Asparagus

 When to Start

Spring: Start indoors 8-12 weeks before the last frost date (Mid February-Early March for Jefferson, GA)

Transplant: For seedlings and bare root crowns, after all danger of frost has passed. (May 1 for Jefferson, GA.)

Direct Sow: After ALL danger of frost has passed. (May 1 for Jefferson, GA.)

How to Grow

Start seeds indoors 8-12 weeks before the last frost date. Soak them overnight. Use sterile, pre-moistened seed starting mix and sow the seeds to a depth of 1/2 inch into cells or seedling pots. Asparagus germinates best with soil temperatures of 65-75 F. A heat mat will help keep soil temperatures consistent. Place the cells or pots under grow lights. Keep in mind they are slow to germinate, sometimes taking a month to sprout. Thin to the strongest seedling per cell or pot. 

When you start indoors, this is also a good time to start preparing both the transplant and permanent beds. Good bed preparation is essential for asparagus. See Care for more details on getting your bed set up.

When the seedlings are 6-10 inches tall with 4-6 stems coming from the crown that have several buds, they are large enough for transplanting. After hardening them off they should be transplanted into a temporary bed.

What is a Temporary Bed

The temporary bed is a sandy location that will make digging up the crowns the following spring easier. The sandy soil helps to minimize any disruption to the roots when digging them up. This temporary spot will allow the crowns to begin developing, as healthy crowns are essential to future harvests. The sandy soil also helps with drainage as asparagus hates wet feet and any standing water could cause crown damage. The seedlings are typically planted closer together than in the permanent as the temporary bed is usually smaller than the permanent one. 

The danger of directly transplanting into the permanent bed is the asparagus crown needs to be planted deeply so that you don’t have spindly spears. When you transplant the seedlings directly into a permanent bed the crown won’t be deep enough. This is why the temporary transplant bed is crucial. 

As it is important not to disturb the roots, you will need to take care when weeding in the transplant bed. Gently pull any weeds from around the asparagus. This is true in the permanent bed too. As the plants grow and fill in, weeds will become less of an issue. 

How To Transplant

When transplanting your seedlings (not the one-year-old crowns), the temporary sandy bed needs to be prepared beforehand. Create a sandy location if you don’t live in an area that has sandy soil. Then dig a hole large enough for the root ball. Carefully remove the seedling from the pot, disturbing the roots as little as possible.

Plant the seedling at the same depth as it was in the seedling pot. Space the plants 12-18 inches apart. Backfill the hole, gently firm the soil, and water the seedling. These seedlings will be dug up and transplanted again in one year.

Direct sowing

Wait until ALL danger of frost has passed for your area. Then in a prepared transplant bed, sow the seeds evenly and thinly 2 inches apart to a depth of 1/2-3/4 inch. Gently firm the soil and water the seeds in. Germination does take time so be patient.

Bare root crown planting

Bare root crown planting is a great way to speed up the wait time before harvest as these are already 1-year-old plants. Asparagus live for 15-20 years and it is important to have good loose soil and the bed in the right location. After ALL danger of frost has passed, in your prepared bed (see Care), dig a trench that is 6-8 inches deep and 12-15 inches wide. Rows should be 2 1/2 to 4 feet apart.

When buying crowns, soak the roots 15-30 minutes in lukewarm water before planting.

When using a transplant bed, dig the one-year-old crowns while they are still dormant in the spring before any growth starts. This is one year after starting from seed. Using a spading fork, dig 6 inches under the plants to gently loosen the soil and lift the crowns. The roots will be long. As they were planted closer together, you will need to carefully separate the roots from neighboring plants before setting the crowns in the permanent location.

The crowns of each plant should be spaced 12-18 inches apart with the bud facing up. Place the roots in the bottom of the trench and spread the roots out to help the roots get well-established. Cover the roots with 2 inches of soil and water well.

It may take 6-8 weeks before you start to see growth. As you see the spears emerge, continue adding soil, leaving the tops exposed until the trench is filled. Keep the soil constantly moist, but not soggy, during this year to allow the crowns to establish. Mulching will greatly help with this, as well as, suppress any weeds while the asparagus gets established.

It is important to allow the spears to fern out this year as ferning out allows the plant to make the food it needs for the following year. Think of it like daffodils. After booming the green foliage makes the food to replenish the bulb so that it can flower again next spring.

