How to Grow Asparagus for Decades-Long Harvests

Asparagus is one of the best options for cold-climate gardeners interested in growing perennial vegetables. Most people – and mainstream plant retailers – have never heard of the perennial vegetables that grow in cold climates. You might be hard pressed to find American groundnut tubers or Good King Henry seeds but it’s easy to find asparagus cultivars and accompanying recipes and friends to use them up. Plus, asparagus prefers cooler climates and will continue to produce an abundance of delicious spears for up to 30 years.

Growing Asparagus – Basic Facts

Asparagus is hardy in USDA Zones 2 to 8. It prefers areas with alternating warm and cold weather – they tend to struggle in warm climates with mild winters. A period of cold weather or drought causes it to transfer its resources to the crown and root system. The plant can then produce healthy shoots in spring.

Perennial vegetables take much longer than annuals to establish, and in the case of asparagus you will need to wait until the third year after planting to harvest. During the first two years, the plant needs all the resources it can get to develop a large robust root system that will survive both two months of harvesting and a cold winter. Two years seems like a long time to wait but at least you won’t need to go through the hassle of starting and babying new seedlings each year. Once established, asparagus will be productive for at least 15 years. The perennial nature of asparagus also leads to high yields – a mere 100 square foot bed of asparagus can produce roughly 10 pounds per season.

Best Asparagus Cultivars

Asparagus growers are spoiled for choice – many cultivars with different colors, flavors and yields have been developed over time. It’s important to select the right variety since asparagus is a perennial that produces for many years.

Asparagus generally comes in three colors: white, purple and the traditional green. White asparagus is said to be milder, nuttier, and more tender than green. It’s extremely popular in Europe and its rarity is reflected in its hefty price tag. White asparagus is any green asparagus cultivar that’s been grown without light (blanched) so that the stems can’t produce chlorophyll.  Purple asparagus, on the other hand, is a completely different variety, though it’s planted and grown the same as green asparagus. Purple asparagus is milder, sweeter, and less fibrous than the green variety. Popular cultivars include ‘Purple Passion’, ‘Sweet Purple’ and ‘Pacific Purple’.

The purple color comes from a health-promoting antioxidant called anthocyanin. Purple asparagus loses most of its color during cooking, so people tend to steam it lightly rather than boil or roast it. Barely cooking purple asparagus is possible because the stalks are less woody than green asparagus.

Most people grow green asparagus because it’s the most varied and readily available. The all-male (or nearly all-male) varieties are preferred because they’re higher yielding. The all-male Jersey’ varieties, including ‘Jersey Giant’, ‘Jersey Knight’, and ‘Jersey Supreme’ were massively popular, though they’ve been outcompeted in the agricultural sector by the even higher-yielding, longer-lived and extremely cold hardy ‘Guelph Millennium’. In fact, the Jersey series has been discontinued this year. ‘Millennium’ is ideal for very cold climates because it dies back earlier in the fall and comes up later in the spring – avoiding frost damage – but still has up to twice the yield of other cold-hardy varieties.

The older, so-called heirloom varieties such as ‘Mary Washington’, ‘Connover’s Colossal’, and ‘Precoce D’Argenteuil’ produce both male and female plants. The yields are lower, with more random spear sizes, but asparagus connoisseurs grow them for their flavor or to harvest seeds.

Gardeners in southern zones shouldn’t give up on asparagus – there are cultivars specifically bred for warmer climates, like ‘Atlas’, ‘Apollo’, ‘De Paoli’, and the highly productive ‘UC157’. Researchers and growers have even found ways to trick the plants into die back and dormancy like they would in colder climates.

How and Where to Plant Asparagus

Asparagus can be started from one-year-old crowns or seeds. Most gardeners opt for crowns because plants grown from crowns can be harvested sooner (after two years) than plants grown from seed (three years).

The location of your asparagus plants is extremely important because they’ll be growing there for at least 15 years. If you pick the wrong spot you might have to re-plant and miss out on precious harvests. Asparagus should be grown in full sun, with over six hours of direct light per day in the growing season. Asparagus can still grow in part shade, though the plants will grow less vigorously.

Aim for a spot with moist, rich, well-drained soil. Pooling water makes the roots rot, so if you don’t have a good spot then you might have to make do with raised beds. Ideally, the soil should be amended with organic matter (e.g. compost or manure) before planting. All weeds (including grass) should be removed as they significantly reduce yields. Generous mulching will keep the weeds away and the soil moist.

Asparagus should be planted in late winter to early spring, as soon as the ground warms up. Crowns should be planted 12 to 18 inches apart and 4-6 inches deep, either in a trench or in small holes.

Some varieties can be grown from seed. After soaking for 2 hours, seeds can be planted in spring, 4 inches deep and 12 to 18 in inches apart in a row in a temporary spot. During the fall you can transplant the male plants to the bed where they’ll remain for the next decade or so. Alternatively, you can start them in small pots (planted ½ inch deep) before transplanting to the permanent bed. Transplanting must take place after the last spring frost.

The best way to start any seed is with my baggy method as explained in this video.

Asparagus Maintenance

Besides weeding, fertilizing after harvesting, and adding new mulch and compost when necessary, there isn’t much work to be done in asparagus beds. Asparagus requires about an inch of water per week. A few hours of moderate to heavy rain in a week saves you from having to water them.

A thick layer of mulch over the crowns protects them during winter. Mulch can be moved away temporarily in spring to warm up the soil and make spears emerge faster.

Asparagus ferns can be cut back in early winter after they’ve wilted and turned brown.

How and When to Harvest Asparagus

Asparagus can be harvested in the spring of the third year if you planted crowns, or the fourth year if you planted seeds. When the spears are 8 to 10 inches tall, simply cut off the stalk with a knife or scissors close to the ground. Tender purple or white stalks can often just be snapped off by hand. During the first year you can harvest for 2 to 3 weeks, gradually increasing after a couple of years to a maximum of 2 months. After consistent harvesting, the shoots will get progressively thinner (about the width of a pencil). At this point, stop harvesting. A few shoots must be left behind to develop into fine, fluffy leaves called “asparagus ferns” – this structure will die back and feed the crowns for next year’s harvest.

All the work and waiting will be well worth it when you get pounds of fresh spears each spring. Happy asparagus plants grow unbelievably fast (up to 1 centimeter an hour). Some farmers claim they can see the stalks slowly stretching towards the sky on perfect, warm afternoons.

Other Perennial Vegetables

Here is an article that discusses several other perennial vegetables, 10 Perennial Vegetables for Colder Climates.

Written by: Marika Li