Growing asparagus in the garden is a highly rewarding project -- albeit one that many people never think to consider -- if you have the patience and tenacity to do the prep work. Home grown asparagus tastes much better than store bought and doesn't typically have the woody stems if it's eaten quickly after harvest. Since it's one of the few garden plants that is a perennial, it will come back year after year!
The one drawback to planting asparagus, is that the plants will take a couple of years until they are fully mature. Until that point it's necessary to harvest lightly to keep the crowns productive. Most recommendations say to wait until the third harvest season to harvest the full crop; thankfully a good asparagus patch can produce for 25 years or more if you follow these tips.
1. Prepare garden bed
Carefully preparing an adequate garden bed is a crucial step in planting asparagus. Plants prefer full sun locations, and like to be grown in lighter soils that warm up quickly in the spring and drain well. For best results build a raised garden bed (DIY Network can walk you through the process) for your asparagus and work in plenty of aged compost or manure.
2. Remove all weeds and grasses
Make sure that all weeds and grasses are removed from the space before planting, since they are a fierce competitor with young asparagus shoots. If necessary you may have to spray the area with an herbicide and wait until the following season to plant.
3. Buy asparagus crowns
Asparagus can be planted from seed but it's a tricky endeavor. It's better to buy 1-year old crowns for planting and will be much more successful in the long run. Two-year old crowns tend to suffer more from transplant shock and won't produce a harvestable yield any quicker. Crowns are usually available for purchase in early spring. After purchasing, plant as soon as possible.
4. Plant in trenches
To plant the crowns, dig trenches about 6-8" deep and about 12" wide and scatter either all purpose fertilizer or rock phosphate at the bottom of the trench to encourage root growth. Rows should be at least 2' apart from each other. Space crowns in the trenches about 1 1/2 to 2' apart and cover to the top of the crowns with a mixture of soil and compost.
5. Backfill trenches
As the crowns grow and send up shoots, add a couple inches of the soil/compost mixture every couple of weeks until the trenches are completely filled in. You can even mound the soil up slightly to allow for settling that will occur over time.
6. Mulch the entire bed
After the trench has been completely filled in, and even mounded slightly, cover the entire area with a thick layer of mulch to help keep weeds down. Weed competition is especially tough on an asparagus crop, and will impact productivity considerably the first couple of growing seasons.
6. Water immature plants regularly
Until the asparagus patch is well established it's important to water regularly. The first couple of season keep the planting bed consistently moist but not overly soggy. Over time the maturing plants will crowd out weeds and send long-fleshy roots deep into the soil. As that happens watering will become less critical.
7. Fertilize in the spring and fall
Asparagus plants are heavy feeders and will grow best when fertilized in the spring and fall. Top-dress plants with a liquid fertilizer or apply a side-dressed all purpose granular fertilizer at the rate recommended on the product label. Backyard Vegetable Gardening has some great tips on fertilizing asparagus if you are interested in more information.
8. Allow stalks to grow in the fall
In order to encourage new growth for the following season, allow spears to develop naturally after the harvesting season has ended (typically in late spring or early summer). The unharvested spears will grow into lacy fronds and divert energy into the root system for a healthy crop the next season. When the fronds turn yellow cut them about 1" above the soil line to decrease disease and insects problems while overwintering.
9. Harvest when mature
Spears can be harvested when they reach 5 to 7" in height. The diameter has no bearing on the quality of the spears, or the harvest window. Snap spears off at the soil line before they begin to open and enjoy immediately or store in the refrigerator wrapped in plastic to keep them humid.