Once the trench is full, some gardeners like to taper the bed so that excess water will drain away from the crowns. This is a good idea as the crowns/spears will suffer and may die if left in standing water.

Care

Bed Preparation

Good bed prep is essential for asparagus. Asparagus hates wet feet and loves sandy soil. Soil in asparagus beds should be loosened to a depth of 12-18 inches. In clay soil, you will need to double that depth and make sure that no standing water occurs in the bed, and add lots of organic matter to keep the soil looser. As that is a lot of work, a raised bed might be a better option.

A soil test will be very helpful as this plant likes a soil pH of 6.5-7, slightly acidic to neutral. Some universities state asparagus grows better in more alkaline soil as the Fusarium fungi which generally causes root rot, thrives in more acidic soil. It is good to repeat the soil test every 3 years and follow the guidelines laid out in the report.

As a medium to heavy feeder, mix compost into the soil of the bed when you are loosening the soil and any amendments found in your soil report.

Asparagus doesn’t compete well with weeds, make sure all weeds are removed from the bed before planting. Gently pull any weeds by hand to minimize disturbing the asparagus roots.

Asparagus can live 15-20 years. So you want to plan where they are going to live. They need a bed in full sun. You also want to think about the fact that the ferns grow to 5-6 feet tall. This will create shade. Place the bed where it won’t shade any other full-sun plant.

Watering and Weeding

During the first 2 years asparagus needs 1-2 inches per week to help it get established. Keep the soil moist, but not soggy (wet feet). Bottom water the plants with drip irrigation or soaker hoses to keep the foliage dry. Wet foliage can increase disease risk. Proper spacing will allow for good air circulation and will help decrease the risk of disease. Once the asparagus is established, you may not need to water except it in extreme conditions as the roots when grown in sandy soil can grow 10 feet deep.

A good thick layer of mulch is also recommended to maintain soil moisture and suppress weeds as weed control is very important during the first 1-3 years of life when the crowns are at their most susceptible. Some gardeners use 4-6 inches of mulch as tilling can cut into the crowns and damage them.

Don’t harvest for the first 2 years when starting from bare root crowns and 3 years when starting from seed. Side dress asparagus with compost or well-rotted manure in spring and in the fall (after harvest when you start to harvest). Keep the bed thickly mulched.

After harvest

After harvesting the spears should be allowed to fern out. The mature fern is what makes the food for the next year’s harvest. Side dress with compost to give the plants the boost they need. Keep watering and monitoring for pests and diseases, keeping the plant healthy.

Pruning

After the ferns have turned brown in late fall, cut them down to ground level. In cooler climates, you will need to mulch for extra winter protection. Remove any winter mulch in early spring.

Harvest

Patience is critical to growing a healthy, established crown that will produce bountiful harvests. Don’t harvest for the first 2 years when starting from bare root crowns and 3 years when starting from seed. The plant needs to put all of its energy into creating healthy crowns during the first 3 years of life (from seed to 3 years old).

Asparagus grows from both male and female plants. Both will produce spears. However, the female plants will also produce berries. Some gardeners remove the female plants to increase their harvest, while others remove the berries so that the plant will put more energy into next year’s harvest versus seed production. Only do this if you don’t want to save seeds.

One thing to keep in mind is female plants will produce larger spears, however, their spears will be fewer in number than male plants.

How to Harvest

During the first year of harvest, you will want to harvest lightly for about 2 weeks. During the second year of harvest, you can harvest for about 4 weeks, and then the 3 year, for a full season which is around 6-7 weeks.

When the spears are about 8-10 inches tall and 1/2 inch wide use a sharp clean knife and cut at ground level. It is thought that snapping them can cause tissue damage that leaves the plant open to disease. Although there is some debate about that.

When snapping them, they generally break off above the woody portion so there is little to no trimming of the spears. Immediately, place the spears in water. In warmer weather, you may find that the tip quality is better when harvested at the shorter range.

After harvest allow spears to fern out until they turn brown in the fall. They need the green foliage to make food for themselves for next year. Side dress with compost or well-rotted manure after harvest to help give the plants the energy they need to create next year’s harvest. Continue to water like normal until the plants turn brown in the fall.

One thing to note is if the harvest starts to drop off at any point, this is a sign the crown is beginning to experience stress. It is a good idea to stop harvest if this happens.

