Seed Compost

To give your seeds the best chance of success, use a seed propagation compost; this is moisture retentive and has a fine texture that draws up moisture by capillary action right to the surface of the tray or pot.

As salts may damage seedlings, seed compost is low in nutrients. A standard seed mix contains 2 parts sterilised loam, 1 part peat substitute (or peat), and 1 part sand, with ground limestone and superphosphate of lime. It is advisable to buy a pre-mixed seed compost, as you can then be sure that the proportions are accurate.

Seed compost must be lightly firmed in the pot or tray using a presser board before the seeds are sowed. This will prevent the formation of air pockets, which would hinder the capillary action of moisture uptake. However, take care not to firm loam-based composts too much as some air is required around the roots for optimum plant growth.

Seed compost should be kept constantly moist, but not wet. If the growing medium becomes too wet, the amount of oxygen available to the roots will decrease, and the seedling may die or fall prey to disease.

Peat-Free Seed Compost

If you don't want to use composts with peat in them on environmental grounds, try an alternative such as coir seed and potting compost; however, you will have to be prepared to start feeding the young plants earlier. As these fibrous composts have increased water-holding capacities, you must take great care not to over-water; even when the surface is dry, the compost underneath may still be wet.

Cuttings Compost

Cuttings composts are designed for use in high-humidity environments and contain a high proportion of sand to promote efficient drainage. They are made up of one part peat or peat substitute and one part sand (or other free-draining substance such as perlite), plus a small amount of lime, calcium carbonate, dried blood, potassium nitrate and potassium sulphate.