How to Grow Asparagus
By Cindy Murphy
In some parts of the country it grows wild, and in others it is a significant cash crop. Word of its first appearance, whether in the garden, grocery store or fencerow, creates a wave of whispers among friends eager to experience that sumptuous springtime flavor. I’m talking about asparagus, not some elusive springtime mushroom. A harbinger of longer days and delicious dinners, asparagus is a wonderful spring sight, and it has been for centuries; following is all you need to know about how to grow asparagus.
Records indicate asparagus is one of the earliest vegetables humans ever cultivated. It is thought to have been first grown by the Macedonians in approximately 200 B.C., and appears in Egyptian tomb drawings as early as 4000 B.C. The ancient Greeks and Romans used it for medicinal purposes; the Greeks believed it was a cure-all for nearly every ailment. It spread throughout Europe when the conquering Romans brought it with them to foreign lands. In France in the 1600s, King Louis XIV ordered greenhouses built for it to suit his lover’s belief that it improved his prowess behind closed doors. From Europe, asparagus was brought to the newly formed American colonies, and entrenched itself both in the wild and in our gardens.
Packed with minerals and vitamins, asparagus is a powerhouse among vegetables, delivering a more complete balance of nutrients than any other. It’s teeming with good things such as vitamins A, B6 and C, with iron, potassium, riboflavin, niacin and thiamin. High in fiber and low in carbohydrates, asparagus contains no fat, no cholesterol and has only 20 calories per ½-cup serving.
A serving also provides more folic acid and glutathione than any other vegetable. A single serving of asparagus has more than half the recommended daily allowance of the folic acid needed for blood cell formation, prevention of liver disease and decreased risk of neural tube birth defects. Studies conducted by the National Cancer Institute found glutathione, a potent cancer-fighting agent, to be higher in asparagus than any other food tested.
Cultivate an interest
The place of asparagus as a nutrient-rich vegetable can’t be disputed, but for a vegetable that has been cultivated for millennia, there are plenty of differing opinions about how to grow it – ranging from what type of soil to what the optimum pH level of that soil should be; how much water it requires, when to harvest, how to harvest and what size spears are the best. Even the proper way to eat asparagus is the subject of heated discussion. All of this conflicting information might make growing asparagus seem daunting to the home gardener, but all it takes is some preparation and patience. Considering the health benefits it provides, and also the price of fresh asparagus in markets, it is well worth the effort to grow your own.
Asparagus, a member of the Lily family, is one of only a few perennial vegetables. Its name, from the Greek word asparogos, means shoot or sprout. When most vegetable seedlings are too tender to plant outside, or still but a seed containing a dream, asparagus is already thrusting its delectable spears through the spring soil. A bed of asparagus is sometimes called a “lifetime planting.” The plants can yield spears for an average of 15 to 20 years, and sometimes for as long as 50 years, although the spears tend to get smaller as the plants age.
Native to Eurasia, where it grew seaside along the Mediterranean coast and British Isles, wild asparagus has been enjoyed for centuries. In America, this wild variety can often be found growing along roadsides and in dry fields. A friend of mine in Colorado makes annual asparagus hunting treks along the railroad tracks near her town; she considers it a rite of spring. Sometimes called “sparrowgrass,” a corrupted form of “sparagus,” wild asparagus stalks are smaller and less straight than cultivated varieties. Finding its way into gourmet restaurants and markets, it’s prized for its robust, earthy flavor.
Because asparagus needs to go through a season of dormancy, it generally doesn’t last long in regions with mild winters. Most of the asparagus grown in the United States comes from Michigan, New Jersey and the West Coast states. Among other traits, asparagus varieties were bred for cold-hardiness, although breeders are experimenting now to develop varieties that can withstand long, hot summers and milder winters.
Most asparagus plants sold today are hybrid varieties. Asparagus grown in this country was originally from non-hybrids of the Washington variety – Mary, Martha and Waltham Washington. The important difference, between the hybrids and these older varieties, is the number of female plants. The older varieties can be either male or female plants; the majority of asparagus hybrids are all male.
