Choosing your sowing substrate

The choice of substrate is a crucial element for sowing! The quality of the substrate is among the primary factors influencing seed germination. Humidity, light, and temperature also play a significant role. What are the characteristics of a seedling substrate? A good substrate has properties that allow for both rapid and healthy seedling growth. Water retention capacity: Water is essential for germination! The seed becomes waterlogged and swells. Gradually, the seed coats soften, and the first root, called a radicle, appears. Next come the cotyledons and leaves. The substrate must therefore be able to retain a large amount of water and remain moist throughout the growing period to ensure sufficient water nutrition for the plant. Porosity and drainage: Excess water is very dangerous for seeds! Just like roots and leaves, they need oxygen to live and grow. Overwatering will fill all the air spaces (porosity) in the soil, suffocating the seed and rootlets. A substrate that retains too much water will have the same consequences. The affected seedling will gradually wilt and decompose. Very humid environments are also conducive to the development of pathogenic bacteria and fungi. Young seedlings are fragile and particularly susceptible to "damping-off," which affects the roots and crown. Choose a potting soil that drains well enough to limit the appearance of diseases. Generally, "special seedling" potting soils contain river sand, perlite, or other materials that ensure good drainage. Density and particle size: The seeds will need light soil to allow the very first root to emerge and develop. The aerial part will also have to find its way to the light. Pieces of bark or clods will be obstacles that are difficult for young organs to avoid, which is why the grain size of a seedling substrate must be fine to allow their development. Quantity of nutrients: The fertility of the substrate depends on the quantity of nutrients it contains. As they grow, the seedlings draw on their own reserves but they also extract the minerals they need from their substrate. Potting soils are generally enriched with nutrients by adding fertilizers to stimulate their development. A substrate free of diseases and weeds: Naturally, a substrate contains thousands of bacteria and fungi! Not all of them are beneficial for young seedlings. Commercially available bags have been previously sterilized to avoid any risk of disease. Buying seedling soil Seedling soils are more expensive than universal soils but, as their names indicate, they are suitable for sowing. Universal potting soil is often heavier and composed of coarser materials that can hinder the development of young roots and the aerial part. The majority of substrates sold are composed of 30 to 90% peat. Due to the disastrous impact of its extraction on ecosystems, the use of peat should be reduced in the coming years. Be aware that a single centimeter of peat takes about ten years to be regenerated! There are now universal and special seedling soils labeled "peat-free", choose them, they offer the same properties. Make your own seedling soil You can also choose to make your own seedling soil by getting as close as possible to the ideal properties mentioned above. Try with 40% garden soil, 40% compost made from bark, wood fiber or mature green waste and 20% sand. Sift the mixture if necessary. The proportions of garden soil, compost and sand will probably need to be modified depending on the type of soil in your garden.