Planting asparagus at the correct depth and spacing, in a very well-weeded bed, are among the critical factors for success with this delicious, perennial vegetable.
When initially planting asparagus, amend the bed or row with a lot of compost, preferably homemade if possible. Homemade compost ususally contains a much more diverse mix of ingredients, and therefore a broader range of nutrients, than the bagged kind from the store that is often just a mix of cow manure and wood chips.
It’s also a good idea to add a good dose of bone meal to the bottom of the hole or trench to provide the asparagus the phosphorus it needs to encourage excellent root growth.
Planting asparagus from seed will add a year of waiting and weeding onto the time it takes for your first harvest, so it is much better to start with crowns from a local nursery or seed catalog. See the article on Growing Asparagus for a discussion of all-male hybrids, which are among the highest yielding varieties.
If you’re a row gardener, allow yourself 4 or 5 feet between rows, because when the asparagus “ferns out” it will take a lot of space, and you need to be able to access the plants. Dig a furrow down the row that is 5 or 6” deep, and lay out the asparagus crowns at about 18” spacings.
Make sure the soil is loose and well composted, and then replace the soil in the trench over the asparagus crowns. Some folks recommend filling in the trench a couple of inches at a time over the course of a week or two, but I haven’t found this to make any difference. Just don’t walk where you’ve planted or you will compact the soil and make it harder for the asparagus to get started.
If you’re planting in raised beds, plant the asparagus crowns in 5-6” deep holes on 18” centers. Also make sure that you have removed any perennial weed roots before planting, because getting them out after the asparagus becomes established will be impossible.