The Key to Success; Good Potting Soil and Good Fertilizer

A good potting soil can be defined as follows:

“A good soil must be light when dry, properly retain water (neither too much nor too little), have a pH of between 6 and 7, as well as support and nourish the plant”.

A great definition however, how do we actually judge the quality of a good potting soil?

To do this, it is necessary to take into account several elements. :

  • The mixture must be porous
  • It must contain ingredients in various dimensions
  • Be aerated
  • With coarser ingredients in sufficient number
  • It must retain water well when wet and not become compacted as a result of repeated watering
  • Its pH should be between 6 and 7
  • With nutrients in sufficient quantity to nourish the plants

These last two elements can only identified through laboratory analysis.

What ingredients?

The vast majority of blends are primarily composed of peat moss, along with black earth, coconut fiber dust and composted conifer bark.

It also contains a good deal of compost (from garden or kitchen waste, manure, marine residues or mushroom substrate), and at times vermicompost. Depending on the product, one can also find dolomitic lime, coarse sand, perlite, horticultural vermiculite and gypsum. Some manufacturers add mycorrhizae.

The ingredients are indicated on the bag, which allows you to know the composition. In general, they are listed in order of importance, with the most important appearing first on the list.


Black earth currently sold in bags is not a good potting soil for container gardening. It doesn’t contain any nutrients; it dries up quickly, and has a hard time retaining water. Avoid it at all cost…despite its price!


For growing vegetables in pots, there are two types.

Natural fertilizers can be plant based: compost, seaweed in liquid form, seaweed meal and wood ash. Those that are animal based have fish emulsions, blood meal, chicken manure, composted manure and shrimp, crab or fish meal. Basalt, mineral phosphate powder and Sul-Po-Mag are mineral based.

With the exception of the liquid form algae, these fertilizers are added to the soil at the beginning of the season or sprinkled over it during the season. The frequency and quantity used vary according to the needs of the plants and the concentration of the product. There are so-called complete products that combine several ingredients in the correct proportions.

Controlled release synthetic fertilizers are embedded in a polymer or resin to control their release. As a result the fertilizer is available when plants need it. These fertilizers are added to the soil only once at the beginning of the season.

Bertrand Dumont, horticulturist, author and speaker

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