Growing Asparagus

Bundle of asparagus spearsAsparagus was first cultivated about 2500 years ago in Greece. Asparagus is a Greek word, meaning stalk or shoot. The Greeks believed asparagus was a herbal medicine which, among other things, would cure toothaches and prevent bee stings.
Second century Physician, Galen, described asparagus as “cleansing and healing”. Claims for medicinal benefits of asparagus persist to this day. The Romans became great lovers of asparagus, and grew it in high-walled courtyards. In their conquests, they spread it to the Gauls, Germans, Britains and from there, the rest of the world.

The asparagus plant is a member of the lily family, which also includes onions, leeks and garlic.

Asparagus is a hardy perennial. It is the only common vegetable that grows wild along roadsides and railroad tracks over a large part of the country. Although establishing a good asparagus bed requires considerable work, your efforts will be rewarded. A well-planned bed can last from 20 to 30 years. For this reason, asparagus should be planted at the side or end of the garden, where it will not be disturbed by normal garden cultivation. Asparagus is one of the first vegetables ready to harvest in the spring.

Calendar

  • Harvest early Spring through June.
  • After harvest, fertilize with 12-12-12 at 2 pounds per 100 square feet.
  • Snap off all remaining spears.
  • In the fall after the first freeze, trim the fern a few inches from the ground.

Recommended Varieties

The list of commonly available varieties has significantly changed in recent years. Standard varieties include:

  • Mary Washington
  • Martha Washington
  • Waltham Washington

They are still being offered; but a number of new varieties that are either predominantly or all male recently have been introduced in to common usage. Asparagus plants are naturally either male or female. The female plants bear seeds, which take considerable energy from the plant and sprout new seedlings, which cause overcrowding in the bed. Male plants produce thicker, larger spears because they put no energy into seeds and have no weedy seedling problem. A line that produces only male plants was discovered and has been incorporated into some truly amazing varieties.

  • Jersey Giant
  • Jersey Knight
  • Jersey Prince
  • Syn 53
  • Syn 4-362
  • UC 157
  • Viking KBC

These are new hybrids with larger yields. It is advisable to plant the best variety available, as an asparagus bed should remain productive for at least 15 to 20 years. If you are starting a new bed, you may never get to choose a variety again if your bed produces that long. All the newer varieties are cold tolerant and are resistant to rust and fusarium.

Select the new all-male hybrid asparagus varieties such as Jersey Giant, Jersey Prince, and Jersey Knight. These varieties produce spears only on male plants. Seeds produced on female plants fall to the ground and become a seedling weed problem in the garden. Female plants also have to expend more energy to produce the seeds that decreases the yields of asparagus spears on female plants. The all-male hybrids out-yield the old Mary Washington varieties by 3 to 1.

The Fern

The asparagus fern is the key to growth. It is the conduit to the crown and provides nutrients to the roots for next year’s crops. It should not be trimmed until the first frost.

Soil requirements

Asparagus grows in most any soil as long as it has good internal drainage. Asparagus roots do not like waterlogged soils which will lead to root rot. It prefers a soil pH of 6.5-7.5., and will not do well if the pH is less than 6.0. Have the soil tested to determine phosphorus and potassium needs; or add 20 lbs of a 10-20-10 or similar analysis fertilizer per 1,000 square feet, tilled to a 6 inch depth before planting.

When to Plant

Asparagus should be planted as soon as the ground can be worked in the spring. One-year-old crowns or plants are preferred. Seeds are sown in a production bed and allowed to grow for a year. However, caring for the small seedlings until they become established can be time consuming. Also, because the seeds are spaced a few inches apart, the crowns will have to be dug and transplanted to their permanent, wider-spaced location in the garden after one year. The young plants have compact buds in the center (crown), with numerous dangling, pencil-sized roots. Adventurous gardeners can start their own plants from seed. Although this adds a year to the process of establishing the bed, it does ensure fresh plants and the widest possible variety selection.

Buy one-year-old, healthy, disease-free crowns from a reputable crown grower. A crown is the root system of a one-year-old asparagus plant that is grown from seed. Each crown can produce 1/2 lb. of spears per year when fully established.

Asparagus can be planted from mid-April to late May after the soil has warmed up to about 50 degrees F. There is no advantage to planting the crowns in cold, wet soils. They will not grow until the soil warms and there is danger of the plants being more susceptible to Fusarium crown rot if crowns are exposed to cold, wet soils over a prolonged period. Plant the asparagus at either the west or north side of the garden so that it will not shade the other vegetables and will not be injured when the rest of the garden is tilled.

