by Linda Carloni, Master Gardener and ABG Board Member
For me the very best reason to plant asparagus is because it’s delicious. It also grows well here by the Bay, thriving in cool, humid summers.
Asparagus is a perennial plant, so you plant it one year and with luck it will produce harvests for up to 15 years in the same spot. It requires robust soil preparation and takes a bit of maintenance each year, but it is generally relatively carefree.
There are drawbacks. It requires patience – asparagus should not be harvested at all until the third spring after planting. Asparagus also takes a lot of space. Each plant needs an 18 inches square space, and each plant only produces a few spears. Given the deliciousness of asparagus, I think the patience and space is worth it, but it’s not for everyone.
In our area, asparagus is planted from January through March. Generally, gardeners use crowns (one year old roots); seeds are less expensive but can be tricky to get established. Crowns can be purchased at many nurseries. Consider varieties that are disease-resistant if you can find them. Plant asparagus in rich soil that has been well amended and is relatively weed-free.
To plant crowns, wait until the soil is dry enough to dig, and dig a trench a foot or so deep and about a foot wide. Make small mounds every 18 inches or so to create raised places for the crowns to sit on. Put down a few inches of compost or well-rotted manure over the bottom of the trench, including the mounds. Consider adding an additional slow-release fertilizer if your soil is sandy and drains of nutrients quickly. Put down another couple of inches of soil. Your objective is for the tops of the mounds to be around 6 inches below the soil surface at this point, so adjust your trench depth and level of compost/manure to achieve this. Place each crown on a mound, and cover with an inch or two of soil; level the trench at about 4 inches below the soil surface. Fill the trench in gradually as the plants grow bigger. The soil should be level with the rest of the surface by the next winter. (These directions assume you don’t have heavy clay soil, which requires a modified technique).
Keep the soil moist the whole first year. Keep the bed free of weeds. When the plants have come up well, you can mulch, which will help keep the weeds down. Apply a high-nitrogen fertilizer before the plants start to produce. Don’t cut the stalks for the first two springs, let them leaf out and become ferny. In the fall, the plants will die back; cut the stalks off at the soil surface after the plants turn brown. The third spring after planting, you can start to harvest, but only for two or three weeks. The fourth spring, you can harvest for 6 to 8 weeks, and in later years for 2 months, or until the largest spears become thinner than a pencil, whichever is sooner. In each year, stop at the required time and let the plants fern out. The ferns are supplying the roots with the nutrients they need to make next year’s sprouts, so leave them to flourish until they die back.
In early spring, before the sprouts shoot up, add a high nitrogen fertilizer such as hoof and horn meal, blood meal, or organic fertilizer blend made specifically for asparagus. Continue to keep the beds free of weeds. Asparagus is not particularly prone to pests in our region, but it is susceptible to fusarium, a soil fungus; rust, a fungus that attacks the above-ground parts of the plant, and a few insects. If your asparagus fails to thrive or you see pest damage, check for more information at: http://ipm.ucanr.edu/home-and-landscape/asparagus/
If you’ve got the space and the patience, with good soil amendment and a bit of care, asparagus crowns and a few years can yield tasty and healthy spring treats for you!