My wife and I just finished cleaning up and mulching the asparagus beds and I thought it was a good time to talk about how we grow asparagus. It is a popular but sometimes challenging vegetable for most gardeners to grow, and we often get questions about it. Questions like “how long do you harvest?” (usually for eight weeks) or “how long has it been planted?” (since 2007).
Folks also want to know what varieties we planted. We have one row each of Jersey Giant, Jersey Knight, and Jersey Supreme. All three are hybrids developed by the Rutgers Asparagus Breeding program. I have not really seen significant differences in how the three perform here.
And how long are those rows? They are 30 feet long, and 4 feet apart. How did I plant them? After roto-tilling the soil, I dug a shallow trench about six to eight inches deep, planted the crowns with roots spread out in all directions, and then covered with a little soil. I gradually filled in the trench as the spears started coming up, and I kept them well watered during that first year.
I always tell people that if you like to eat asparagus, planting it is an investment with great returns. A well-tended bed can bear for 25 or more years. We took small harvests from ours in 2009 and 2010, and then began harvesting for eight weeks in 2011. Our total harvested from the beds is now 165 pounds, including the 35 pounds we got this year. It is safe to say the plants have paid for themselves by now – and then some!
Once the plants are established, weed management is probably the biggest challenge. This year my wife got out before the spears started emerging and cut down the dead foliage from last year. This can be done any time after the foliage is thoroughly brown and dry, from late winter until early spring. Then she weeded the beds and mulched between the rows with a layer of cardboard covered with straw. We have also used newspaper in the past, though cardboard seems to do a better job of keeping down the weeds. Our experiment with landscape cloth did not work very well, as weeds came up through it too easily and getting them out was difficult. She also likes to spread shredded paper or newspaper down the rows where the spears come up. That’s the hardest part to keep weeded.
After the eight week harvest window, we weed and mulch the beds as soon as possible, which this year was a couple of weeks ago. Then we let the new spears grow into the ferns that will grow until freezing weather arrives, replenishing the roots and crowns for next year’s crop. As you can see in the below photo, we still need to weed a bit between the rows, and then add more straw. Once the ferns fill out, the foliage will form a canopy that will shade the beds and help keep down weeds.
Another question I often get is about fertilizing asparagus, which I do once a year. The general advice is either to do it in early spring before the spears emerge, or after the harvest is finished for the year. This year I applied the fertilizer in June as we were weeding and mulching the beds. I spread it down the center of each row where the crowns are located.
And how much fertilizer do you need to use? Of course that sort of depends on the type of soil you have and its fertility. The advice I have seen, including this bulletin from the University of Missouri Extension, generally says to add between .1 and .15 pounds of nitrogen annually per 100 square feet of growing area. Since our beds are about 360 square feet that would mean between .36 and .54 actual N. Asparagus also needs moderate amounts of phosphorus and potassium for good results, and since I know our soil is low in those two nutrients, I used a fertilizer mix that supplied NPK plus I added kelp meal for its many micro-nutrients.
The only real pest problem we have had with asparagus over the years is the asparagus beetle. Both the adults and their larvae feed on the spears and ferns. They can be controlled with hand picking the adults or with a pyrethrin spray if the outbreak is really bad. But we did something different this year that really helped with that problem. In past years we harvested only spears that were larger than 1/4 inch in diameter, at least as big around as a pencil. We left the smaller spears. This year we followed advice to cut all spears regardless of size. This had the benefit of keeping down the beetles, since they had very little to feed on during the harvest season when they are typically a problem. I’ll monitor the foliage throughout the summer to make sure they don’t get out of control then.
Asparagus is a delicious and nutritious perennial vegetable, and its tender spears are often one of the first harvests each spring. If you are thinking about growing it, a little planning and annual effort can lead to a crop that will keep on feeding you for years to come. I hope you have found this information useful, and I’ll be back soon with more happenings here at HA.
For more information about growing asparagus:
How To Grow Asparagus (Rodale’s Organic Life)
All About Growing Asparagus (Mother Earth News)