Planting mix for containers (Google Alert / The Union)

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Google Alert – gardening

The Union – Nevada County Local News

Container gardening: Soil is king

By Carolyn Singer
» More from Carolyn Singer
12:01 a.m. PT Aug 18, 2007

Early in the summer, the deer discovered the choice selection of plants on my porch. Gone was the beautiful white Impatiens in a blue container. In the same meal, my cherished red Begonia and scarlet pineapple sage (Salvia elegans) also disappeared. I should know better. This is not the first summer the deer have enjoyed my container gardening efforts in what I thought was my “safety zone.” But gardeners are ever optimistic, and I am no exception. Fortunately, this year I also decided to use hanging baskets for a few plants. So far, the deer have decided it is not worth it to climb onto the porch (three steps), climb up on my wicker chairs and stretch to reach those choice morsels hanging over the porch railing.
One of the containers I am particularly enjoying this summer is a combination of white Impatiens and perennial Lamium maculatum ‘Pink Chablis.’ The Lamium is a hardy evergreen, so when frost kills the Impatiens, the hanging planter will still be attractive for winter.

At this stage I’m wondering if the Lamium, which is deer-resistant, is actually hiding the Impatiens. I did observe a deer looking up at the container and could only wonder what she might be thinking.

Planting mix for containers must address the needs of the particular plant. A plant needing good drainage (Sedum or Lavandula) will suffer in a mix catering to the need for quick growth in rich soil (most annual flowers and vegetables).

Similarly, a very young plant, such as a recently rooted cutting, may not survive in a planting mix that is very fertile.

I like to make my own mixes. I begin with a combination that is two parts mushroom compost to one part rice hulls. When a pile is delivered, I wet it thoroughly. A few days later, I dig into it and use a simple hand test to check for heat. Sometimes it takes a few weeks for the pile to cool. When it has, nitrogen is not as active, and the chance of damaging young plants has lessened.

One of my propagation students from a few years ago recently told me a sad story about her plants. She used a bag of potting mix, and all the young starts died. This mix may have been too high in nitrogen. If you purchase a bag of mix, wet it, and use the hand test to check for warmth.

Into five gallons of the compost base, I add four cups of organic phosphorus and one cup of oyster shell. Perlite is then added for aeration and drainage. Low-irrigation plants need more perlite, and high-irrigation plants need less. Vermiculite is the next amendment, with more used for plants expecting rich soil, and less for those preferring lean. Using a five-pound coffee can, add one measure of perlite and two measures of vermiculite per five gallons of compost for plants that need richer and moister soil. Reverse those measures for plants that prefer less water and fertility.

I add native clay soil to the mix only when I am growing plants in very large containers.

My container mix must be good. After five weeks in the protection and high humidity of my cold frame, the pineapple sage and Impatiens have recovered from the deer damage. And where are they? Back on my porch, of course. I am an optimist.


Carolyn Singer has gardened in Nevada County for 29 years. She is the owner of Foothill Cottage Gardens ( Send your garden questions and comments to

Published by

Willem Van Cotthem

Honorary Professor of Botany, University of Ghent (Belgium). Scientific Consultant for Desertification and Sustainable Development.

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