Learning how to plant, grow and harvest asparagus can yield decades of tasty homegrown goodness. Asparagus is a long-lived perennial vegetable that, once planted, provides a hefty return on investment. A well-established and tended bed will produce an annual harvest that lasts between six to eight weeks and the plants will remain productive for 20 years or more. Asparagus is one of the first vegetables that can be harvested in the spring. It enjoys cooler climates, making asparagus an ideal vegetable for growing in USDA zones 4 through 6.
Asparagus Plants Like to Grow in Organic-rich Soil
Asparagus plants love a slightly acidic (pH between 5.8 and 7.0), well-drained loam. States such as New Jersey, Michigan, and northern Indiana are blessed with soil of this type naturally; gardeners in other areas may have to do a little work to optimize their growing area before planting asparagus. To prepare an asparagus bed, incorporate copious quantities of compost and well-rotted manure. If the soil tends to be alkaline, add in some peat moss and composted coffee grounds or tea leaves. Those with heavy soils may choose to create raised beds for their asparagus.
How to Choose Which Asparagus Variety to Grow
Choose an asparagus variety that is best for your culinary needs and that works well in your location. Rutgers University has developed a series of “super male” asparagus varieties, all of which have the word “Jersey” in their name. The crowns are primarily male, show a lot of hybrid vigor, produce 35% to 50% more than straight-run crowns from heirloom varieties and are relatively immune to fusarium wilt, which is one of the only problems that plagues asparagus.
Asparagus plants are dioecious, which means that some plants are male, and some are female. In general, it is preferable to grow male plants for the best spear production. The female plants flower and later produce red berries that contain the seeds. While female plants do produce spears, male plants don’t produce seeds, so they are able to put more of the plant’s energy into the production of spears; resulting in a larger harvest. Male asparagus plants also start producing spears earlier in the spring.
Another downside of female plants is that if you allow the seeds to drop and sprout, you risk having many volunteer seedlings popping up around your garden. If you are growing hybrid plants it is unlikely that the seedlings will be true to the original variety so they are in that sense they become weeds that will compete with your preferred plants for water and nutrients.
There are also purple varieties of asparagus available. Purple asparagus contains anthocyanin, a natural colorant and potent antioxidant and anti-inflammatory. Purple asparagus is also sweeter than the traditional green type and the spears stay tender even when they grow long and thick. Purple types can be eaten raw in salads or used for crudites with dip.
How to Plant Asparagus Crowns and When to Plant
Asparagus plants are composed of three parts: the fern (leaves), the crown (buds) and the root. Asparagus buds are the part that grow into succulent stems. Asparagus is best planted in the spring, four to six weeks before the last frost date.
How Long does it take to Grow Asparagus from Crowns
The fastest route to getting a crop is to plant asparagus crowns that are one year old. These are generally sold in lots of 25, which should provide enough to harvest for an average household. Plants grown from crowns should produce a viable crop after two years. Purchasing crowns also allows you to select a variety that is best suited for your area and your preferences.
How to Plant Asparagus from Seed
A longer route to an asparagus bed is to plant asparagus from seed. While this is less expensive at the outset, there are some drawbacks. First, the plants won’t be productive for at least three years. Second, you may end up with more female plants. While females produce larger spears, they produce fewer of them since most of their energy goes into producing seeds. Male plants produce more spears that tend to be consistent in size. In addition, seed-grown plants may not grow true to the original variety. Most gardeners prefer planting the crowns of a named variety and often choose batches that are primarily composed of male plants.
Planting an Asparagus Bed
An asparagus bed needs to be roomy and receive at least eight hours of sunlight daily. The soil should be well turned to a depth of 12 inches. Asparagus crowns are planted 8 inches deep in rows that are 10 inches wide. There is a top and bottom to an asparagus crown; the buds look like small nodules on top of the crown, and the roots hang down. Crowns should be planted bud side up, 18 inches apart in the rows. Spread the roots outward within the trench, then cover the crowns with 6 inches of very loose soil.
As the stems emerge, continue to backfill with soil until the ground is level. Once the rows are filled in, top with one to two inches of mulch to keep weeds at bay.
Fertilizing Asparagus Plants
Asparagus plants love to eat. It is recommended that the bed be top-dressed with compost once a year, and fertilized with a nitrogen-rich fertilizer in the spring just as the first spears emerge. To maintain plant vigor, allow stems that have not been harvested to grow into ferns. The ferns will continue to nourish the plants over the summer, and they have some ornamental appeal as well.
If there are female plants in the rows that produce berries, these can be removed before they ripen so the plant’s energy will be directed into feeding the crowns. This also prevents birds from eating and scattering those seeds hither and yon, so there won’t be stray asparagus plants in the flower beds or front yard.
When and How to Harvest Asparagus Spears
Asparagus spears will usually appear in early spring, depending on local temperatures you may see them pop up as early as March or as late as May and the annual harvest lasts between six to eight weeks.
Asparagus is very easy to harvest. Manually snap the spears off near the base when they are six to eight inches tall. A tender spear will snap easily; older spears will become woody and will need to be cut with a sharp knife or garden shears. Once the spears are over 12 inches tall, allow them to turn into ferns. These will be much too stringy to eat.
Once harvested, prepare the stalks by removing the tough ends of the stem. Use the fresh spears in stir fry dishes, grill or broil them, or steam them and serve buttered or covered with hollandaise sauce. Asparagus can also be frozen or pickled.
Fun Asparagus Trivia
- Asparagus was brought to North America in the 1600s by colonists.
- Michigan, New Jersey and California are the top asparagus producing states in the US
- Asparagus was considered to be an aphrodisiac by the ancient Romans. While it may not serve that purpose, it does contain vitamins A, K, folic acid and potassium, making it great for heart and eye health.
- Asparagus is also high in fiber and is recommended for gut health by traditional and ayurvedic medical practitioners.
- One serving of asparagus (four spears) without butter, hollandaise or other add-ins contains a mere 13 calories.
- Anyone can turn “normal” asparagus into gourmet white asparagus by blocking out sunlight as the spears emerge. Just throw a dark blanket or black fiber mulch cloth over the bed and tack the corners lightly. This prevents sunlight from reaching the emerging spears, so there is no chlorophyll produced. Check the spears periodically as they emerge, and harvest as usual. Remove the blanket once the spears are harvested to allow the ferns to develop normally.
This recipe for Asparagus and Pesto Pasta Salad makes a nice cold dish to eat on a busy spring day.