Asparagus is usually the first vegetable out of the garden in spring, in early May. If you’re already growing asparagus – lucky you! – because after planting, it’s two years until the first harvest. It is well worth the wait though, since harvesting can continue beyond one gardener’s lifetime.
While asparagus can be grown from seed, it is easier to plant dormant one- or two-year-old asparagus crowns. The crowns are planted deep in the soil. Dig a trench 10” deep and 12” wide and as long as you need to be able to space the crowns 1 ½ – 2’ apart. If you dig more than one trench, allow 4’ between them. Loosen the soil a few inches below the trench. Add an inch or two of compost. Mound the soil a couple inches high where you’ll place each crown and set the crown atop the mound, spreading the roots out and down the sides of the mound. Add soil to the trench until the crowns are covered by about 2” of soil.
As the asparagus spears begin growing, continue to fill in the trench with soil and compost until it is filled to ground level. At this time, placing a mulch around the spears will keep weeds down.
Do not cut any spears the first year. The spears will form into ferns by mid-to-late summer. Let them die down naturally and leave them in place until spring. Around Thanksgiving, consider adding a winter mulch of hay or shredded leaves to prevent the roots from frost heaving which can damage them.
The next spring, cut down the dried ferns, remove any mulch and add compost or organic fertilizer to the beds. Do not cut any spears the second year. Replace the mulch once the spears come up and keep the area weed-free.
Finally, two years after planting, you may begin harvest, but only for a few weeks. The next year and for many years to come you may harvest until July 1.
Harvesting is most easily done by snapping spears off at ground level. You can also use an asparagus knife to cut spears just below ground level. Choose spears that are about the diameter of your finger. Let pencil-thin or smaller spears uncut to form ferns.
There are several asparagus cultivars appropriate for Wisconsin gardens including ‘Jersey Giant,’ ‘Jersey King,’ ‘Jersey Knight,’ ‘Mary Washington,’ and ‘Purple Passion’ which produces purple spears. The three ‘Jersey’ hybrids are predominately male plants which tend to have higher yields than female plants.
The most common pest on asparagus is the asparagus beetle. They are metallic blue-black insects with three white or yellow spots and are just 1/4” long. They lay tiny black eggs on the stems, which can easily be removed by rubbing your fingers over them. If you miss the eggs, they will hatch into light gray or brown larvae with black heads and feet. They can be picked off, or for serious infestations, dusted or sprayed with rotenone.
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