Spacing & Depth

Place the plants in a trench 12 to 18 inches wide and a full six inches deep. The crowns should be spaced 1 foot apart. Spread the roots out uniformly, with the crown bud side up, in an upright, centered position, slightly higher than the roots. Apply about 1 lb. of 0-46-0 (triple superphosphate) or 2 lbs. of 0-20-0 (superphosphate) fertilizer per 50 feet of row in the bottom of the furrow before planting. This will make phosphorus immediately available to the crowns. Omitting this procedure will result in decreased yields and the spear production will not be as vigorous. If more than one row is planted, space the rows five feet apart from center to center. Wide between-row spacing is necessary because the vigorously growing fern will fill in the space quickly. Wide spacing also promotes rapid drying of the fern to help prevent the onset of fungus diseases.

Cover the crown with two inches of soil. Gradually fill the remaining portion of the trench during the first summer as the plants grow taller. Asparagus has a tendency to “rise” as the plants mature, the crowns gradually growing closer to the soil surface. Many gardeners apply an additional 1 to 2 inches of soil from between the rows in later years. However, do not compact the soil over the newly filled furrow or the emergence of the asparagus will be severely reduced. Spears should emerge within one week in moist soils.

Do not harvest the asparagus during the planting year. Spears will be produced from expanded buds on the crown. As the spears elongate and reach a height of about 8 to 9 inches, the tips will open. The spear will become woody to support the small branchlets that become ferns. The ferns produce food for the plant and then move it down to the crown for next year’s spear production.

Asparagus is very drought tolerant and can usually grow without supplemental watering because it seeks moisture deep in the soil. However, if rainfall is insufficient when planting or afterwards, it is beneficial to irrigate the crowns. Otherwise the plants will become stressed and vigorous growth will be impeded.

Care

As asparagus plants grow, they produce a mat of roots that spreads horizontally rather than vertically. In the first year, the top growth is spindly. As the plants become older, the stems become larger in diameter.

As noted, asparagus plants are dioecious (either solely male or solely female). The female plants develop more spears or stems than the male plants, but the stems are smaller in diameter. With normal open-pollinated varieties, gardeners plant both male and female plants in an approximate ration of 1:1. After the first year, small red berries form on the female plants in late summer. These then fall to the ground, sprouting plants that essentially become perennial weeds in the asparagus bed.

Because asparagus remain in place for years, advance soil preparation helps future production greatly. Working green manure crops, compost, manure, or other organic materials into the proposed bed well in advance of planting is a good approach. Asparagus should be fertilized in the same way as the rest of the garden the first 3 years. In the spring, apply 10-10-10, 12-12-12 or 15-15-15 fertilizer at the rate of 20 to 25 pounds per 1,000 square feet of area or 2 pounds per 100 square feet and incorporate with soil tillage. Starting in the fourth year, apply the same amount of fertilizer but delay application until June or July (immediately after the final harvest). This approach encourages vigorous growth of the “fern,” which produces and stores nutrients in the roots for next year’s production season.

Weed Control

Weeds and grasses are the worst problems with asparagus. They compete with the developing spears, make an unsightly area in the garden and significantly decrease yield and quality. Start frequent, light, shallow cultivation early in the spring in both young plantings and mature patches that are being harvested.

Weed control can be accomplished by hand hoeing and cultivating during the planting year since there are no herbicides labeled for use in asparagus during the first year. Labeled pre-emergence herbicides may be used during the second spring, by applying it over the shredded fern, about three weeks before spear emergence . Do not use salt as a weed killer. It will not harm the asparagus, but it inhibits water penetration in the soil. Also, rains can leach the salt out of the asparagus bed and into the rest of the garden, injuring other vegetables that are less salt tolerant than asparagus.

Harvesting

Asparagus can be harvested the third year after planting crowns, but for no more than one month the first season. The plant is still expanding its root storage system and excessive removal of spears weakens the plants. During the fourth year and thereafter, the spears may be harvested from their first appearance in the spring through May or June (as long as 8 to 10 weeks).

Harvest spears 5 to 8 inches in length by cutting or snapping. To cut a spear, run a knife into the soil at the base of the spear and carefully sever it. Because the spear is cut below the point where fiber develops, it becomes necessary to remove the fibrous base from the tender stalk. Cutting may damage some spear tips that have not yet emerged from the ground. To snap a spear, grasp it near the base and bend it toward the ground. The spear breaks at the lowest point where it is free of fiber. There is no need to cut asparagus below the soil with a knife. This may injure other buds on the crown that will send up new spears. The small stub that is left in the soil after snapping, dries up and disintegrates. A new spear does not come up at the same spot, but comes up from another bud that enlarges on another part of the crown.

