Hardening Off and Setting Plants Up for Success in Spring
joegardener blog: Powdery Mildew Prevention & Control
joegardener blog: How Do I Grow Artichokes?
joegardener blog: How Do I Grow Beets?
joegardener blog: How Do I Grow Broccoli?
joegardener blog: How Do I Grow Brussels Sprouts?
joegardener blog: How Do I Grow Cabbage?
joegardener blog: How Do I Grow Cauliflower?
joegardener blog: How Do I Grow Herbs?
joegardener blog: How Do I Grow Melons?
joegardener blog: How Do I Grow Onions?
joegardener blog: How Do I Grow Peas?
joegardener blog: How Do I Grow Peppers?
joegardener blog: How Do I Grow Spinach?
joegardener blog: How Do I Grow Strawberries?
joegardener blog: How Do I Grow Summer Squash?
joegardener blog: How Do I Grow Swiss Chard?
joegardener blog: How Do I Grow Tomatoes?
joegardener blog: How Do I Grow Winter Squash?
joegardener blog: Japanese Beetle Prevention & Control
How Do I Grow Asparagus? one-sheet
joegardener Online Gardening Academy™: Popular courses on gardening fundamentals; managing pests, diseases & weeds; seed starting and more.
joegardener Online Gardening Academy Beginning Gardener Fundamentals: Essential principles to know to create a thriving garden.
joegardener Online Gardening Academy Master Seed Starting: Everything you need to know to start your own plants from seed — indoors and out.
joegardener Online Gardening Academy Growing Epic Tomatoes: Learn how to grow epic tomatoes with Joe Lamp’l and Craig LeHoullier.
joegardener Online Gardening Academy Master Pests, Diseases & Weeds: Learn the proactive steps to take to manage pests, diseases and weeds for a more successful garden with a lot less frustration. Just $47 for lifetime access!
joegardener Online Gardening Academy Perfect Soil Recipe Master Class: Learn how to create the perfect soil environment for thriving plants.
Disclosure: Some product links in this guide are affiliate links, which means we get a commission if you purchase. However, none of the prices of these resources have been increased to compensate us, and compensation is not an influencing factor on their inclusion here. The selection of all items featured in this post and podcast were based solely on merit and in no way influenced by any affiliate or financial incentive, or contractual relationship. At the time of this writing, Joe Lamp’l has professional relationships with the following companies who may have products included in this post and podcast: Rain Bird, Corona Tools, Milorganite, Soil3, Greenhouse Megastore, Territorial Seed Company, and TerraThrive. These companies are either Brand Partners of joegardener.com and/or advertise on our website. However, we receive no additional compensation from the sales or promotion of their product through this guide. The inclusion of any products mentioned within this post is entirely independent and exclusive of any relationship.