How To Grow Asparagus
This is my garden guide on how to grow asparagus.
While learning how to grow asparagus is a big time commitment, because asparagus takes three years from when it is first planted to produce stalks you can eat, it can be a very rewarding and fun experience, and if you grow enough, it can be a money saving endeavor as well.
The asparagus in grocery stores is sold by the pound, and so sometimes it is on sale when the stalks are old and the stems have turned woody – which means it will weigh more and provide less edible greenery.
In terms of usable portions, this is very expensive. Organic asparagus can go for as much as eight dollars a pound where I live.
If there were ever a good argument for learning how to grow asparagus, the price and quality of what is available in supermarkets should be enough.
Although it will take a few years to become established and begin producing, learning how to grow asparagus is fairly easy. Asparagus can be eaten fresh, as soon as it is picked, or frozen, dried, or even pickled and canned so that it will keep for years. Once you have learned how to grow asparagus and gotten a bed set up in your backyard, if you care for it correctly, it can last for as much as twenty to thirty years.
In this guide on how to grow asparagus, I will begin by telling you all about the history, biology, and different varieties of asparagus available to the home gardener. Like many modern vegetables, asparagus has a rich tradition of cultivation by people that dates back thousands of years, and it has not changed much in that time.
Once we know a bit about the plant itself, I will turn the focus of the guide over to how to grow asparagus, beginning with selecting the site for the asparagus bed, preparing the bed by double digging, applying compost and fertilizer, and making sure the nutrient content and pH are correct. Then I will describe how to grow asparagus from seed or by planting asparagus crowns, which are the root structures from which the rest of the plant will grow.
After we have covered how to get the asparagus started in the garden bed, I will discuss how to care for and maintain your plants for the first two years of growth, so that you can successfully get them to the third year, when they will begin to reward you with edible stalks. While you will of course have to continue to take care of your bed for the entire span of its life, these first two years are critical to ensuring that all of your hard work pays off.
It is no fun to prepare a bed, select and purchase special varietals for your garden, and nurture them for a year or two only to have them die off because the site you selected was not correct or because pests or disease killed off your crop.
This section on care and maintenance will cover fertilizing your plants for the first two years, how to water your plants to make sure they are kept evenly moist without becoming waterlogged, how to keep weeds down without disturbing the soil or the root systems of the asparagus plants, and preventing the spread of disease or proliferation of pests in your asparagus bed, as well as in your garden as a whole. These are all very important aspects of how to grow asparagus successfully, and I urge you to pay special attention to this section.
Finally, I will discuss how to harvest your asparagus plants once they have produced edible stalks, as well as how to grow those stalks to produce white asparagus, a rare and enjoyable delicacy for your table. In this section I will also cover a few methods of saving asparagus for longer than a few weeks.
All set? Let’s get started learning how to grow asparagus!
1. All about Asparagus
Asparagus is a member of the lily family. People originally learned how to grow asparagus near the Mediterranean Sea, and it was considered a valuable delicacy by the ancient Greeks. Methods for growing this vegetable were described as early as 200 B.C., and modern cultivars of asparagus have changed very little since then. It was cultivated as far north and west as England by 0 A.D. and it was brought to the Americas by early colonists.
Asparagus is a perennial vegetable that can be grown in the same garden bed for as long as twenty to thirty years. It has an underground network of fleshy roots for storing nutrients as well as a network of underground stems known as rhizomes. These roots store food and produce the asparagus spears. The root system is referred to as the plant’s crown. When the air and soil temperature warms up, buds will develop on the rhizomes. These buds are what will eventually become the edible spears of the plant. If the spears are not harvested, they will develop into a green, fern like bush that can grow to be between four and six feet tall. The leaves of the bush will produce food for the plant, which will then be stored in the storage roots belowground, and will be used to nurture the spears produced in the following growing season.
Asparagus is a dioecious species of plant, which means it has separate male and female plants. It is one of the few dioecious species that is grown in backyard vegetable gardens. Insect pollinators such as bees transfer the pollen between the flowers of the male plants and the flowers of the female plants. The female plants will then produce bright red berries in the fall. It should be noted that these berries are poisonous, so you should be sure to keep small children and family pets away from your asparagus patch. The female plants use up a lot of their energy on the production of these berries, which contain the plant’s seeds. Because of this, the female plants do not produce as much or live as long as the male plants.
