Edible of the month: Asparagus

Mature asparagus plants send up multiple spears that can be cut for up to 6 weeks.

Asparagus (Asparagus officinalis) is a member of the lily family and has been grown and eaten since 1000AD. It’s thought to have originated in the eastern Mediterranean region as a wild plant and modern varieties have been selected for larger and tastier spears. Asparagus is unique, because, unlike most home garden vegetables, it is a perennial, coming back year after year. A well-maintained asparagus bed can produce spears for 20 years. Therefore, it’s important to spend extra time and energy preparing the soil in the bed and planting it correctly.

The young shoots (spears) are what we eat. The spears are only available in spring for a 6- to 8-week period. (There has been some experimenting with forcing asparagus to send up new spears in summer and fall, too. See the article link later on). Once the asparagus spears are allowed to grow into ferns, they can top 6-feet tall, making a beautiful barrier or wall of green in your garden. Asparagus can be used as an edible hedge, backdrop to flowers or shrubs, or a visual barrier. The ferns turn yellow in fall and should be cut back to the ground in winter.

Asparagus is a great spring treat steamed, roasted, or sautéed in butter and garlic, or served along with other spring vegetables such as peas, spinach, and spring potatoes. It’s high in fiber, vitamins A and C, and minerals, such as iron.

Cut asparagus spears at the ground level with a sharp knife.

Planning

Asparagus is a hardy (USDA zone 4), cool- loving crop that sends spears out of the ground when soil temperatures are above 50 degrees F. Since asparagus evolved around a salty sea, it likes a well-drained, slightly alkaline soil. One key to selecting the right variety of asparagus is making sure you get one adapted to your soil and climate conditions. The other is to choose a variety that is predominately male. Asparagus plants are either male or female, that is, male and female flowers are produced on separate plants. The females produce red berries in summer. The flowering and fruiting reduces the amount and size of spear production. Another problem with female asparagus plants is the berries drop and germinate in the row creating many small asparagus plants. These can overcrowd an asparagus bed and become weeds.

Breeders have created “all-male” hybrid varieties which are mostly male. They produce up to 3 times more asparagus spears and fewer berries than older, open pollinated varieties that are a mix of males and females. Many of these all-male hybrid varieties come from research done at Rutgers University so they often have “Jersey” in their name.

Here are some of the best asparagus varieties to try. They are best purchased as 1-year old crowns for spring planting. Asparagus seed is not widely available and takes longer to produce mature plants.

‘Jersey Knight’ – One of the best performing Jersey hybrid varieties, it’s a vigorous plant that’s resistant to rust, crown rot, and fusarium wilt. It is especially adapted to growing in clay soils and in warmer climates.

‘Jersey Giant’ – One of the first in varieties the Jersey series, this hybrid is best adapted to colder climates and produces spears 7 to 10 days before ‘Jersey Knight’.

‘Jersey Supreme’ – The latest variety in the series this variety produces more uniform-sized spears and is earlier than previous Jersey hybrids. The plants are disease- resistant and best adapted to lighter, sandier soils.

‘Purple Passion’ – This uniquely-colored asparagus is widely adapted and produces purple colored spears that fade in color when cooked.

‘UC 157’- This California hybrid is adapted to warmer climates with mild winters and produces high yields of uniform spears. It does have some female plants.

‘Viking KB3’ – An open pollinated variety that has a mix of male and female plants. It is a better producer than the traditional ‘Martha Washington’ open- pollinated variety.

Asparagus beetle adults attack young spears and older ferns reducing yields.

Preparation

Choose a sunny, well-drained site with neutral to slightly alkaline soil. Since this is a perennial crop, it’s important to remove weeds and amend the soil well. It’s easier to amend the soil now than trying to do it after the asparagus is growing. Till the soil and dig a trench 1-foot deep and as long as you desire. Each crown can produce 1/2 pound of spears when mature. For most families, you can estimate planting 15 to 20 crowns per person with crowns spaced 18 inches apart.

Planting

Plant outdoors 2 weeks before all danger of frost has passed and soils have dried out. Backfill the trench with 4 to 6 inches of finished compost and soil mixed evenly together. Form 4- to 6-inch high, volcano-like mounds with the compost every 18 inches in the trench and lay the spider-like crowns and roots over the mounds. Drape the roots evenly on all sides of the mound with the crown sitting on the top. Cover the crowns with soil and backfill the trench as the spears grown with more soil until the trench is filled and crowns are buried 3 inches deep.

Care

Another key to growing asparagus is keeping the bed well weeded. Be careful using a hoe when weeding since the crowns are not deeply planted below the soil surface. Some people have taken advantage of asparagus’ tolerance to salt and spread salt on the bed to kill weeds. However, this practice is not recommended because eventually the soil gets too salty for even the asparagus plants. Fertilize the bed every spring with compost or a balanced organic fertilizer, such as 5-5-5. Keep the bed well watered and mulched with a 2- to 4-inch thick layer of bark mulch.

‘Purple Passion’ is an attractive ornamental, as well as edible, asparagus variety.

Asparagus has a few pests. Diseases such as rust and wilt can attack the crowns. Select disease resistant varieties and be sure the soil is well drained to avoid these problems. Asparagus beetles will attack the spears and ferns. These small, bright red beetles emerge as asparagus spears start growing in spring. They feed on the spear tips and eventually lay eggs on the ferns. The eggs hatch into soft-bodied gray grubs that continue to feed on the fern fronds. Their feeding can defoliate the ferns and reduce the energy sent back into the roots, weakening the crown and lowering production. Control the asparagus beetles by hand squishing the adults and spraying the grubs with neem oil or Spinosad organic sprays.

Let the ferns naturally yellow in fall. Cut them down and remove them in winter to reduce populations of overwintering insects and diseases.

Harvest

It’s important not get over eager in harvesting your asparagus spears. The first year after planting don’t harvest any spears: let them all grow into ferns. This will strengthen the crown for higher future production. The second year after planting harvest only those spears that are larger than a pencil’s diameter for 2 weeks in spring. The third year you can begin harvesting all spears larger than a pencil’s diameter for 6 to 8 weeks in spring.

Start harvesting as soon as large enough spears emerge from the soil by snapping off the spears with your hand at the soil line when they are 6 to 8 inches tall.