Asparagus thrives in well-drained soils that get full sun for at least six hours per day. It’s important to note that asparagus can grow in a variety of soils — from sandy loam to clay. But, the area you select must be well-drained and prepared correctly (see bed preparation below).
Planting asparagus in poorly drained soil — especially poorly drained clay — would be the equivalent of flushing several twenty-dollar bills or more (depending on the size of your crop) down the commode. (Unfortunately, I have personal experience in this area that I’d rather not share.) Imagine spending hundreds of dollars on a properly laid out bed of good quality asparagus plants and the appropriate compost, amendments, mulch, etc. only to lose your asparagus – along with hours of hard work – to the pitfalls of poorly drained soil.
You must check drainage — both internal soil drainage and surface runoff — to make sure your beds don’t get wet feet. Surface drainage is rather straight forward. Simply don’t place the beds in a sinking or low-lying area, or where excess water runoff occurs during a rain. If you can’t plant anywhere else, plant in raised or mounded beds. Then, create trenches to divert the excess water away from your plants.
Internal drainage is a little trickier to deal with and test. For this test, make sure the area you’re testing is moist. If it isn’t, water the area as you would water a fully planted garden bed (or until the soil is moist to about one-foot deep). The next day, dig a hole (or several) about one-foot deep in the areas where your asparagus is to be planted and fill each hole with water. Check the next day to see if the water in the holes has drained away. If the water is gone, especially in clay soil, your drainage should be just fine for asparagus beds. If water is still standing in the hole, you will more than likely need to create a raised bed.
You will need to use your own judgment to determine whether or not the water test was accurate. For example, if your region is experiencing extreme drought or unusual weather conditions, your soil may have drained faster (or not drained as fast) as it would have in normal conditions.
Important asparagus culture info — A unique concern with asparagus is that it accumulates the heavy metal arsenic. Asparagus has an affinity for arsenic and adds it to its growing tissue, usually in such small quantities that it is actually good for you. Just enough arsenic is good for the heart, but too much is dangerous. You only need be concerned if the area you’re considering for planting has come into contact with CCA (chromated copper arsenate) treated lumber. A few wood shavings or scrap pieces of CCA-treated lumber left near the asparagus bed site should not be a problem. However, large amounts (a shovel full or two) of CCA sawdust or scrap pieces spread or buried near your asparagus beds could make your asparagus poisonous.
Another, far lesser problem is arsenic accumulation in old cotton fields. The cotton crops of old were sprayed with calcium arsenate, and the residue is still hanging around. This should not be a problem unless there was a significant concentration where you placed your asparagus plants.
Bed preparation, planting and cultural requirements
Remember when your parents and teachers told you time and again that patience is a virtue? Well, you’ll definitely need to heed that advice if you plan to be an asparagus grower! It can take up to three years to produce a decent harvest of asparagus spears, even when you select plants older than 1 year, which is not recommended. Adequate bed preparation will go a long way toward ensuring a timely and successful harvest. Likewise, cutting corners will almost certainly lead to profound regret
Planting asparagus in well-drained, raised beds in trenches no deeper than six inches works best. The beds can be prepared for the asparagus several months before you set out the plants. You will have to add more fertilizer at planting time when you plant asparagus in beds that have been sitting around for awhile.
To prepare your beds for planting, a test of your soil’s fertility and pH is essential. It will help you determine which additives, and how much of each, your bed requires. One of the more interesting aspects of asparagus culture is its fondness for soil that is near neutral or alkaline (high pH), not acidic. Soils with an acid pH of less than 6.5 can stunt — or even kill — asparagus. If your soil is too acidic, you’ll need to apply the appropriate amount of lime as indicated by your soil test. If your soil is alkaline, you may still need to apply an appropriate amount of sulfur, Epsom salts or products high in micronutrients like seaweed and Garrett juice.
Buying and applying amendments should be based on what your soil test results recommend. Soft or colloidal phosphate is good for just about any soil type and can be spread right onto the crowns during planting to give them a boost. Don’t forget to apply all of the needed nutrients, not just a few. Asparagus tends to like phosphate, but just because it likes more phosphorous doesn’t mean it can live without the other nutrients. Always apply some nitrogen, potassium, and other micronutrients, (see below for good fertilizer choices) preferably organic.
The area in which the amendments should be applied in the asparagus bed should be about 4- 5 feet wide and at least 5 feet in length for two plants, adding about 1 1/2 feet of bed length for every plant added. There should be at least 1 1/2 feet of bed after the last plant at each end of the asparagus bed.
It’s important to note that you should not remove your native soil and fill with other material. This can cause a sink that will fill with water and cause root rot. Also, you shouldn’t add a foreign type of soil to your bed or furrows (e.g., sand to clay or clay to sand). This can pack the soil or create a sink for water to collect. Use only native or a similar type of soil to raise your bed.
If the soil is very acid (below 5.5), an application of lime tilled into the area around the asparagus bed would help prevent the growing roots from reaching acid soil. Adding 3 to 6 inches of well decomposed compost, manure or other similar organic matter is the first thing you should apply to any asparagus bed. Commercial producers don’t always do this but it is definitely beneficial.
It is usually best to make the compost yourself, but your local garden center will sell it by the bag. You may want to research the best ways to produce compost before buying a system – otherwise, you may end up with supplies that are ill-suited to your needs.
You’ll want to avoid manure from auction barns or other places where animals could have eaten bermuda hay sprayed with Graizon, Picloran, or 2-4-D. Believe it or not, potent herbicides can pass through an animals digestive track and last for years in the soil! More important, they can be fatal to your asparagus. Dairy manure is often a safe choice, just be sure.
Do not till organic matter down deeper than eight inches, especially in clay soil. This can cause bad decomposition and produce things dangerous to your plants, not to mention its also a lot of back-breaking labor that you don’t need.
Cornmeal, especially horticultural grade cornmeal, is a good amendment for asparagus because there is lots of evidence that it kills Fusarium, the disease that causes rot in asparagus. Apply it at the rate of 20 lbs per 1,000 square foot of bed area.
Adding a product that contains Mycorrhizal fungus such as Garden-ville Mycorrhizal fungi, can help your asparagus absorb phosphate and protect it from diseases.
Once you’ve assembled and applied the appropriate additives, they should be tilled around 6-8 inches deep into the native soil or raised bed.
The bed is now ready for the asparagus.