Either method is acceptable. Cutting is often preferred by commercial growers and snapping by home gardeners. Asparagus deteriorates rapidly after harvest. If it is not eaten immediately, it should be processed or refrigerated.

As the tips of the spears start to loosen (known as “ferning out”), fiber begins to develop at the base of the spears, causing them to become tough. The diameter of the spear has no bearing on its toughness. When harvesting, the asparagus patch should be picked clean, never allowing any spears to fern out, as this gives asparagus beetles an excellent site to lay their eggs.

The year after planting, asparagus can be harvested several times throughout a three-week period, depending on air temperatures. Research shows there is no need to wait two years after planting before harvesting. In fact, harvesting the year after planting will stimulate more bud production on the crown and provide greater yields in future years, as compared with waiting two years before harvesting.

Asparagus spears will start to emerge when the soil temperature reaches 50 degrees F. After this, growth of asparagus is dependent on air temperature. Early in the season, 7 to 9 inch spears might be harvested every 2 to 4 days. As air temperatures increase, harvesting frequencies will increase to once or twice per day, harvesting 5 to 7 inch spears before the tips start to fern out and lose quality. The second year after planting, the length of harvest can increase to about 4 to 6 weeks. The third year after planting and thereafter, harvesting can continue for 6 to 8 weeks. Since the length of harvest season will vary from year-to-year depending on air temperature, stop the harvest when the diameter of 3/4 of the spears becomes small (less then 3/8 inch). Experience gained by growing the crop will make it easier for the gardener to know when to discontinue the harvest.

After Harvest

When harvest is finished, snap all the spears off at ground level. New spears will then emerge, fern out, and provide a large canopy to cover the space between the rows. Once a dense fern canopy is formed, weed growth will be shaded out.

Following freezing weather in the fall, the asparagus tops should be removed to decrease the chances of rust disease overwintering on the foliage.

Common Problems

Asparagus beetles are commonly found in home plantings. If numerous, they may be controlled by a suggested insecticide or by handpicking.

Asparagus rust can be a problem in the Midwest. Moisture left on the plant for 10 hours can help to spread the disease. Plant resistant varieties.

Inspect the ferns throughout the season for insect feeding and fern dieback. Asparagus beetles chew on the fern, causing the stem to turn brown and reducing the yield the next year. Spray the ferns with an approved insecticide when beetles are seen. For disease prevention, spray with an approved fungicide on a 7 to 14 day schedule beginning when the ferns reach a 3 to 4 foot height and continuing until mid September.

Do not cut down the fern growth at the end of the growing season. The all-male hybrids stay green until frost, enabling photosynthesis to occur longer throughout the season. Leave the dead fern growth intact over the winter. This catches snow for additional soil moisture and keeps the soil temperature about 5 degrees F cooler than bare soil with no covering of dead fern. The cooler soil temperature is helpful in delaying the early emergence of asparagus in the spring, when air temperatures might rise prematurely and then fall again, predisposing the spears to frost damage. Frost-damaged spears should be snapped and discarded.

Remove the old fern growth by cutting or mowing as low as possible during the first week of April. Dead stalks are very sharp and can easily skin knuckles when harvesting new spears.

Questions & Answers

Q. What causes my asparagus spears to have loose heads?

A. When the weather turns hot, the growing point expands rapidly and the bracts (modified green leaves) are spread by the early development of the stems and ferns. The asparagus is safe to eat because only the appearance is affected.

Q. Early spring freezes caused the asparagus spears in my garden to turn brown and wither. Are they safe to eat?

A. Frozen tips should be picked and thrown away. These spears, although not poisonous, are off-flavor.

Q. Can I start asparagus from seed?

A. Yes. You can grow your own plants by planting seeds 1/2 inch deep and 2 inches apart in the row. Start the seeds in the spring when the soil temperatures have reached 60°F. Dig the plants the following spring, before growth begins and transplant them to the permanent bed as soon as the garden can be worked. Growing your own plants delays establishment of your bed an additional year, but it ensures that you are starting with freshly dug crowns that have not lost vigor by being dug, stored and shipped. Also, variety selection is usually much greater when shopping for seeds rather than crowns.