Pest Management

Cutworms like to eat off the tips of asparagus spears, as well as, the sides. To control you can hand-pick or use plant collars to protect the spears. You can make your own from aluminum foil or paper or plastic cups. The collars should be 2-3 inches high and pushed firmly into the soil to prevent the cutworms from going over or under. The paper will eventually break down, the others will need to be removed. You could also try trap cropping with sunflowers. You will just need to search for cutworms daily and remove them.

The asparagus beetle can cause damage in both the adult and larval stages. Hand-pick any eggs, which are oval in shape and deposited in rows. The eggs are found on spears, ferns, or flower buds. You can use neem oil according to the packaged directions. To aid in prevention, prune the ferns in the fall after they have turned brown. The beetles like to over-winter in asparagus patches.

You can also make use of companion planting to attract beneficial insects that will eat asparagus beetles. The Tetrastichus asparagi is a green metallic-looking parasitic wasp that is attracted to the asparagus plant. The wasps will paralyze the eggs of the beetles, killing them. Two other beneficial insects to attract are ladybugs and lacewings. They will consume eggs and larvae. See Companion Planting for more information.

Disease

Asparagus rust is a common problem. Plants are prone to rust when the foliage gets wet through watering or prolonged rainy periods. It typically appears after harvest and can lead to decreased crown vigor. Remove debris from the previous year as the disease will move from the foliage from the prior year to the spears of the current year. When the plants are pruned, remove any infected debris (that hasn’t already been removed) and destroy or throw it away, don’t compost.

Rust spreads quickly. It appears as eye-shaped and a creamy orange color in the early part of the season. In the middle of the season, the lesion is a dark red, rusty color. Lesions will appear black in the fall. When seen in fall the foliage should be removed and destroyed or thrown away as it will over winter.

You can work towards prevention by using slightly wider rows (6 feet) and more spacing between the crowns to improve air circulation. Bottom water to keep the foliage dry and sanitize tools used to prevent spread. You can use fungicides for treatment and throughout the summer as a prevention method. Just follow the packaged instructions.

Purple spot is another common problem and can be difficult to identify. It will appear on the spears as purple spots with more severe cases having a gray spot in the center. Cooking the spears usually causes the spots to disappear. When purple spot is in the ferns it is much more serious. Purple spot will be brownish to purplish in color and irregularly shaped and sunken. You might see needles of the ferns drop. Fungicide is used to treat this.

Fusarium root rot is caused by Fusarium fungi that live in the soil. This fungus loves asparagus and will increase in beds over time. The only way to control it is to keep the crowns healthy. Healthy crows are able to fight off the disease better. Any affected crowns will develop a brick-red rot that works from the outside in until the crown is killed. As these fungi live in the soil, it is best to only plant new crowns in new beds as the levels of the fungus will be lower and this will allow the plant a better chance of growing healthy crowns.

How to use

When preparing the spears for cooking, hold a few spears at a time by the ends–one in each hand. Gently bend the spears. The spears should naturally break where they start to become woody. Compost the woody ends and cook the ones with the tips. Pan-frying in olive or roasting spears in the oven are very common ways of cooking asparagus. Some like to boil it.

It’s a very versatile vegetable. It’s good in soups, paired with eggs, and even thrown into pasta. Asparagus also freezes well. You will want to blanch the spears in boiling water for 1.5-2 minutes. Then remove and place the spears into ice water to stop the cooking process. Drain them and place them into freezer bags or vacuum-seal bags.

• Drought tolerant once established
• Heat tolerant
• Deer resistant
• Rabbit resistant 

When starting from seed, use a transplant bed. Crowns need to be planted deeply for good harvests. The transplant bed will allow the crowns to develop. Once they are one-year-old they can be dug up and moved to their permanent bed. 

Good preparation of the permanent bed is essential for asparagus. As the plants can live 20 years, having soil they like with the nutrients they need is critical. A soil test will help you get the bed ready. 

Wait to harvest for 3 years when starting from seed and 2 years when starting from crowns. The crowns need this time to put their energy into developing healthy crowns. Waiting will result in more bountiful harvests. 

Bottom watering and good spacing will help prevent various fungal diseases. 

Sources:

Michigan State University: Growing asparagus from home

University of Minnesota Extention: Asparagus Beetles

Rareseeds.com

Burpee.com