Asparagus is one of the first plants that greets us in springtime! It’s a perennial, which means that once it gets established, the tender spears will return year after year. Here’s how to grow asparagus—from planting through harvest.
Thriving in areas with cool winters, asparagus is usually grown from 1-year-old plants or “crowns” (bought at a garden center) but it can also be grown from seed. Plant in early spring as soon as the soil can be worked.
Asparagus plants are either male or female. Female plants produce berries; males plants do not expend energy on berries so they can be up to three times more productive than female plants. For this reason, growing male asparagus plants is preferred.
If you are starting asparagus for the first time, we would plant 10 to 20 asparagus plants per person (15 to 30 feet of row).
How long does it take to grow asparagus?
Newly-planted asparagus plants may take 2 to 3 years to truly get started and produce, so patience is needed! But then again, the plant can be productive for 20 years or more, producing ½ pound of spears per foot of row in spring and early summer, so we think it’s definitely worth the wait.
After they’re established, however, asparagus are fairly fast producers, sending up new spears every few days for a few weeks in the spring.
When to plant asparagus
- Plant asparagus crowns in the early spring, as soon as the soil can be worked.
- Start seeds indoors in the late winter, following this method:
- Soak seeds in water for up to 24 hours before sowing.
- Sow seeds in moistened peat or seed-starting soil in flats or peat cups.
- Once plants reach 12 inches in height, harden them off outdoors for a week.
- After the last spring frost, transplant the young plants to a temporary garden bed. Once they mature in the fall, identify the berry-less male asparagus plants and transplant them to your permanent planting site, removing the less-productive female plants.
Choosing and preparing the planting site
- Given that asparagus is a perennial plant that comes back year after year in the same spot, it’s important to select a proper planting site where it will thrive.
- Before you do anything, check the pH of your soil. Asparagus thrives in slightly acidic soil (pH of about 6.5).
- Choose a site that has at least partial sun (full sun is not needed).
- Asparagus does not like to have its feet “wet,” so be sure that your planting site has good drainage and doesn’t get swamped by snowmelt in the spring.
- Eliminate all weeds from the planting site, digging it over and working in a 2- to 4-inch layer of compost, aged manure, or soil mix. (Learn more about soil amendments and preparing soil for planting.)
- The soil should be loosened to 12 to 15 inches in depth to allow the asparagus crowns to root properly and not be disrupted by rocks or other obstacles.
How to plant asparagus
- Plant crowns deeply to protect them from the cultivation needed for annual weed control.
- Dig a trench of about 12 to 18 inches wide and 6 to 8 inches deep. If digging more than one trench, space the trenches at least 3 feet apart.
- Soak the crowns briefly in lukewarm water before planting.
- Make a 2-inch-high ridge of soil along the center of the trench and place the asparagus crowns on top of the mound, spreading their roots out evenly.
- Within the trench, space asparagus crowns 12 to 18 inches apart (measured from root tip to root tip).
Once you get to this point, you can follow one of two planting methods: the traditional “little-by-little” method or the easier “all-at-once” method.
Once the trenches are dug and the crowns are set out:
- Cover the crowns with compost and topsoil, burying the crowns 2 inches deep. Water in.
- As the season progresses and spears grow to be 2 to 3 inches tall, add 2 more inches of soil to the trench, being careful not to bury the spears completely.
- Once the spears again grow through the layer of soil, add an additional 2-inch layer of soil. Repeat this process until the trench has been filled to ground level. Depending on how deep you dug your trench, you may need to add soil 1 to 2 more times throughout the season.
- After you’ve filled the trench completely, mound the soil slightly to prevent water from pooling around the emerging spears.
- Some gardeners simply fill in the trench with soil and compost all at once. While it’s thought that the traditional method results in stronger plants overall, gardeners don’t typically have any issues result from the “all-at-once” method, either. As long as the soil is fairly loose, the spears won’t have a problem pushing through to the surface.
How to grow asparagus
- When the trench is filled, add a 4- to 6-inch layer of mulch.
- Water regularly.