After the harvest season, female asparagus plants produce berries. Any plant uses a great deal of energy to produce seed, and asparagus is no exception. This energy the plant expends results in fewer spears the following spring, though the spears from female plants are larger than from male plants. Popular time-tested hybrids (all male) are the Jersey varieties – Jersey Knight, Jersey King, Jersey Supreme and Jersey Giant, with Jersey Knight being the variety most asparagus growers use for fresh market. Purple Passion, which loses its purple color when cooked, is also popular with gardeners for the color it adds to salads when used raw.
Favored in Europe and in gourmet restaurants, white asparagus has a sweeter flavor than green asparagus. Though it’s a common misconception, white asparagus is not a variety of asparagus. It’s simply the manner in which it’s grown. Soil is heaped over the crown of the plant to prevent sunlight from prompting the production of the chlorophyll that makes the plant green. The spears are harvested in the early morning hours, just as the tips of the shoots break through the mounded soil.
Treat it right
When planting asparagus, bed preparation is essential and, ideally, should be done the year previous to planting; fall is an excellent time to begin preparation. Rich, fertile soil is not necessary. Remember, its native location was the sea coast, so asparagus prefers sandy, well-drained soil in full sun. It won’t mind growing in very sandy soil, but neither will it mind if you boost the organic matter in the soil with the addition of compost or manure. Asparagus roots are deep, so a well-drained location is crucial; it won’t tolerate heavy clay or soils that are continually wet.
A soil test should be performed before planting. Simple, easy-to-use soil test kits can be purchased from most nurseries, or contact your local county extension service for more extensive testing. Asparagus requires a neutral to high pH level (a “sweet” soil). Optimum pH is approximately 7.0 to 7.5, though a bit lower or higher is acceptable. If a soil test shows a low pH level, add garden lime in accordance with the package directions. Asparagus will grow in soils with lower pH levels, but research indicates that the lower levels promote the growth of Fusarium fungus, which attacks and eventually kills the plants.
Asparagus spears come from the crown of the plant. There are varied opinions about which is better to plant – the crown or seed. It’s thought that when planting from seed, diseases are less likely to be introduced into the bed. But the amount of time it takes a seed to grow to a crown mature enough to harvest from is lengthy, therefore asparagus is generally not directly seeded into the bed.
Most often one- or two-year-old crowns are planted – one-year crowns are preferable because they are less likely to suffer transplant shock than the larger, older crowns. Plant them 6 to 8 inches deep, leaving 2 to 4 feet between them to allow the ferns ample room to grow.
Don’t fill in the planting hole or trench completely. Cover the crowns with approximately 3 inches of soil, and water them in thoroughly. Using a root stimulant mixed in the water according to the package directions will help ensure the success of the new plantings by enhancing root development and reducing transplant shock. Wait about 6 weeks – enough time for the plants to sprout through the first 3 inches and start growing strong, then add another 3 inches of soil. When the plants go dormant in the fall, fill in the remainder of the furrow.
Once the plants get established – after the first year or so – asparagus needs little water except in drought or arid conditions. It is a deep-rooted plant with roots systems reaching to 10 feet, is native to sandy soil and is well able to withstand dry conditions. It doesn’t require a lot of fertilization either, using only small amounts of nitrogen and phosphorus. Asparagus does have a relatively high potassium requirement, (the last of the three numbers on a fertilizer bag: nitrogen, phosphorus, and potash or potassium). Potassium provides overall plant health by aiding in a plant’s cold-hardiness and ability to fight off the effects of drought, disease and pests. To add potassium, organic gardeners can apply a side dressing of greensand, available in most nurseries. Banana peels are also an excellent source of potassium and provide organic matter to the soil – and the worms love them.
To cut or to snap
A spear of asparagus can grow 10 inches in a single day. You’ll have the urge to pick those tender green shoots almost as soon as they appear; don’t. Resist the temptation for one, two, even three years after planting, depending on the vigor of the plant. Remember you are harvesting part of the plant, not the fruit. Shoots eventually grow into the fern, which provides energy to develop a healthy crown and strong root system. Harvesting too soon will result in a weak plant.
The second or third year after planting the crowns, begin harvesting. Harvest usually lasts for about six to seven weeks in spring and early summer. Spears ready to pick are usually between 8 and 10 inches tall and with the tips still tightly closed. Contrary to popular belief, the larger diameter spears are of better quality and most tender. “Whips” – or the smaller diameter spears – are tougher because most of asparagus’ fiber is contained in the skin. When the number and diameter of the spears ready to pick decreases considerably, the crown is starting to show signs of stress and harvest season is done.
