University of Vermont
Department of Plant and Soil Science
Dr. Leonard Perry, Horticulture Professor
University of Vermont
Asparagus is a tasty perennial (comes back each year) vegetable that many
gardeners like to grow. While most vegetables produce later in the
season, asparagus produces its edible parts (stems) right up front early in
spring. Since an asparagus patch can produce for a dozen years or
more, it is more important than with most any other vegetable to make sure
you site it where it can stay, and to prepare the soil properly before
The site should be in full sun. Ideal is 8 hours or more of direct sun
a day, although plants will tolerate (but be less vigorous) with 4 to 8
hours of direct sun. If planting in an existing garden, avoid areas
where onion family crops were grown previously. If possible, avoid
planting near the edge of the garden where grass and weeds may invade.
The soil should be well-drained and weed-free. If you haven’t tested
the soil recently, do so with kits from your local Extension Service office
or home kits available at garden centers. The soil pH (acidity) should
be 6.5 to 7.5. If lower than this, which is often the case, you may
need to add some lime according to the test results.
Begin by digging a trench about 6 to 8 inches deep for the newer hybrids,
working in ample amounts of compost or composted manure both to the trench
and the soil you’ll use to backfill. Older heirlooms are best planted
about 12 inches deep. Asparagus plants are sold in spring as dormant
crowns—basically a mass of roots with some buds or eyes on top. Make
sure you plant while they are still dormant (not growing, about when
daffodils are blooming), and don’t plant ones whose roots are obviously
shriveled and dried out.
Spread these roots out in the trench with the tops, of course, facing
upwards. Space about 18 inches apart, as they will spread and like
lots of room. Cover with only 2 to 3 inches of soil, and water
well. As the shoots (spears) emerge, add a couple more inches of soil,
until eventually the trench is filled back in. Then mound the soil
slightly, so water doesn’t collect around plant bases during rains or
Keep watered if needed—if there isn’t an inch or so of rain a week—watering
deeply when you do water. Watering deeply once a week is better than
watering lightly every day.
Keep plants weeded. This includes any plants, including seedlings
produced from the red berries that some varieties (those that are “open
pollinated” and not all male) produce. Hand weeding is best, or make
sure not to damage the plant roots if using a hoe. Applying a straw
mulch after harvest can help reduce weeds and retain soil moisture.
There are not too many problems to watch for on asparagus. The
asparagus beetle can nibble on spears. Look for their dark eggs on the
surface of spears, and scrape any off. Reddish brown spots on spears
are likely the asparagus rust disease, which can be treated with
The first year don’t harvest any young spears, but let them grow to produce
the airy, fern-like shoots that will help plants establish. The second
year you can harvest a few spears on vigorous varieties. Harvest only 2 or 3
spears per plant, over a two week period.
The third year you can begin a full harvest, IF the average spear size is
pencil thickness. Once an asparagus bed is established, you can
harvest over four to eight weeks. In cool springs you may be
harvesting every 3 days. In a hot spring you may need to harvest
So what to harvest? Snap spears off at the soil level when they are 6
to 8 inches tall and the tips are still tightly closed. If you won’t
be using them right away, cut the spears just below the soil level so they
have some of the white, woody base. This will help them remain fresh
for a few days and lose less water. Place spears in an inch or so of
water, upright, in the refrigerator. Or, you can soak in cold water a
few minutes, then drain and store in the refrigerator in plastic bags.
They will keep for about a week.
Don’t keep harvesting all spears all season, as they need some to form the
tops that will produce the food for the plant to remain healthy, and grow
well the next season. Stop harvest when new spears are skinny, and
spear tips turn feathery—loose and open. This is often about the time
you start to harvest peas.
Add 3- to 5-inches of compost over and around plants when you finish
harvest. Asparagus are heavy feeders since they need to produce enough
shoots for us, for themselves, and to live from year to year. If you
use an organic fertilizer in addition, or instead of as much compost, use
one with high levels of nitrogen (the first of the three numbers in the
analysis on the bag), and moderate levels of phosphorus and potassium.
At the end of the season, cut back the tops when they turn brown and
brittle. Topdress another 3 inches or so of compost or rotted manure
over plants, then several inches of straw over this. Use weed-free
straw, not hay which often contains weed seeds. The first will help
enrich the soil for the following season, while the latter will help protect
the plants over winter.
One of the standard heirloom varieties that has been around a while but is
still good, and is rust resistant, is Mary Washington. A similar one
is Martha Washington. There are several hybrids from Rutgers
University that produce many thick, tender spears and are disease
resistant. Look for Jersey Giant, Jersey Knight, or Jersey
Supreme. Purple Passion and Pacific Purple have, as the names
indicate, purple spears. The former has 20 percent more sugar than
green varieties. The purple will change to green when cooked.
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