During March and April avid gardeners are busy planting seeds to produce plants for their upcoming outdoor gardens. To achieve success, use of correct materials is essential and no other single material is quite as important as the planting medium in which the seeds are planted. All else will be in vain if a suitable planting medium is not used and the seedlings will in all likelihood not thrive. There are many possible media from which to choose; here are some of the most common:
Often called coir, this material is made from the hairy outer layer of coconuts. It is aged a couple of years and shredded to the correct consistency. It has a good pH level, good water retention, and is one alternative to peat moss since it is a renewable resource. Like peat moss, it would have to be mixed with other materials to produce a medium with good drainage and aeration.
The white material seen in many mixes, perlite is made from naturally occurring volcanic rock that expands and pops when heated. This is a good inert material which does not break down easily when included in a mix so it provides excellent aeration and drainage. Many gardeners use it alone as a starting medium for slips and cuttings.
Used for decades in planting mixes, peat moss has great water retention, with the ability to absorb from 10 to 20 times its weight in water. It improves the texture of a planting medium and is relatively lightweight. The down side of using peat-based products is that peat is considered a non-renewable resource, although methods of harvesting have improved in recent years to make the industry more sustainable.
Soilless peat-based mixes
By far the most popular planting media, these mixes vary from very fine for seedling to coarser mixes for general potting use. They contain some perlite to improve aeration and drainage, an organic wetting agent to allow the dry mix to absorb water, and dolomite lime to provide adequate pH to ensure optimum fertilizer availability. Some mixes also contain myccorhizae, natural pathogens which assist in fertilizer uptake and root health, as well as a starter fertilizer. Peat also contains a natural fungicide which will decrease the occurrence of diseases such as damping off.
Sand is heavy and because of its small particles, it can reduce the aeration and drainage in a mix because it fills in the voids within the mix. Care must be taken when using sand as a planting medium by itself because it does have a high water retention rate although the top layer will lose its water quite quickly. It is therefore used as a medium for cuttings but not often used for seeding. Some plants, cacti and succulents for example, prefer a soil mix which contains a good proportion of sand.
Ordinary garden soil Unl ike the other media
mentioned, garden soil contains pathogens which, when used indoors, may attack seedlings or the seeds themselves. It should be sterilized before being used as a seedling medium. Garden soil is usually heavy and does not have adequate drainage or aeration for this purpose. Many garden soils also contain clay and therefore become hard over time when used in containers. A bit of garden soil can be added to a mix to give it some body or to improve the texture of the medium, but it should not be used alone.
– Albert Parsons writes from Minnedosa, Manitoba