There are two methods of harvesting the spears: either cutting or snapping them from the crown. Most of the world cuts them, but according to the Michigan Asparagus Advisory Board, its state – which ranks third in the nation in asparagus production behind California and Washington – likes to boast Michigan’s asparagus is unique because it’s hand-snapped above the ground. It makes no difference to the plant. The advantage to either method is in cooking and storage. When snapping the spear, it will generally break off above the woody, inedible butt-end, so it will not need to be trimmed.
Cutting below or at the soil surface leaves the fibrous end attached to the spear, which must be removed before cooking. This butt-end helps the spear retain moisture so it can be stored for a longer period of time. For best quality, fresh asparagus should be kept refrigerated and used within two to three days. Wrapping a moist paper towel around the ends, or standing the spears upright in a container filled with a couple inches of water in the refrigerator, helps to maintain freshness. To preserve your harvest further, asparagus can either be canned or frozen after blanching.
Feed the future
Asparagus, as a perennial, requires a bit more work than most vegetables after harvest. After the end of the asparagus harvest season, post-harvest duties continue through summer and into autumn. The ferns should be allowed to grow throughout the season. They can get quite large – up to five feet tall. Resist the urge to prune them or, worse, cut them to the ground during summer. The asparagus fern feeds the crown and roots, supplying energy needed to produce next year’s crop. Keeping the fern healthy throughout the post-harvest growing season helps ensure an increased yield and better quality for the next season.
Keep the bed weeded, and control disease and insects. The most common disease problems with asparagus plantings are fungal. Because treatments aren’t typically 100 percent effective, prevention is crucial. Buying disease-free crowns, planting in a sunny, well-drained location and keeping beds well-maintained are the best forms of prevention. Rust is a fungal disease carried by the wind; the spores overwinter on asparagus plant debris and affect new growth the following season. Remove the ferns from the area in fall; if you have rust, don’t compost. Fusarium is a soilborne fungus. Control is directed at minimizing infection early in the bed by using good cultural practices. Some studies suggest the plants’ susceptibility to Fusarium may be reduced by adding mycorrhizal fungi, which feed and help protect plants from drought, to the soil when planting.
The biggest threat from insects comes from asparagus beetles. They feed on the shoots in spring and the foliage in summer. Removing them by hand is the best organic control, and removing the ferns in fall will eliminate the beetles from overwintering. Got chickens, ducks or geese? Turning them loose in your asparagus bed will help control the beetles.
Mulching asparagus plantings is a good practice. In summer, it helps control weeds and keeps moisture in the soil. In colder climates, it helps protect the crown during winter and stimulates the shoots so they emerge earlier. A generous application in fall – up to 1-foot thick – is not too much.
Any fertilizing should stop after about the first of August. When the ferns start to turn yellow in fall, they can be cut to the ground, and the foliage removed. Or leave them be a while longer – they’ll turn a wonderful rich, deep golden color that is attractive in the autumn landscape.
Take it to the table
With a little bit of effort and time, you can serve one of nature’s most healthy and delicious foods – coming right from your garden to your table. And speaking of tables, this brings us to the last point of contention concerning asparagus: table etiquette. It’s long been debated which is proper – eating asparagus with your fingers, or with a fork and knife. General consensus says if it’s covered in sauce, use eating utensils. Otherwise, many manner experts agree it should be eaten with your fingers.
However you choose to eat it, asparagus should never be overcooked. It is best when served firm, but tender, and it takes a very short time to cook.
My favorite way to serve asparagus is roasted. It’s quick and easy, and roasting brings out a sweeter, more flavorful taste. Spread a single layer of washed spears in a shallow baking dish. Drizzle with olive oil, and add salt and pepper to taste. I like to add a squeeze of lemon juice and a dash of balsamic vinegar for some zing. Roast covered in a preheated 350°F oven for about 10 to 15 minutes, checking with a fork to determine desired tenderness. Enjoy!
Cindy Murphy lives in West Michigan, where her asparagus bed is plagued by only one pest, her husband, who eats more spears right out of the garden than he brings into the house to cook.
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