Asparagus is a cool season crop that will do best in climates where the soil freezes over the winter to at least a few inches belowground. In many southern locations in the United States, and especially along the Gulf Coast, ambient temperatures remain too warm over the winter to successfully grow asparagus. Without cold winters, the plants will not store much nutrient material in the roots, and very few spears will be produced as a result. However, asparagus can be grown in southern California, where summer temperatures can reach as high as 100 degrees Fahrenheit in the summer, and its range extends to far northern areas where winter temperatures can dip to 40 degrees below zero in the winter.
1a. Asparagus Varieties
All asparagus varietals will grow just fine anywhere in the United States, although some will fare better in some regions than others. However, generally speaking you should feel free to select the asparagus you want to grow in your backyard based on your own personal tastes, and understand that it you can learn how to grow asparagus of any variety with a bit of trial and error.
The majority of asparagus cultivars grown in the United States are derived from the Martha Washington and Mary Washington cultivars. These are open pollinated varietals that were developed by the U.S. Department of Agriculture (USDA). Popular open pollinated varieties include Mary Washington is the cultivar that is most commonly grown in the South and is probably one of, if not the most important and widely grown cultivars in the United States; Argenteuil, also referred to as Precoce D’Argenteuil; and Conover’s Colossal. In northern latitudes of the United States and Canada, a cultivar called Viking may be successfully grown.
On the West Coast, Mary Washington and several strains of asparagus bred specifically for cultivation in California are recommended. In the Midwest and East Coast, the Rutgers Beacon cultivar does very well, and certain cultivars of the Washington variety, such as Waltham Washington, are often grown successfully in home gardens. These cultivars are all naturally resistant to asparagus rust. All of the above listed varieties are excellent options for backyard gardens, especially for growers who are just learning how to grow asparagus. They are available at garden centers as crowns. Besides that, I would encourage you to try to grow one of these open pollinated varietals from seed as well, because they allow you to save the seeds. That way, if you ever lose a crop, you will already have seeds on hand to start anew the following season.
2. Planting Asparagus
In this section on how to grow asparagus, I will explain which area of the garden is best to plant your asparagus in, how to prepare the garden bed for planting asparagus, and how to grow asparagus by starting it indoors, planting seeds or planting crowns.
2a. Selecting the Site
Asparagus should be planted along with other perennial crops on the north or east side of the garden so that it does not shade other vegetables. It can be grown successfully along a fence in full sunlight. Make sure the bed is not located in a low lying area of your yard or in an area that tends to get flooded or have standing water after rain storms.
2b. Preparing the Bed
The single most important aspect of how to grow asparagus is to make sure the bed it is grown in has adequate drainage. If the roots of the asparagus plant become waterlogged, the plant will die. It’s that simple. Raised beds are an important tool for how to grow asparagus that does not suffer from waterlogged roots.
The next most important consideration for how to grow asparagus is soil pH. Asparagus prefers a soil pH that is as close to neutral (7.0) as possible. How does Asparagus grow? Asparagus grows poorly if the soil pH is below 6.0, so the soil should be tested and the pH adjusted if it is necessary. Thus, because of the long time frames necessary for lime and other soil pH amendments to work, an asparagus bed should be tested for pH using a home kit or by sending samples to a laboratory, and the soil pH correctives added, in the fall prior to the transplanting of crowns or seedlings the following spring.
The third most important aspect to how to grow asparagus is light. Asparagus needs at least six hours of full sun a day. Fourth, asparagus beds should be about four feet wide and one to two feet long for each plant – so if you are preparing a bed for how to grow asparagus, make it four feet wide and multiply the number of plants by 1½ to determine the necessary length. Make sure the long side of the bed faces south or east for the greatest amount of sun.
2c. Double Digging the Bed
The other major consideration for how to grow asparagus successfully is to make sure the garden bed has plenty of reserve facility. This is accomplished by double digging the bed, incorporating fully aged compost into the bottom of the double dug trenches, and working even more compost – at least four to six inches – into the top of the bed. This can all be done in advance. Double digging has several advantages, and I often recommend it when you are preparing a garden bed. It allows you to add vital organic matter to the soil, which your vegetables will find invaluable to their healthy growth and development. And it allows you to break up and aerate the soil. In addition to constructing a raised bed, double digging is one of the best ways to make sure a garden bed has good drainage and is properly aerated to allow for healthy root growth. When you are preparing a bed for how to grow asparagus or other plants that depend on extensive root systems, it is very important to double dig the bed before planting your crops.
