Growing asparagus in home gardens
A quick guide to asparagus
- An asparagus plant can last 15 years. Choose its spot in the garden carefully.
- You can start asparagus from seed or from one-year-old roots, called “crowns.”
- Crowns grow vertically and horizontally. Planting at the right depth is important.
- Good soil moisture is important at planting for good root and fern growth.
- Begin harvest two years after planting crowns, three years after planting seeds.
- Harvest spears until June 30, and then allow the large feathery ferns to develop.
Asparagus is a sign of spring
Asparagus (Asparagus officinalis) is one of the earliest harvested vegetables each spring. Asparagus spears are crisp, tender and flavorful.
Asparagus is a perennial plant that comes back from the same root system every year. It needs the rest period that freezing winters provide.
The edible part of the plant is the shoot, or spear, that emerges from the soil. Later in the summer, these shoots will develop into tall plants with fine leaves or ferns.
The fern creates energy that will be stored in the underground portion of the plant to produce the following year’s spears. It is important to take care of the ferns even after the harvest is over to make sure you will have good future harvests.
Soil pH and fertility
- Have your soil tested
- Once you have planted the asparagus bed, it is best to test the soil approximately every three years and follow test recommendations. the autumn before planting. Add fertilizer based on soil test results for a good harvest.
- Asparagus grows best in soils with pH of 6.5 to 7.0, and does not tolerate extreme acid soils.
- Typical garden fertilizer rate for asparagus is 1 to 1.5 pounds (10-10-10) per 100 square feet before planting.
- If your soil tests high in phosphorus, use a low phosphorus (such as 32-3-10, 27-3-3, or 25-3-12) or no phosphorus (such as 30-0-10 or 24-0-15) fertilizer at the rate of ½ pound per 100 square feet.
- Continuous use of high phosphorus fertilizer such as 10-10-10 or 15-30-15, or high rates of manure or compost results in phosphorus buildup in the soil.
- Some runoff may occur. It can then become a major pollution concern in our lakes, rivers and streams.
- In the second and third years after planting, you can apply well-rotted manure, compost or fertilizer in the spring before spear development, and again as the soil warms up.
- Add the fertilizer alongside the row of plants, and scratch it in lightly, without allowing your tool to penetrate the soil more than an inch deep, to avoid harming the underground portions of the plants.
- Apply compost or aged manure alongside the plants as a mulch.
- After the asparagus planting is established, do not worry about adding fertilizer until after harvest, because the root system can store large amounts of nutrients.
- Do not use any fertilizer containing a weed killer ("Weed and Feed"), as it may kill your vegetable plants.
- There are female plants and male plants. This means the plants are dioecious.
- All produce edible spears.
- Only plants with all female flowers produce red, inedible berries in summer.
- Female plants grow larger spears.
- Male plants grow a greater number of smaller, uniform spears.
- Most hybrids, such as Jersey Giant, are plants with only male flowers that produce no seeds.
- Plants with all male flowers do not use energy on developing seeds and fruits.
- Male asparagus plants tend to live longer and produce more spears.
- Female plants can produce undesirable weedy seedling asparagus plants.
- The “Washington” series (Mary, Martha and Waltham)
- The “Jersey” series (Giant, Knight, Prince) can die at -30° F if there is not enough snow cover
- Viking KB-3, an open-pollinated variety
A planting of asparagus can last 15 years or more, so choose the spot for an asparagus bed carefully.
Choose a fertile, sunny, well-drained site with soil that holds moisture well.
Late spring frosts can kill emerged spears, so find an area that is not low-lying or exposed to frost.
Asparagus plants have deep root systems. Avoid areas with shallow soils, or soils prone to water-saturation.
If the asparagus bed is to be part of a larger vegetable garden, the best place is at the north end of the garden, so that the tall ferns do not shade the other crops.
Choose an area of the garden as a nursery bed. Young asparagus plants will grow here for their first year. The site for the asparagus nursery should be level and have sandy soil.
Plant seed in spring, about one inch deep, spaced two to three inches apart, within rows that are a foot apart. Seeds can take three weeks to germinate.
Keep the nursery bed free from weeds, as the asparagus seedlings will not be able to compete with strong weed growth.
