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Question & Answer

We are discussing Gardening, Growing and Green Thumbs!
With Brian Walters, Diana O'Brien and Pauline Cornish

Question:
Do you have any tips for making your own potting mix? Some of the bags of growing medium sold commercially seem to dry out far too quickly for my needs and our garden soil doesn’t seem to encourage good growth.

Answer:
Diana - Soil alone is almost always unsuitable for use in containers. It will invariably pan quickly in pots that need to be watered frequently in warm climates, so that aeration becomes poor and root growth suffers.

However, by amending small quantities of good quality garden loam, or even omitting the soil altogether, you can prepare a mix dense enough to anchor the roots of a plant, provide ample moisture yet at the same time permit good drainage and aeration.

Many materials can be used in a recipe for a potting mix and quantities and types of ingredients are usually varied to suit particular plants. Succulents for example would need the free-draining properties of a basically sandy mix, while azaleas require the moist acid conditions that a greater percentage of coco-peat would provide.

Some suitable materials, which can all be purchased from major garden centres or landscapers, include pulverized bark, coco-peat, coarse washed river sand, composted sawdust, perlite, vermiculite and of course home made goodies like compost and leaf mould.

Since the advent of slow release fertilizers, the nutrients which used to be supplied by a soil based potting mix assume lesser importance but for home garden use in extra large containers and tubs which might be used for growing large shrubs or small trees, up to 20% of friable garden loam will help to increase stability of the root system as well as increasing the nutrient holding capacity.

Measured quantities of whatever materials you wish to use (a 4.5litre bucket is a useful size) can be placed on a large plastic sheet on the ground and thoroughly mixed with a spade. The mix can be stored in lidded containers for use as required but don’t add fertilisers at this stage. It is easier to judge the correct quantities required according to the size of the pot or container at planting time.

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