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If there’s any crop (and flavor) that says “spring,” it’s asparagus. Asparagus is one of the earliest vegetables you can harvest in springtime, and it only lasts about six to eight weeks. If you’re new to growing this perennial vegetable, it’s hard to know exactly when to plant asparagus. In addition to being harvested in the spring, it’s planted in the spring, as well. But timing is important.
The part of the plant you have come to know as the asparagus vegetable—the spear—is actually the succulent, immature stem. The stem emerges from buds on the roots of the plant. The root-and-bud system is called the crown. You can grow asparagus from either crowns or seeds. How and when to plant asparagus crowns differs from how and when to plant asparagus seeds.
Unharvested asparagus spears develop leaves and are called ferns. This part of the asparagus plant is both beautiful and useful. The ferns create energy to store in the crowns, which then produce next year’s asparagus crop.
This article covers why, how, and when to plant asparagus, as well as information about harvesting and caring for these plants so you can start your own asparagus patch at home.
Why you should grow asparagus
Asparagus is a sought-after Mediterranean vegetable at farmers’ markets, with many of us clamoring for this fleeting taste of springtime. While it may be available in grocery stores year-round, it’s hard to replace the flavor and texture of asparagus grown close to your plate.
There are a number of reasons why you might want to grow asparagus, including:
- This perennial crop requires little attention after it becomes established.
- Asparagus crowns can produce for 15 years or more.
- Asparagus ferns create an interesting backdrop for other garden areas.
- These vegetables are nutritious—they’re rich in Vitamin B, calcium, magnesium, zinc, and fiber.
Where to grow this perennial vegetable
As long-lasting perennials, asparagus plants can live for decades. Before you decide when to plant asparagus, you first need to decide where to plant it.
Asparagus has impressive root systems—possibly as large as 5 to 6 feet in diameter and 10 to 15 feet deep—so soil quality is especially important. Soil should be deep and rich in organic matter. Asparagus also needs soil with good drainage, as the roots can rot in areas prone to saturation. It prefers a soil pH of 6.5 to 6.8 with balanced nutrients.
Asparagus is a hardy spring vegetable, but it actually needs cold temperatures to go into dormancy. At the same time, asparagus spears are frost-tender upon emergence. Site your asparagus beds in an area that’s not low-lying or otherwise first to see frost.
Because the fronds can grow up to six feet tall, they can shade other crops. Plant asparagus on the north side of the garden to prevent shading.
Put your asparagus patch in full sun. Think about the trees and tall shrubs that are growing around the bed, as well. Because asparagus will be planted in its spot for decades, be sure it won’t be shaded out by the larger plants growing around it.
The importance of good timing
When to plant asparagus is always in springtime. It needs every bit of time in its first spring to get established before harvest. This is the hardest part about growing asparagus: You can watch the stems and foliage grow, but you cannot harvest asparagus spears until the third year after planting. The asparagus crowns are building up their energy reserves so they can produce spears for decades to come.
Two ways to plant asparagus
There are two ways to plant asparagus: by seeds or by one-year-old crowns. Planting by crown is a simpler method, but it’s possible to sow asparagus seeds. Sometimes it’s not possible to find the asparagus variety you want in crowns so you will have to plant by seed—or vice-versa.
Several asparagus varieties are commonly available as seeds and crowns. They can typically be shipped to you from growers with a climate similar to yours. Asparagus has been the subject of various breeding programs, and from them hybrid varieties with useful characteristics are now available to home gardeners.
Common asparagus varieties include:
- Jersey Supreme, a hybrid for early spring production
- Jersey Knight, a hybrid resistant to root rot, fusarium, and asparagus rust
- Jersey Giant, a male hybrid
- Mary Washington, an heirloom resistant to asparagus rust
- Purple Passion, a smoky-purple or blue-green hybrid that’s resistant to asparagus rust and root rot
You’ll notice white asparagus varieties are not on this list. White asparagus is not its own variety, rather it’s grown by blanching asparagus spears, growing them in complete darkness to prevent them from producing chlorophyll.
When to plant asparagus crowns
Exactly when to plant asparagus crowns depends on the timing of your spring weather. Plant as soon as the soil temperature reaches 60°F (15.5°C). Use a soil thermometer to keep track of soil temperature, as this differs from air temperature.
