If you love asparagus and want to grow some yourself, waste no time in getting an asparagus bed planted. Even with the best of care, an asparagus bed won't hit its stride until several years after planting. Once it starts yielding a crop, the same bed will produce an abundant crop of spears spring after spring for at least the next 20 years.
In the old days, gardeners were told to prepare an asparagus bed by digging an 18" deep trench and then backfilling it with a mix of compost and soil. Today we can plant a strain of asparagus hybrids that are not only less work – the root crowns need only be planted 6" deep – these modern hybrids produce many more asparagus spears per plant. The production increases are due to the fact that the Jersey hybrids are all-male cultivars, so no energy is wasted producing seeds, and there are no weedy baby asparagus plants to compete with the mother plants. So forget about Martha Washington and the old varieties. Most of the new varieties are also resistant to the two common diseases of asparagus, fusarium rot and asparagus rust.
When planting a new asparagus bed, get rid of all the weeds and grasses first – even if this requires a full year of preparation. Asparagus crowns are usually available just once a year in early spring. So plan accordingly. Once the bed is weed-free, dig a trench about 6" deep and a foot wide. The crowns should be planted at 18" intervals, so put a shovel of compost and a cup of all-purpose, organic fertilizer in the trench every 18". Rock phosphate, a natural mineral powder, is another good addition. Phosphorus, which stimulates strong root growth, doesn't move through the soil as easily as other nutrients. You only get one opportunity to fortify the root zone, so don't miss your chance!
Mix the compost and fertilizer together with some garden soil and shape it into a little mound. Set the asparagus crown on top and drape the roots down around the sides. Cover the roots with garden soil and water well. As shoots appear, add more soil until the trench has been filled back to ground level.
Even though asparagus can sometimes be spotted growing in a ditch among thick grass, the domesticated varieties do not tolerate weed competition. No grasses, no weeds. So keep your asparagus bed well-mulched with leaves or straw. For the first couple years, weed often and carefully — the roots are near the surface, and can be damaged by weeding tools. Don't interplant other vegetables in the same bed. Asparagus hates competition of any kind.
Originally asparagus grew in swamps and wet places, so be sure to keep your soil moist. You may wish to use a simple drip-irrigation system or soaker hoses if you live in a dry region. Watering is a key to success, especially the first few years.
To keep your asparagus bed productive, don't get greedy: The first year after planting roots just pick for two weeks — a few spears from each plant. Then increase to four weeks the next year, and six weeks after that. Pick too much, and your plants will not be able to develop the strong root system and energy reserves they'll need to produce an abundant crop of spears the following season.
Twenty-five plants asparagus plants will yield more than enough for a family of four.