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What you need:
  • Compost
  • Garden fork
  • Green sand and rock phosphate
  • Pruners
  • Shovel
  • Tarp
  • Weeding knife or trowel
Perennial borders benefit greatly from complete renovation every few years, especially where tenacious perennial weeds such as grasses have taken hold. This is best done in fall in warmer climates, or in spring in colder areas (USDA zone 6 or below).
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Prepare by laying out a tarp or plastic sheet along the border to be renovated. This minimizes the mess.
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Beginning at one end, carefully dig around and lift the first 4-5 clumps of perennials, working into the border. Avoid injuring the roots. Move the clumps to the tarp. Some perennials resent disturbance and should be left in place. Check a good reference source or your local nursery if you aren't sure.
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Once on the tarp, divide the clumps into more manageable sizes. How you do this depends on the type of perennial. Usually clumps are pried apart with a garden fork, snipped apart with pruners, or simply cut into sections with the blade of a shovel.
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Now, select the clumps to be returned to the border. Aim for one or more sections collectively about 15" in diameter per perennial. Use the newer growth around the outside of the clumps. Discard any portions with entrenched perennial weeds embedded in the crowns. Extras can be composted, given to friends, or donated to a charity plant sale.
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Next, turn your attention to the border. Dig out and remove all weeds, being sure to get the roots. Dig compost into the area just cleared, as much as three or more wheelbarrow loads.
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This is a good time to work in rock phosphate and green sand, slow release sources of phosphorous and potassium.
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Rake the border smooth, then reposition and plant your perennials. Water well and move on to the next section, working around trees, shrubs, and those few perennials that resent disturbance.