If purchasing crowns that must be shipped to you, try to time your delivery date to coincide with the date you expect to plant. Talk with asparagus growers, local seed suppliers that stock asparagus crowns, or your Cooperative Extension agent or master gardeners group to learn when gardeners in your area typically plant asparagus. Know that depending on the year’s weather, this date could differ.
How to plant asparagus crowns
Plant asparagus crown in furrows six to 12 inches deep. If you are planting multiple rows, space the furrows three feet apart. Leave the soil from your digging alongside the trench, as you’ll need to use it.
Add soil amendments to the trench, if you need them. A basic compost or 10-10-10 fertilizer—that’s equal parts nitrogen, phosphorus, and potassium—enriches the soil without adding too much of any one nutrient.
Place crowns in a line down the furrow, spacing the buds of the crowns 12 inches apart with the roots trailing behind, like a jellyfish. Push two to three inches of soil back into the trench to cover the crowns and roots. Water them in immediately.
In a few weeks, once the first spears are a few inches tall, add another two to three inches of soil. Do not fully bury the spears. Do this one more time, adding soil to cover the spears again so the crowns end up about six inches deep in the soil. Be careful to not break spears as you add the soil.
How and when to plant asparagus seeds
If you are looking for a challenge, are unable to find the asparagus crowns you want, or are looking for a more economical way to start asparagus, you can start asparagus from seed. While the process adds an extra step, when to plant asparagus seeds is the same as when to plant asparagus crowns: in the spring.
Start asparagus seeds in pots 6 to 8 weeks before your last expected frost—one plant per pot. Germination may take 3 weeks. When the soil reaches 60°F (15.5°C), transplant the asparagus crowns into a nursery bed. Follow the instructions above, except this time, cover the crowns with two to three inches of soil, and don’t cover them again.
Control the weeds in the nursery bed, as the fledgling crowns will not be able to compete with other plants. Mulch the new crowns well in the fall so they stay insulated during the winter. In early spring, before the plants start to grow, dig up the crowns with as much as the root system as possible, and move them to their permanent bed, again following the instructions above for planting asparagus crowns.
How long until harvest?
In the first and second springs, the asparagus ferns gather energy via photosynthesis and store it in the crowns. The plants need all the energy they can get during this time. In the third spring, you can harvest asparagus for two to three weeks, but allow the ferns to grow for the remainder of that season. Starting with the fourth spring, you can harvest for six to eight weeks, being sure to leave some ferns on the plants to continue replenishing the plants’ energy.
When it is time to harvest asparagus, get your shears ready. Spears can grow up to two inches per day. Start harvesting when they’re about the diameter of a pencil, six inches or taller.
Both male and female plants produce spears. The female plants produce fewer but larger shoots in the spring and inedible red berries in the summer. The seeds dropped from the berries may produce unwanted seedlings. The male plants live longer. They produce more but smaller shoots in the spring; no berries in the summer. Some hybrids are male varieties, not producing female plants at all. You may choose to plant only males or a combination of male plants and female plants.
Quick tips for growing asparagus
Consider these additional tips for growing the best asparagus possible:
- Consistent soil moisture during the harvest season may increase harvest yields and will help the crowns stay healthy for future years. Like much of your garden, your asparagus patch wants one inch of water per week.
- Weeding by hand is the best way to reduce competition for asparagus’s nutrients, water, and light. Deep cultivation can damage crowns and roots. If you choose to cultivate with a hand tool, stay within the top two inches of soil, and don’t hoe just before or while spears are emerging.
- Mulch will conserve water and protect crowns from the coldest temperatures. Consider planting a low-growing cover crop as a living mulch.
- Leave the ferns standing until they have gone completely dormant in the fall. As the ferns are dying, they transfer nutrients to the crowns. Pruning them too soon will reduce the yield next year and impact the health of the plants going forward. Learn about how to cut back asparagus.
- Test your soil every three years. Side-dress and shallowly scratch in amendments only as needed.
Once you master when to plant asparagus, prepare for a long and fruitful garden relationship ahead. You’ll come to look for these plants as a signal of springtime, with their delicate spears. Soon after, they’ll provide interest through the summer and fall with their playful fronds. Be sure to exercise patience in the harvest, and be diligent about weeding and watering. Read even more recommendations for growing great asparagus. The taste, nutrition, and ornamental benefits you receive will be worth the effort you put into establishing your asparagus patch.
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