Asparagus should be planted when the soil temperature is at or above 50 degrees. Planting in colder, wet soils could cause root rot. Generally, those in zones 7 and southward should plant in January and February, zones 5 and 6 should plant in March and April, while zone 4 dwellers should plant April and May. Check your gardening reference books or ask local nurserymen or agriculture office/extension agents to find the best time to plant in your area.
Make sure to soak the asparagus roots, whether just the crowns or transplants with foliage, in a liquid seaweed solution or other biostimulant rich in micronutrients like Great big plants or Garrett juice for about thirty minutes prior to planting. This will help prevent transplant shock and keep them moist until you have finished burying and mulching the bed.
Ideally, asparagus roots should be planted no more than 6 inches deep and 1-1/2 feet apart in the middle of bed rows that are 4-5 feet wide. Remember, if your soil drains poorly, you’ll need to plant your asparagus in raised beds with 6 to 8 inches composed of native soil and the appropriate amendments. If planting in raised beds, you’ll want to include the soil in the raised bed when measuring how deep to plant. In other words, plant your roots 6-8 inches deep from the surface of the raised beds. Going deeper — especially in clay — could be deadly.
If planting asparagus from transplants that already have foliage, plant them at the same depth as you would bare crowns. As they grow, cover their stems until the soil level is even with the rest of the beds. Be careful that you don’t drown the plants by letting the trench fill with water.
Place the asparagus in the trench or hole. Spread the roots gently, taking care not to break any stalks that might be trying to grow. There is no need to worry about which end of the asparagus is pointing up or down. Asparagus plants will grow and eventually right themselves if planted upside down.
Spread about a fourth of a cup of the appropriate phosphate fertilizer(see fertilizing), or a handful of soft phosphate around and on the asparagus crowns before they are covered with soil.
Cover the asparagus with soil up to the top of the bed. You do not need to slowly cover the plants as they emerge. Just cover them up all the way.
Apply a layer of mulch. It is important to keep your plants adequately mulched. Make sure you maintain around three to six inches of mulch over the entire bed, except when you have just planted your bed. Keep heavy mulch away from where the first shoots will be coming up or slugs, crickets or other pests could get the first spears. After they have emerged and begin to leaf out you can mulch almost (three inches away) up to the stems.
If you can find it, the best mulch is your local shredded tree trimmings, partially finished compost, decomposed leaves or decomposed hay.
You’ll want to stay away from Bermuda grass hay for mulch, unless it contains a mixture of other plants (clover, rye, or other forbs) and you know with certainty that it has not been sprayed with herbicide. Bermuda grass is often sprayed with very powerful, long lasting herbicides that can kill plants for years!
Water your plants in well with about one to two inches of water and then spray any liquid amendments over the planting area.
Protect your planting from pests and critters if needed. A large dog can really mess up a new asparagus bed. Fencing or thorny clippings usually work well for this. Whew, that was a long section, but if you followed it the asparagus should be set on the right track to a good harvest in two to three years.