Mulch the nursery bed with four to six inches of straw in late October to keep it warm during winter.
In early April, before the plants start to grow, dig up the crowns with as much of the root system as you can, and move them to their permanent location, following the method described below for planting crowns.
Most people start asparagus from purchased crowns because it is easier, and you grow a crop at least one year earlier than if planting seeds. Purchase one-year-old crowns. Older crowns are more prone to damage during transplanting.
- Dig a trench six to eight inches deep and wide. Set the crowns in it with buds upward and roots down. Spread the roots out in the trench.
- Space the crowns 12 to 18 inches apart and the rows four feet apart. The plants will fill in the space as they grow. Crowded asparagus plants are more vulnerable to fungal diseases including rust, purple spot and crown rot.
- Cover the crowns with two inches of soil.
- Right after planting, firm the soil, and water.
- As the shoots emerge, continue to fill the trench with soil without completely burying the new shoots, an inch or two at a time. By the end of the first growing season, the trench will be full.
Asparagus crowns will continue to grow both vertically and horizontally over several years. Planting at the right depth is important. Planting too shallowly could result in early spear emergence in the spring, increasing risk of freeze damage and winterkill of the crown. Starting with deeply set plants will help the planting live a long time.
How to keep your asparagus plants healthy and productive
Soil moisture is important for good root and fern growth. Established beds need plenty of water during the summer. Asparagus plants will not show signs of drought stress, so use extra care to make sure that there is enough water during the growing season.
If the planting does not receive at least one inch of rain weekly, soak the soil at least once a week. If your soil is sandy, it is important to water more often than once a week. An inch of water will wet a sandy soil to a depth of ten inches, a heavy clay soil to six inches.
Get rid of all perennial weeds before planting crowns. Get rid of annual weeds by digging shallowly with a hoe or hand tool, and by adding three to four inches of mulch on top of beds. Do not till or hoe soil more than three to four inches deep to avoid damaging feeder roots.
If perennial weeds begin to infest the asparagus bed, a good time to dig them out is in late fall after the frost has killed all of the ferns. Be careful not to dig too deeply, and try to leave the ferns in place. They will catch and hold snow on the bed, warming the crowns.
If female plants set fruit, each red berry can contain up to eight seeds. Volunteer asparagus plants can become the worst weed in the asparagus bed, so remove ferny seedlings.
The most common insect pests on asparagus in Minnesota are the common and spotted asparagus beetles. They damage asparagus by feeding on the spears, resulting in browning and scarring. Their feeding can also cause asparagus shoots to bend over making them look like a shepherd’s crook.
- Common diseases of asparagus include Fusarium crown rot, asparagus rust, and Stemphylium purple spot.
- Use good cultural control practices to reduce disease problems.
- Asparagus rust causes yellow and rusty orange spots to form on asparagus stems after harvest.
- Purple spot causes sunken purple spots on asparagus spears, and tan spots with a purple border on mature stems.
- Plants suffering from crown rot have poor growth. Leaves and stems may yellow and die back. When cut open, infected crowns are brown and decayed. The varieties Viking KB-3, Jersey Giant, Jersey Knight, and other members of the Jersey line tolerate crown rot.
- For assistance in diagnosing unknown problems, visit the University of Minnesota Extension diagnostic site “What’s wrong with my plant?”
In spring, spears will start to emerge from the soil. The first spring, a year after planting the crowns, do not harvest any spears. Allow the spears to become ferns and build the strength of the crowns.
The second spring after planting crowns, if the plants were strong and healthy during the previous growing season, begin to harvest when the spears are six to eight inches long. In the first year of harvest, only pick asparagus for two weeks. After that, allow the spears to develop into ferns.
In the following years, harvest asparagus up to July 1. Some gardeners will not harvest during the second year at all, preferring to allow the plants to build more strength before finally beginning to harvest in the third year.
- Fresh asparagus is such a springtime treat that you can eat it within hours of picking, but it can also keep for up to a week in the refrigerator. Put them in a plastic bag in the crisper drawer.
- You can freeze an asparagus harvest.
- You should only can asparagus if you can process it in a pressure canner.
Reviewed in 2018