MASTER GARDENERS: Asparagus care in the off-season

There's nothing like starting the garden year with fresh asparagus straight out of the garden.

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There's nothing like starting the garden year with fresh asparagus straight out of the garden. Of course, I like the parsnips that were left unharvested from last year and the fruit-like rhubarb that follows, but the asparagus is a wonderful, early-season treat.

This may seem like the wrong time of year to think about asparagus; harvest season is over and the crowns are probably sold out. Now is a good time to plan and prepare the bed you will plant next year.

Asparagus can be started from seeds or purchased as started plants but I prefer to grow them from crowns. Crowns are the heart of the plant and grow deep underground. This depth will vary with soil texture and other growing conditions.

Start next year’s asparagus project by keeping your future bed fallow. This can be done with chemicals or by cultivating with a rotor tiller every two or three weeks. Rototilling gives you an opportunity to increase fertility with 10-10-10 fertilizer, animal manure or compost. Cultivating will discourage quack grass, kill the annual weeds and encourage more annual weeds to germinate which will be killed with the next cultivation. Covering with a tarp or ground cover will prevent new seeds from blowing in while depriving the existing weeds of light.

Asparagus prefers a soil pH of 6.5 to 7. It tolerates soil textures from sandy to clay. Organic matter is always a good thing.


Asparagus can be grown using hügelkultur principles by burying woody material under the bed. It can be grown in raised beds. If the raised beds are deep enough, you can incorporate the woody materials in the bottom of the raised bed.

The University of Minnesota recommends several varieties of asparagus including Millennium, Jersey, Washington, Viking and Purple Passion. Some nurseries offer all male plants. Male plants spend less time developing seeds and are expected to produce more from year to year. They also live longer. Female plants produce larger diameter spears. They produce red, inedible berries which result in baby plants in the bed. Uniform spears of one gender are easier to cook.

In spring, plant the crowns in the bottom of eight-inch trenches spaced three or more feet apart. The plants will spread out naturally. Within the trench, space the crowns a foot apart in the row. Cover with an inch of soil. As the plants grow taller and stronger, add soil until the row is level.

The university recommends harvesting two years after planting crowns and three years after planting seeds. I think this is optimistic. I will usually wait three years and pick for a short period of time to begin with. Pick asparagus when it looks ready to eat at about eight inches high. Pick thoroughly. When you stop, let the whole bed go into ferns. Mid- to late June is a good time to stop picking a mature bed.

Don’t neglect asparagus’s off-season when you are producing next year’s crop. Add more fertilizer and organic material and keep it watered. An inch a week is recommended and more on sandy soils.

If you have an old planting that is grown up in weeds and grass, asparagus has a good way to save it. In early spring after the grass greens up and before the asparagus comes up, you can apply a weed-killing chemical or you can cultivate with a rotor tiller down four inches and instantly clean the bed up. After a year of weed-free growth, the bed should be productive again.

These local garden articles will reach you each week throughout the gardening season, but gardening information can be found year-round by clicking on "Yard and Garden” at the University of Minnesota Extension website, , or by visiting our Facebook page at .

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