To double dig the bed, start on one side of it and dig a trench that is twelve to eighteen inches deep. Add compost as described above. Then, working your way toward the center of the bed, dig a second trench next to the first. Add compost to this one as well, and repeat until you have worked your way across the entire bed. After you have worked your way across the entire bed and added compost to the last trench, fill it in with the soil from the first trench. Be sure not to walk on top of freshly double dug areas of the bed, as this will compact the soil and defeat part of the purpose of double digging the bed in the first place.
2d. Nutrients and Minerals
Then, a month or so before you plant your asparagus, add trace minerals and then use organic sources to correct any deficiencies in major nutrients. As with pH, you can send soil samples to a laboratory to get a full report on the nutrient content and deficiencies in your garden bed, and it is generally a good practice to do this for the entire vegetable garden every couple of years. The use of organic sources is especially important for how to grow asparagus because you will not be able to simply till more fertilizer or nutrients into the bed later: asparagus takes three years to produce edible shoots, and the plants last as long as twenty years. Anything added later can only be mixed with compost and applied as a top dressing.
2e. Fertilizer and Top Dressing
If you’re wondering how to fertilize Asparagus, about one to two pounds of 5-10-10 fertilizer per 100 square feet should be worked into the soil before planting. Alternately, you can use an organic matter equivalent to this formula, and if you have double dug the bed and added sufficient material as described above, you can usually forgo it altogether. The annual spring top dressing should be five cubic feet of compost per four foot by eight foot bed. I recommend mixing three pounds of wood ash, one pound of lime, two pounds of bone meal, two pounds of alfalfa meal, and one pound blood meal into the compost before you apply it, and then cover the top dressing with a two inch layer of clean straw.
There is one final very important thing you have to keep in mind when you are selecting a site and preparing a bed for how to grow asparagus. Asparagus loves arsenic, and it will suck it up like a vacuum cleaner, and pass it on to anyone who eats it. This will not be a problem unless the site you select for the bed is in an old apple orchard that was treated with arsenic as an insecticide, but one thing you absolutely have to avoid is pressure treated wood that has been treated with arsenic compounds being anywhere near your asparagus bed. Pressure treated wood boards will be marked with green on their ends. All you have to do to keep your asparagus safe is to keep pressure treated wood away, and do not grow anywhere arsenic was used heavily in the past.
Now that you know how to select the site and properly prepare the bed for how to grow asparagus, let’s learn how to plant it.
2g. Starting Asparagus from Seed
You will find that learning how to grow asparagus from seed is not too difficult. You should start asparagus seeds indoors about six weeks before the last frost, and plant it outside around the same time you plant your tomatoes. Because some of the seeds will be male and some of them will be female, and only male plants will produce a robust crop of edible shoots, you should start twice as many plants as you think you will need. Transplanting Asparagus seedlings should be done in two rows in your garden bed, about six inches apart. The next year, cull all of the female plants but leave the two strongest ones – you will keep these so that you can gather and save seeds. Whether you are learning how to grow asparagus from seed or by planting crowns (which is covered below), you should remember that this will have to be a relatively permanent planting, and prepare the bed accordingly.
2h. Planting Asparagus Crowns
Asparagus crowns can be planted early in the spring, as soon as the soil can be worked and the last frost date has passed. Healthy crowns that are one year old should be planted in a furrow that is eight inches deep. The crowns should be placed about a foot apart in the row, and should be given at least three feet of space between rows. If you are only planting a single row, you should leave at least three feet of space between the asparagus row and the rest of the vegetables in the garden. The roots should be spread out in order to allow the crowns to lie flat in the furrow. You should then cover the crowns with two inches of topsoil. During the season, continue to gradually fill in the rest of the furrow, but be careful not to cover up the leaves of the growing asparagus plant.
It is very important that you maintain good leaf development of the plants after you have harvested the asparagus spears. Allow the tops of the asparagus plants to continue growing until the first hard frost. After that, you can remove the tops and put them in your compost pile, or shred them and use them to mulch the asparagus furrow. However it is usually better to opt for composting the tops in order to minimize the risk of problems with asparagus rust. I will cover this problem later on, in the section on Pests and Other Problems.
Asparagus crowns have to be allowed to grow for two full growing seasons before you can harvest the spears. This will allow the plant to develop an adequate root system to produce the spears. Damage or harvest of the plants before two years could reduce yield for the overall life of the asparagus bed.
