seed raising and potting mix recipes

Ingredients
Sand – I get mine from Thomas’ landscapers in Lawson because they sell most of their landscaping materials in smaller bags as well as by the tonne! I get a large bag of sand for $6 which lasts me for a while unless I am doing a lot of large pots (having said that I have also just seen a garden nursery sell bags of this stuff too). The type of sand you get is critical. The stuff that I use is called ‘washed river sand’ (aka concrete sand) – it is course (large grained) and pH neutral. DO NOT use ‘brickies sand’ or ‘fat sand’ used for making cement, as these are fine beach sands with a pH of around 10 (far too alkaline) !!!. The sand is present in the seedraising/potting mixes to provide airation. I am not sure where the ‘washed river sand’ comes from and what the environmental impact of the mining process is. If anyone knows of a non-mined alternative to sand, I would appreciate if you could let me know

Coir peat. This replaces traditional peat which is unsustainably mined in places like Canada, Ireland and Denmark. It is present in the seedraising/potting mix to hold water (I also prefer it to the composted wooodchips that are often added to commercial seedraising/potting mixes for the same reason). Also known as coco-peat it is a valuable by-product of the coconut industry and has only really been commercialised in the last 10 years or so. It is sold compressed into ‘bricks’ of various sizes and dimensions. You can get these in most garden centres or hardware stores, sometimes sold alongside ‘worm farm’ products, the smallest ones being around $3 or so. The idea is that you add the compressed ‘brick’ to water and it expands to give you up to 9litres of fine coco peat which you can then mix as desired. Beware of ‘value added’ products that helpfully contain slow release chemical fertilisers!!. You can also get a much rougher product with chunks of husk still present – useful for potting mixes for larger plants.

Compost. If your own compost is up to the job then all the better, otherwise I have found a BFA certified organic input made by Kreidmans. It is composted vegetable scraps and is sold by the 30litre bag. The produce store in north Katoomba stocks this product. The job of compost in the potting mix is to hold nutrient. The humus in the compost has the capacity to hold nutrients in store until they are needed by plants. (by ‘up to the job’ I mean the produce of a good hot composting process that kills plant pathogens – young seedlings are extremely vulnerable to fungal rot)

Nutrition. Used in larger quantities in potting mix and in smaller quantities in seedraising mix since the germinating seeds don’t need (and in fact can be damaged by) by too much nutrition. The compost will provide some nutrition, but I also like to add some more reliable source of NPK plus trace elements so as to err on the side of lush growth while the plant is in the pot (as opposed to the garden soil which is a different story). I have found the best source of this to be granular (not pelleted) products such as Dynamic Lifter or Organic Life which are based on composted chicken manure. Worm castings can be used for potting mixes, but not seed raising mixes because of the likely presence of pathogens which can cause ‘damping off’ or other fungal disease problems in seedlings.

Seed rasing mix
3 parts washed river sand, 3 parts coir-peat, 1 part compost. If the seedlings are likely to stay in the mix for a while, you can add half a part of nutrition, or make sure that you feed with liquid fertiliser (eg the product Charlie Carp which is made from boiled down carp which is a pest in the Murray river) regularly from 4 leaf stage.

Potting Mix
3 parts washed river sand, 3 parts coir peat, 2 parts compost, 1 part nutrition. For larger plants I would consider using the rough coco-peat as it allows more space for larger root development.