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Asparagus Growing and Harvest Information

by chuck.mcmullan
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Where to Grow Asparagus

A member of the Lily family; Asparagus is a perennial vegetable that thrives almost anywhere in the continental United States (Zone 3-8), except where summers are exceptionally long and humid. Its native location was along the sea coast. The edible portion of the plant is the young stem shoots which emerge from the ground as the soil temperature reaches 50 degrees F in the spring. Proper soil preparation before planting and good summer maintenance will keep this vegetable yielding for a minimum of 10 years and possibly as long as 15 or more. Because it takes up permanent garden space, it should be given a specially designated spot. It is often planted near rhubarb, another long-lived garden perennial. Asparagus beds at the edge of the garden are continually raided by weeds, especially witchgrass and others that creep in from underground. We like to keep asparagus in the middle of the garden to keep them far from possible invaders.

Asparagus can be considered a power food among veggies. It is packed with vitamins and minerals, delivering a more complete balance than any other. Asparagus is a good source of vitamin A, B6, and C, as well as iron, potassium, riboflavin, niacin, and thiamine. It is high in fiber and low in carbohydrates, contains no fat, no cholesterol, and has only 20 calories per 1/2 cup serving. One serving of asparagus also provides more folic acid (1/2 the recommended allowance) and glutathione than any other vegetables. Studies conducted by the National Cancer Institute found that glutathione, a potent cancer-fighting agent, was higher in asparagus than any other food tested. An established bed of 25 asparagus plants will produce about 10 pounds of asparagus per year.

Asparagus Varieties

Because asparagus stays productive for so long, it’s important to plant the best variety available to your area. Mary Washington and Waltham Washington are both excellent rust-resistant varieties and are considered heirlooms. These are both open-pollinated varieties that will form berries after the harvest and require subsequent weeding of self-seeded asparagus plants. Plants spend a great deal of energy producing seed, and you can expect your female asparagus plants to produce a few less stalks next spring due to this. This is one reason all-male plants are preferred. In addition, the naturally occurring seedlings are difficult to pull and are often seen as weeds in a mature asparagus patch, and not desirable from a cultivation standpoint. The majority of hybrid plants are male to encourage increased spear production. Popular time tested hybrids are the Jersey varieties: Jersey Knight, Jersey King, Jersey Supreme, and Jersey Giant. Jersey Knight is the most common variety of asparagus at the market.

There are no white varieties of asparagus; rather this is controlled by how they are grown. Typically, soil is heaped over the crown of the plant to prevent sunlight from prompting the production of chlorophyll, which makes the plant green. The spears are harvested early in the morning as soon as the tips start to emerge from the soil. The white variety tends to be slightly sweeter than green asparagus.

Temperature
Germination70 - 85 F
For Growth60 - 70 F
Soil and Water
FertilizerHeavy feeder. Apply compost to first year beds in autumn, and again after harvest in spring. Beds may need P and K before planting, and N afterwards.
MulchUse straw or light material during winter. Use compost during growing season.
pH6.5 - 7.5
WaterHeavy
Measurements
Seed Planting Depth8 - 10"
Seed Depth3/4"
Root Depth>4'
Height3 - 8'
Width2 - 4'
Space between plants
In beds12"
In rows15 - 18"
Space Between Rows36 - 48"
Harvest
When spears are 3/8" thick and 6-8" high, cut 1/2" below soil surface. Heads should be tight and spears brittle. Stop harvesting when stalks are <3/8" thick.
Companions
Incompatibles Onion family, weeds during first 6 weeks of growth.

Soil for Asparagus

Since asparagus is a perennial vegetable and can produce for up to 30-50 years, it is very important to prepare the soil properly. The best soil is sandy, well-drained loam, heavily enriched with well-rotted manure and compost. Ground prepared in this way dries out quickly in early spring, to spur the early growth of the spears. The pH should be about 7.5. Average garden soil, however, will support a good asparagus crop, provided it drains well. Rocky New England soil will hamper the development of strait spears. Fertilization application: 4 pounds of 5-10-10 per 100 square feet, or generous quantities of bone meal or ground phosphate rock and wood ash. Asparagus craves phosphorus, which is usually abundant in composted manure and kitchen waste compost. If you can fit it in your gardening schedule, prepare the asparagus bed in the late summer or fall to be ready for planting the following spring. This provides a chance to plant a nitrogen-fixing green manure crop like buckwheat. Asparagus has a pretty good appetite for nitrogen.