3. Caring for and Maintaining Your Asparagus
In this section, I will discuss a number of different aspects that are essential to how to grow asparagus that is healthy and survives the first couple of growing seasons. It is essential to pay careful attention to your asparagus plants during this timeframe. The first two years are when the plant is establishing and feeding its underground root system. That system is what will feed the asparagus spears in the third growth year, so making sure the root system is robust will be a very important aspect to how to grow asparagus. In this section I will cover fertilizing the asparagus bed, watering the asparagus, controlling for weed growth, and preventing and dealing with pests and disease, should they occur.
I described how to apply fertilizer to the asparagus bed during the first season in the “Planting Asparagus” section above. In the second season after you have planted the asparagus, you may reduce the amount of 5-10-10 fertilizer applied to the furrow by about half. In subsequent growing seasons, the asparagus bed can be fertilized in the same way that you apply fertilizer to the rest of the vegetable garden. I personally prefer to use organic manures and compost when fertilizing my garden, and you may choose to do the same. In my experience, building the soil with organic fertilizers and composts allows you to create a healthy, sustainable and nutrient rich vegetable garden that continues to produce robust yields year after year.
Asparagus plants do not generally need as much water as some other plants in your garden, but it can be important to make sure the soil they are growing in is kept adequately moist. The plants should be watered weekly so that the soil is moistened to a depth of about eight inches during the initial growing season. After the first year, the plants will have developed a rather extensive root system, and you can water them to a depth of about one inch per week, or two inches every two weeks, during dry weather. If you have regular rainfall during the second growing season, it will probably not be necessary to water your asparagus plants at all.
Due to the fact that learning how to grow asparagus is a rather long term project, problems with weeds can accumulate very quickly and overwhelm the plants. In addition, due to the fact that the crowns that produce the shoots usually tend to grow upwards, controlling for weeds using a hoe can inadvertently damage your plants. Some of the standard ways to deal with weeds that appear in asparagus beds is to use flame weeding, mulching, or other means other than herbicides to keep weeds away from the asparagus bed. The asparagus bed has to be kept free of weeds, and clean cultivation is better in order to reduce problems with asparagus rush and beetles.
Flame weeding is an organic technique of killing off weeds using a propane torch or blowtorch. Flame weeding is a useful technique for weeding when you are learning how to grow asparagus or other long-term vegetables. Simply pass the torch over weeds until the leaves begin to glow. It is not necessary to actually burn the weeds; heating them until they are glowing is enough heat to kill plant cells and denature the proteins in the plant’s leaf cells. Flame weeding (as compared to hoeing) has the advantage that it will not cut perennial weeds, allowing them to re-grow from underground shoots, and unlike hoeing, flame weeding will not cause you to inadvertently bring weed seedlings to the surface, where they could grow.
Grasses can be particularly invasive, so do not let any get close enough for them to drop seeds into the bed or send rhizomes underground into the asparagus patch. It is a good practice to apply between two inches and four inches of compost to the bed every year, and then cover that layer with a couple of inches of clean straw to smother any weeds. Of course, you should also pull any weeds that still manage to grow while they are still young and before they produce seeds. As always, be sure to remove the entire weed plant, including the root system, to make sure that it does not continue to grow after you have removed part of it.
Asparagus can be vulnerable to a number of root rot diseases, but these are generally not likely to appear if you situate your garden bed as I described earlier. Asparagus can also be affected by different molds that are spread by grasses, but properly controlling for weeds should prevent this from happening. There are also a number of viral diseases that can kill off your asparagus crop. It is generally believed that viral diseases are spread to asparagus by aphids, but they are generally very rare if you are simply learning how to grow asparagus in your backyard garden, as opposed to farms and commercial operations were acres upon acres of asparagus are being grown.
Asparagus rust is a common fungal disease that can plague asparagus crops in the East Coast and Midwest, as well as in cooler areas of California. Water or dew left on the plant for a period of more than ten hours can provide optimal conditions for the disease to spread. You can generally avoid asparagus rust simply by planting resistant cultivars. Beyond planting resistant cultivars, the best practice for how to grow asparagus that is not susceptible to disease is be sure to create a well drained raised bed, control weeds, and control aphids if and when they appear, and you will have no disease problems.
