Loam-Based Potting Mix
Also called soil-based potting mix, this is made from sterilized loam. It's often available in different recipes or strengths, ranging from formulations for seeds and cuttings to high-fertilizer formulations for long-term, large plants such as shrubs. Loam-based potting mix retains water and nutrients well. Start fertilizing potted plants after three months, when the nutrients run out.
- Different blends are formulated for different types of plants.
- Holds water well.
- Contains good supply of nutrients.
- Bags are heavy.
- Incorporates small quantities of peat.
- Variable quality. Check reviews of brands in the gardening press.
Peat-Based Potting Mix
Also known as loamless or soilless potting mix, peat-based potting mix includes multipurpose types for seeds and general potting, and is best for short term, one-season displays. It is lightweight and well aerated, and the lack of nutrients is easily overcome by the use of slow-release fertilizers. When the peat dries out, it shrinks and can be difficult to rewet.
- Easy to handle, being light and clean.
- Consistent, reliable quality.
- Dries out quickly.
- Prone to waterlogging.
- Low nutrient levels.
- Plants need fertilizing after four weeks (seeds) or six weeks (plants).
Peat-Free Potting Mix
As concern about peat-stripped areas and ruined habitats grows, so the sales of peat-free potting mix have increased. One of the best, and least environmentally damaging, options is green waste compost. Made from recycled household waste, it is dark, black, and heavy, and suitable for most garden and potted plant needs. Otherwise, try coir, or composted bark (except for use with seeds and seedlings).
- Good nutrient levels.
- Retains moisture well.
- Heat treatment has eliminated pests, diseases, and weeds.
- Some peat-free potting mixes give better results than others with certain plants.
Made from shredded coconut husks, coir is sold either loose or in blocks; the latter need to be soaked for about 20 minutes before use. Since coir has no nutrients, it is generally mixed with multipurpose potting mix (one-third coir to two-thirds additional potting mix). Use it for annual displays in pots and containers where a light weight potting mix is needed, such as windowboxes and wall pots, or on balconies. It dries out quickly and plants will need to be watered frequently.
- Not entirely \"green\": peat-free, but it uses up thousands of air miles.
- Not for permanent displays.
- Plant performance can be variable.