Choose a spot that is free of perennial weeds and grasses.

Planting Asparagus

As soon as the ground can be worked. Plan on an average of 10 plants per person. Plant in a sunny spot protected from the wind. It can tolerate some shade but is most productive in full sun. There is not a lot of surface area on asparagus’s delicate fern-like foliage, so it needs all the sun it can get.

Asparagus tips emerging from the ground

How to Grow Asparagus

Slow way

Planting asparagus from seed has some advantages and disadvantages. It is a little bit more work, but typically costs much less also. The biggest disadvantage is you will have to wait an extra year to harvest your first spears. The crowns you would purchase at your local nursery are already 1 year old, so they would start producing that much faster.

Asparagus seeds can be started indoors, or sown directly in the garden. Asparagus seeds started indoors should be started in 4-inch pots approximately 3 months before the last frost. They will germinate best at daytime temperatures at around 75-80 F and a low temperature at night of around 65F. It may take as long as 3 weeks for the asparagus seeds to germinate. To hasten germination, soak the seed for 48 hours in water prior to planting. Sow the seeds approximately 1/2″ to 3/4″ deep in rows approximately 2 feet wide. Seedlings should be transplanted or thinned to a minimum of 3-4 inches between plants. These seedlings should grow for a summer, and the following year the ‘yearlings’ should be transplanted to the permanent asparagus bed. Follow the directions below for transplanting asparagus crowns.

Fast way –

Buy year old plants or ‘crowns’ from the seed store or your local nursery. They will have compact buds with masses of supple dangling roots. Asparagus crowns should be planted in the springtime for cooler regions, about the same time daffodils are in bloom. In very warm regions, asparagus should be planted in the fall or winter. Plants are set out in trenches dug to a depth of 6-8 inches and spaced 2-4 feet apart, in the prepared soil bed. Mound the soil to the side of each trench, as it will be used to back-fill as the asparagus grow. Set the asparagus crowns in the base of the trench with 18 inches between the plants, and cover with about 2 inches of soil. As the asparagus tips grow the trenches will be filled in gradually until they are completely filled by the end of the summer. Asparagus plants have a tendency to rise as they grow mature, hence the need for the trenching method of planting.

How Asparagus Grows

The roots will spread horizontally rather than down, and in years to come will produce a thick mat of roots and underground shoots. The first year after planting the spears will be spindly and thin. As they mature, they develop into tall, ferny branches quite lovely to see. The true asparagus leaves have been reduced to the triangular scales on the spears which are cut off when the asparagus is cut for cooking.

Cultivating Asparagus

Weeds are the biggest problem with asparagus since they offer too much competition for the developing shoots, and in an untidy asparagus patch, they can develop very quickly. Any weeds in the asparagus patch will divert nutrients away from the asparagus and affect its yield and longevity. Companion plants can also be considered weeds since they will also divert nutrients away from the asparagus. Use them sparingly, if at all. Frequent hand weeding early and often is the best way to control weeds, especially in the first two/three years of growth. Frequent cultivation and light mulching with grass clippings, or hay are good preventatives. First cultivation should be in early spring, before the spears appear above ground. At this time, lightly apply fertilizer, preferably well-rotted manure, to each plant, and continue cultivation until the tops have grown too high and thick to manage with a shallow hoe. Also, watering is extremely important any time there is a lack of adequate rainfall during the growing season.

