The perfect seed starting potting mix should be moisture retentive without being soggy, and not too rich in nutrients, which can harm sensitive seedlings. Here’s our ideal seed starting mix recipe:
2 parts sieved compost. The compost will release nutrients gradually, helping to feed seedlings as they develop.
2 parts coir (coconut fiber) or leaf mold. Rehydrate a block of coir by soaking it in water until it easily falls apart. Alternatively, use well-rotted leaf mold in place of the coir. The coir or leaf mold adds bulk to the seed mix and helps retain moisture.
1 part perlite or sand. Perlite will lighten the mix and improve its air content. If you prefer not to use perlite then you could substitute sand, but be aware that this will give a heavier mixture.
Mix all of the ingredients together thoroughly with your hands or a spade. Make up a batch and store it in a lidded container or in old potting soil sacks (or any other plastic sack) with the top rolled down and secured. Store it in a cool, dry place.
Moisten your seed starting mix before you use it, and then sow your seeds according to the packet instructions. Water carefully using a mister or a watering can fitted with a very fine rose. Alternatively, make a watering bottle by piercing holes into the cap of a plastic bottle using a pin.
Many seedlings need potting on into larger containers at least once before transplanting them into their final position. You can use the same potting mix, but hungry seedlings such as tomatoes will appreciate the addition of worm compost or slow-release fertilizer.
Container Potting Mix
Annual crops: Use 2 parts compost and one part leaf mold or coir. Add 2-3 generous handfuls of perlite for every 10 gallons of mix, plus a similar quantity of worm compost for hungry plants. If you don’t have access to worm compost, use a slow-release fertilizer instead.
Fruit trees, bushes and perennial vegetables: Mix one part loam (or sieved garden soil) with one part compost, and add some slow-release organic fertilizer.
Learn more about making seed starting soil and potting mix in this video.
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