Q. What causes crooked spears?

A. Asparagus spears grow quickly and are sensitive to mechanical injury from cultivation or cutting tools, insects or wind-blown soil particles. Injured areas grow slowly so that the rapid growth on the opposite side causes spears to curve toward the injured side. The cause of flattened (faciated) spears is unknown.

Selection & Storage

Asparagus is spring’s most luxurious vegetable. It was once cultivated for medicinal purposes as a natural remedy for blood cleansing and diuretic properties. During the Renaissance, asparagus was also promoted as an aphrodisiac and banned from the tables of most nunneries.

Botanically, asparagus is a member of the lily family, closely related to onions and leeks, though it bears no resemblance to them in appearance or flavor. It is a finicky plant, harvested by hand and requiring much attention during the brief growing season. Left to mature it will sprout into beautiful feathery ferns that are often used in floral arrangements.

While Europeans prize white asparagus, Americans tend to prefer the green or violet-green varieties. When buying asparagus look for compact tips and smooth green stems that are uniform in color down the length of the stem. Check the cut stem end for any signs of drying and always avoid withered spears.

Pencil thin or thick stems can be equally delicious. Contrary to popular belief, thinner stems are not an indication of tenderness. Thick stems are already thick when they poke their heads out of the soil and thin stems do not get thicker with age. Tenderness is related to maturity and freshness.

Asparagus comes in a variety of colors including white, violet-green, pink and purple. If you must store any variety of asparagus, treat it as you would treat a cut flower. Trim the stems and stand them in a glass with one to two inches of water. Cover with a plastic bag and refrigerate for 2 to 3 days or until ready to use.
Nutritional Value & Health Benefits

Asparagus is low in calories and provides substantial amounts of two antioxidants—vitamin A and C. It truly shines as a source of folate and has a goodly amount of fiber.

Asparagus is very perishable and should be harvested in the morning when air temperatures are cool. After picking, immerse the spears in ice-cold water to remove the heat; then drain the water and place the spears in plastic bags. Store in the refrigerator at 38 to 40 degrees F. Asparagus will keep for 1 to 2 weeks with little loss of quality.

Nutrition Facts

(Serving size, 1/2 cup cooked)
Calories 90
Protein 2 grams
Carbohydrates 4 grams
Dietary Fiber 1.5 grams
Potassium 144 mg
Vitamin C 10 mg
Folate 131 mcg
Vitamin A 485 IU

Preparation & Serving

Cook asparagus as soon as possible to ensure peak flavor. Spears start to lose flavor and moisture as soon as they are harvested. For this reason, imported asparagus, while still good, tends to lack flavor, making home grown Michigan and Illinois spring crops most desirable.

To prepare, wash under cool running water and trim an inch from the stem end. Use a vegetable peeler to peel an inch or two off the bottom end, if desired. The peelings can be added to the cooking water which, can be refrigerated and reused. The water becomes quite flavorful and is excellent in stock and soup.

Peeling asparagus can be tedious and many cooks prefer breaking the tough ends. To use this method, hold the top half of an asparagus spear in one hand and the bottom half between the thumb and forefinger of the other hand. Bend each spear until it snaps in two pieces. The spears will naturally break where the tender part meets the tough end. Although this method produces a lot of waste, the tougher bottoms can be saved for soup or stock, if desired.

Asparagus can be eaten raw, steamed, boiled, grilled, roasted or incorporated into casseroles and salads. Tall narrow asparagus kettles are designed to cook the spears upright, immersing the stems while the tender heads steam. It is not necessary to purchase an asparagus kettle in order to cook asparagus properly. The key to perfectly cooked asparagus is “cook it briefly.”

The flavor of asparagus marries well with many ingredients and it is equally delicious dressed simply with olive oil, lemon juice, salt and pepper. Raw asparagus is also tasty served as crudités with a flavorful dipping sauce. When using asparagus as a salad, always wait until serving time to add the dressing as the high acid content of most dressings will turn the spears yellow. Add fresh chives, savory, thyme, and tarragon to enhance the flavor of cooked asparagus.

Home Preservation

The best home preservation method to use for asparagus is freezing.

1. Select young tender spears. Wash thoroughly and sort into like sizes.
2. Trim ends and peel or use the “break method” described above. Cut spears into even lengths to fit freezer bags or freezer containers.
3. Water blanch small spears 2 minutes, medium spears 3 minutes and large spears 4 minutes.
4. Remove from blanching water and immediately immerse in ice water for 5 minutes to cool. Drain slightly.
5. Package, leaving no headspace, seal, label, date and freeze at zero degrees or below for up to one year.

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