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Gardening Answers Knowledgebase

Plant Answer Line Question

Keywords: Container plants, Potting soils, Container gardening

I am doing container gardening -- rather large plantings that will incorporate small trees and shrubs -- and therefore want a potting mix that will last longer than the usual for smaller containers, and will provide some nutrients. I just read about soil-based potting mix, but there is no further info in my text. Can you describe this, and tell me if it commercially available, or do gardeners mix up their own recipe?


There are a variety of opinions about soil-based potting mix. Taylor's Guide to Container Gardening (edited by Roger Holmes, Houghton Mifflin, 1995) provides a recipe for a "real soil" mix combining equal parts garden loam, compost or peat moss, and coarse sand. The sand should be as coarse as possible, and should not be able to pass through a window screen. According to the guide, "the success of any mix using soil depends on the soil's quality." For large pots and planters, the mix should be equal parts coarse, medium, and fine materials (from Landscaping with Container Plants, by Jim Wilson, Houghton Mifflin, 1990), for example:
Coarse material: small nuggets of pine or fir bark
Medium material: pulverized pine or fir bark
Fine material: moistened sphagnum peat moss

The National Sustainable Agriculture Information Service has extensive information on organic potting mixes.

Mother Earth News published an article by Barbara Pleasant in the December 2008/January 2009 issue entitled Make Your Own Potting Soil which should be helpful. The recipe includes pasteurized compost or soil.

Date 2016-12-07
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Plant Answer Line Question

Keywords: root pruning, Container plants

I'm interested in information about root pruning container plants. When and how? Do the plants have to be removed from the containers in order to do it? Do the cut roots need to be removed from the container too?


You will need to remove the container in order to prune the roots. Don't leave cut roots in the container.

Pruning expert Lee Reich demonstrates his root pruning technique in this Fine Gardening magazine video.

According to Sunset's Container Gardening (1998), fall is the best time to do this (when the plant is not in the height of the growing season). They suggest that a containerized plant can be root-pruned after 3 years or so. Here are the steps they recommend:

  • Loosen the soil around the pot walls with a knife.
  • Tap around the rim with a rubber mallet and then pull the plant free - OR:
  • float the root ball out by forcing water from a hose through the drainage hole
  • Examine the root ball and trim any twisted roots.
  • Pull out and untangle large roots, and then use shears or a pruning saw to cut big roots back by 1/3 to 1/2.
  • Scrub the inside of the pot with a stiff brush and plain hot water or a solution of 4 parts water to 1 part bleach. Rinse with clear water.
  • Repot with fresh potting mix.

Date 2016-09-24
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April 11 2017 13:50:16