- Weed as needed, taking care not to disturb roots.
- Do not harvest the spears in the first year (the plant needs time to grow out its root system), but cut down dead foliage in late fall and side-dress with compost.
- During the second year, harvest for only 3 to 4 weeks, side-dressing with compost in spring and early fall and cutting down dead ferns in late fall. Keep the bed thickly mulched.
- During the third year, the bed should be in full production, so you can start to harvest asparagus sparingly throughout the season.
If you must move asparagus, transplant the crowns in early spring when they are dormant or late fall before the first fall frost (after foliage is cut back). Dig and lift crowns with a garden fork, being very careful not to disturb the roots. Divide the clump into two or more pieces. Water transplants. Do not harvest heavily in the following year.
|Asparagus beetles||Insect||Spears turn brown and bend in a hook shape; defoliation; damaged fruit/seeds||Remove beetles by hand; dispose of plant matter in the fall where eggs could be housed|
|Cutworms||Insect||Wilting; stems of young spears severed (“cut”) just above soil line||Watch for cutworms and remove by hand; clear away weeds and other plant matter. Find more cutworm prevention tips here.|
|Fusarium Crown Rot||Fungus||Yellow, stunted, wilted ferns; reddish-brown spots on lower stems, crowns, or roots; rotting spears||Destroy infected plants; avoid planting new asparagus nearby infected site for 5+ years; choose resistant varieties; disinfect tools to prevent spread; avoid overharvesting|
|Asparagus Rust||Fungus||Pale green spots on emerging spears become yellow/orange with concentric rings; reddish-brown blisters appear in summer, releasing rust-colored spores that turn black; brown ferns; defoliation; reduced vigor||Rust requires moisture to spread; avoid getting excess water on spears or ferns. Destroy infected plant matter; choose resistant varieties; ensure good air circulation; avoid planting new asparagus nearby|
How to harvest asparagus
- If you have young plants, the season may last 2 to 3 weeks. However, established plants produce longer—up to 8 weeks.
- Check your plant every other day for harvest-ready spears. Spears grow quickly and may become too woody before you know it! Once an asparagus spear starts to open and have foliage, it’s too tough for eating.
- Harvest spears when they reach 8 to 10 inches in height and between ½ and ¾ inch thick. (Bear in mind that younger, thinner spears will be more tender, so harvest according to your own taste.)
- To harvest asparagus, simply cut the spears with a sharp knife or scissors at ground level.
- Stop harvesting spears when the diameter of the spears decreases to the size of a pencil.
- After harvest, allow the ferns to grow and mature; this replenishes the nutrients for next year’s spear production. Always leave one or two spears.
- Cut back asparagus ferns AFTER the foliage has died back and turned brown or yellow. This is usually in the fall after a frost or two. Cut the ferns back to the ground.
How to store asparagus
- Asparagus does not keep for very long after it’s picked, so be sure to eat it within two or three days from harvest.
- Brush off any visible dirt or give the spears a light washing with cold water before storing. It’s very important to dry washed spears thoroughly; moisture can lead to mold.
- To store, bundle the spears together, wrap the stem ends of the spears in a moist paper towel, and place the bundle in a plastic bag. Store in the crisper drawer of your refrigerator.
- If you have enough space in your fridge, you can also store asparagus by placing the spears in a cup of water. Keep about an inch of clean water in the cup.
Note: Asparagus plants are either male or female. Female plants produce berries; males plants do not expend energy on berries so they are estimated to be up to three times more productive.
- For highest yields, plant male hybrids such as ‘Jersey Giant’, ‘Jersey King’, and ‘Jersey Knight’. Older varieties ‘Mary Washington’ and ‘Martha Washington’ may produce female plants, which are not as productive as the males.
- White asparagus is not a variety, but simply asparagus grown in the absence of sunlight to prevent chlorophyll from developing. White asparagus is slightly sweeter, but has less fiber than green asparagus.
- Purple asparagus is bred to be purple in color, but turns green when it is cooked. Purple varieties tend to have thicker spears, but fewer of them.