The ferny top growth of asparagus is actually producing food for the shoots below in much the same manner as bulb foliage renews a bulb underground for next spring’s flower. For this reason, asparagus foliage should not be cut down too soon near the end of the season but should be allowed to wither off naturally. The thick growth of asparagus ferns or brush that covers the bed in late summer and early fall will turn brown and brittle at the end of the growing season. In early to mid-fall after several hard freezes, cut this brush and add it to the compost pile to interrupt the life cycles of insects and diseases. This is a good time to add soil amendments if necessary, and spread a 3-inch layer of compost followed by a thick (6″) layer of straw to protect the asparagus crowns from winter damage and allow soil organisms to continue improving the soil in both the fall and spring.

Fertilizer for Asparagus

As far as vegetables go, asparagus has a pretty big appetite for fertilizer. Asparagus needs to produce enough energy to survive the winter, feed us, and then produce a few new ferns. It may be possible to overfeed asparagus, but it isn’t easy. To ensure a steady supply of nutrients for the plants and keep soil organisms busy loosening and aerating the soil, apply a thick layer of weed-free compost topped with three inches of straw, rotted sawdust, or mulch after harvesting is complete, and again in the fall after cleanup. This will help to encourage succulent spears the next spring. Clean spears will push up through the mulch in the spring, there is no need to remove any leftover mulch in the spring.

Storage Requirements
Asparagus looses it's flavor quickly, and is best eaten fresh. For storage: wrap spears in moist towels or stand upright in a glass of water, then refrigerate in plastic bags. Blanch before freezing.
Fresh
TemperatureHumidityStorage Life
32 - 35F95 - 100%2 weeks
Preserved
MethodTasteShelf Life
CannedGood12+ months
FrozenExcellent12 months
DriedFair12+ months

Harvesting Asparagus

The succulent tenderness of asparagus depends on the quality of the soil, the rapidity of shoot development in spring, and adequate soil moisture. No harvesting will occur the first year plants are set out, a few spears may be cut the second year(2-3 spears/plant), and full harvest will be available the third year. At a full harvest year, cutting may last for 4-6 weeks, depending on the growing season and how well the asparagus plants have been managed. Harvest spears that are more than 3/8″ in diameter and 6-10″ tall. The skinny spears should be left to grow into ferns. Stop harvesting when the emerging spears are small and the tips become loose and open; it is also advisable to stop harvesting once the weather has become too warm. At the beginning of the harvest period, spears may be ready 2 or 3 times a week. It is possible they could grow up to 10 inches per day, so they will need to be checked daily during peak production. They are tastiest when just about 6 inches tall and tight at the tip, not spreading. There are two schools of thought on cutting. One is to cut the spears off with a sharp knife just at ground level to avoid damaging any underground roots. A simpler method is to snap the spears off at ground level.

Asparagus is similar to corn in that quality deteriorates quickly after picking. For the best flavor, pick it just before it is to be cooked. If this isn’t feasible, refrigerate it promptly. It will store best if left in a standing position, with the thicker end submerged in 1-2″ of cold water for a few minutes. The spears can then be drained and refrigerated in plastic storage bags for approximately 7 days.

Asparagus Pests

  • Asparagus beetles are the main pest that damages asparagus fronds. There are two common species, the common asparagus beetle (black, white, and red-orange) and the spotted asparagus beetle (red-orange with black spots), both of which are about 1/3 inch long. They can effectively be hand-picked from the plants when found, look for them in the morning when it is too cool for them to fly. The beetles overwinter in the plant debris, so removing fronds in winter will reduce their numbers eventually. Lady beetles and several small wasp species are major asparagus beetle predators that are naturally occurring.
  • Asparagus beetle eggs look like stubby brown hairs. Wipe them off the spears with a damp cloth. Asparagus beetle larvae are soft, grey, slug-like creatures with blackheads that are unable to crawl back up into position if swept off the plants. Many gardeners allow their chickens to pick through the asparagus beds for 3-5 days over winter to eliminate any leftover beetles. If you have a problem and don’t raise poultry, setup a spring trap crop. Don’t cut the spears in spring within this plot, and patrol often to collect as many adult asparagus beetles as possible. In late summer cut the fronds 2 inches from the ground and compost them. In three weeks or so, you can harvest a fall crop of spears from your trap crop plot.

Diseases for Asparagus

Rust has been virtually eliminated by the development of rust resistant varieties.

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