Controlling for pests is an important aspect of how to grow asparagus that survives through to the third year harvest. Aphids are best controlled through organic means. I always recommend preventative measures as the best cure for aphids and other pests, and one of the best preventative measures for aphids is to make sure your vegetable garden is fully stocked with a phalanx of predators that will feast on these pests. Lady bugs are readily available for ordering from online distributors, and should be released in your garden at dusk. They will patrol the garden for aphids as well as other pests, and will remain as long as you make sure the garden remains a hospitable place for them to live. This can be accomplished by planting flowers that attract lady bugs. Flowers that attract these tiny comrades include zinnia, marigolds, and yarrow. It can be a very good practice to plant these flowers throughout your garden and between rows of vegetables.
If you do find aphids on your asparagus plants – or anywhere in your vegetable garden, for that matter – simply wash them off the plants’ leaves using soapy water and a soft towel. The soapy water will not only help remove the aphids but kill them while you do so, and it will not hurt the plant in any way.
The asparagus beetle can be a serious pest to your plants. These are usually metallic black or blue and about a quarter of an inch long, although there are also some orange species as well. The adult beetle over-winters while dormant in organic material. It does not do well in very hot weather, and so it is not typically a serious problem in southern regions of the United States. The adult asparagus beetle does not do very much if any direct damage to the plants; as with most beetles, it is the offspring that are the main problem. The eggs, which appear like black specks on the base of the plant and undersides of the plant’s leaves, will hatch into gray worm like larvae that can be as long as one half inch in size. They will eat the leaves of the asparagus plant voraciously. The defoliation will weaken the plants considerably.
The best control of asparagus beetles is to cut down all of the asparagus foliage at the end of the season when it has turned yellow or brown and add it to your compost pile. This prevents the beetles from being able to over-winter near the asparagus patch. During the season, simply giving the foliage a good shake now and again will dislodge any larvae that are present. The larvae will be unable to climb back up the plant’s stalk, and will therefore become dehydrated and die in the soil.
4. Harvesting Asparagus
When the asparagus spears begin to emerge in the following spring, it’s when to harvest Asparagus. You should harvest all of them during roughly the same time frame, if possible. The spears should be between seven and ten inches in length at the time of harvest. You can either cut off the spears at the ground surface, or simply snapped off. With the exception of the cooler central valley regions of California, asparagus should be harvested for a two week period in the third year after planting the crowns; over a four week period in the fourth year after planting the crowns; and eight weeks every year thereafter. In the central valley regions of California, asparagus spears may be harvested for four weeks in the third year after planting the crowns; over eight weeks in the fourth year; and over twelve weeks every year thereafter.
If you are learning how to grow asparagus in order to harvest white spears, you should cover the asparagus row with a mound of soil that is eight to ten inches high in the early spring when the spears begin to emerge. When the spears begin to break through the top of the ridge of added soil, some of the soil can be removed from around the spear, and using a long kitchen knife, cut the spear about eight inches below the tip.
4a. Seed Saving
If you have grown female plants with the intention of collecting seeds, wait until the plant has produced berries that are ripe and bright red. Bring the seeds inside, and let them dry out on a paper plate or paper towel in a cool dry place. Because the berries are poisonous, it is a good idea to keep them on a higher shelf or cabinet that is out of reach of children and family pets. Once they have dried out, crush the berries and work out the seeds. Allow the seeds to dry, and place them in a labeled envelop for storage. Properly dried and stored asparagus seeds will keep for years.
4b. Saving Asparagus
You should eat your asparagus immediately, or else wash it and place it standing with the cut ends in about an inch of water if you wish to keep it in your refrigerator for a week or two. However if you have planted a very large asparagus bed, you may find that you have more asparagus than you can use or give away before it begins to spoil.
There are a number of ways to keep your asparagus for longer than a couple of weeks: you can blanch the asparagus by dropping it in boiling water for three minutes and then flash cooling it in ice water, and then either freeze or dehydrate it. Pickling is also a method that works quite well with asparagus. I don’t recommend pressure canning asparagus, but instead prefer to pickle asparagus in a strong vinegar brine, with mustard and dill for added flavor.
5. Final Word
I hope this guide on how to grow asparagus has been informative and fun to read. While asparagus does take a serious time commitment to produce edible stalks, it is not a terribly difficult plant to learn how to grow, and once you have succeeded in establishing it, it will reward you for years to come. In this guide we covered the biology, history and varieties of the plant, how to prepare the garden bed for planting, how to start from seeds as well as from crowns, how to maintain the bed once you have established the plants – especially during the critical first two years – and how to harvest and store your crop once it is mature. Best of luck now that you learned how to grow Asparagus!