If you have an established asparagus bed that's performing poorly due to overcrowding and you're looking for an intensive workout, look no further than dividing and transplanting the clumps. About the only thing that makes this job pleasant is that it's done during the cooler weather of fall, winter, or early spring, providing that the ground isn't frozen. Although the project involves preparing a site -- and sweating -- the end reward is a bountiful harvest of the long, green spears for years to come.
When to Divide and Transplant
Native to the Mediterranean and a herbaceous perennial in U.S. Department of Agriculture plant hardiness zones 2 through 8, asparagus (Asparagus officinalis) plants can produce their edible spears for up to 50 years if properly maintained. Over time, the clumps grow so thick that production decreases or stops, and the plants require thinning and transplanting. Established plants grow into clumps approximately 2 1/2 feet wide, so dividing them produces quite a few new transplants. Expect the loss of some crowns, though, due to unavoidable digging damage. For the best transplant success, wait for the plants to go dormant and naturally turn brown and die back before tackling the job. Asparagus that's divided and transplanted in fall and winter will give you an earlier harvest than plants transplanted in spring.
Asparagus has a tendency to escape cultivation and become invasive in some locations.
Conquer and Divide
The size of the mature clump and the soil it's growing in are the deciding factors in how difficult the dividing and transplanting job will be. Sandy soil is not as compacted as heavier soils like clay, so digging out the clump isn't as strenuous. Regardless of soil type, expect a mass of tangled roots and a bit more difficulty dividing larger, more established asparagus clumps. Using the proper tools and following a few basic steps ensure less damage to the crowns, which resemble small buds and produce the edible spears, and the pencil-sized roots you want to retain.
Things You'll Need
Spade or shovel
Inspect the asparagus clump before digging to locate the crowns in the mass of dead, brown stems and flowers. Knowing approximately where to dig helps you limit damage to the crowns and roots.
Search for the outer edge of the clump's root system using a garden fork. Poke the fork into the ground approximately 6 to 12 inches out from the mass of dead plant material, working gently around the clump to prevent excessive damage. Once you find the outer edge of the root system, use a shovel to dig all the way around the clump, creating a trench. Dig deeply enough to expose the entire root system, which is probably about the depth of the shovel's blade but could be deeper.
Continue digging under the clump to release the roots from the planting site. Try to salvage as much of the root system as possible without chopping into it or damaging the crowns. Lift the clump out of the soil using the garden fork.
If the clump doesn't come out easily using the garden fork, gently pry it out of the ground using a mattock or crowbar. Work the mattock or crowbar under the root system, prying it loose from the soil and avoiding cutting into the main portion of roots or crowns. Lift the clump from the planting site.
Rinse soil-covered roots using a garden hose. Rinsing with water causes less root damage than shaking the soil off, and you can then inspect the clump to find out where to separate it into multiple crowns. Gently pull the crowns apart, keeping their thick roots attached. You may have to sacrifice smaller crowns for larger ones when dividing a mass of intertwined roots.
Planting the Transplants
Asparagus is relatively forgiving of soil conditions as long as the soil is well-drained and weed-free and the bed is in a sunny location. Remember that the plants will grow in their new bed for decades, so select a site that's out of the way of foot traffic and other gardening activities.
Asparagus prefers a soil pH of 6.5 to 7.5 and will perform poorly if the pH is 6.0 or below. You can test the soil before planting to determine the need for additional phosphorus and potassium and adjust the pH accordingly, or you can till a blend of 10-20-10 fertilizer into the planting site before planting the crowns.
Things You'll Need
10-20-10 fertilizer granules
Evenly distribute 2 pounds of 10-20-10 fertilizer granules over every 100 square feet of the new bed. Work the fertilizer into the top 6 inches of soil using a shovel or hard rake. Water the fertilizer into the soil.
Dig a trench that's no more than 6 inches deep and 12 to 18 inches wide for planting the asparagus crowns. Crowns planted too deeply have reduced yields.
Evenly distribute 2 pounds of 0-20-0 superphosphate over the bottom of the trench for every 50 feet of row. There's no need to work the product into the soil before planting the crowns, as it won't burn them.
Place the asparagus crowns faceup in the trench and gently spread out the roots. Space multiple transplants approximately 18 inches apart in rows that are 5 feet apart. Backfill the trench with soil, covering the crowns with approximately 2 inches. Keep the soil covering the crowns loose and noncompacted to encourage the emergence of spears. When planting is complete, water the bed thoroughly so the roots are saturated. If conditions are dry, add supplemental water approximately once each week.
Asparagus plants are drought-tolerant and usually get enough water from rainfall.
You can generally start harvesting the spears on a limited basis the season following planting.
For over 25 years, Joyce Starr has owned businesses dealing with landscape & design, lawn maintenance, specialty herbs and a garden center. She holds certificates in landscape design and xeriscaping. Starr shares her passion for nature in her writing, publishing articles on horticulture, outdoor recreation, travel as well as business.