Starting seeds and cuttings in the tropics requires more than just good weather—it’s all about creating the right growing environment. In this guide, Carol Laing shares practical tips for crafting effective potting and seed-raising mixes using organic materials suited to tropical conditions, ensuring strong, healthy roots from the very start.
What plants need to grow:
Sunlight, Water, Air, Drainage, Nutrients, and Root support
Seed raising mixes also need to have a pH between 5.5 and 6, the nutrients calcium and magnesium to meet the high demand at germination.
After making your mix, water until it starts to drain, after it has stopped draining, pick up a handful and give it a squeeze, if a few drops form between your fingers, that is perfect, at about 40-50% moisture. Anymore and it is too wet.
If this happens you will need to add more drainage materials, either sand, perlite/vermiculite.
Materials and their properties for making potting mixes
Coconut coir: Hold moisture, has good aeration and hold
Coarse Sand: Reasonable aeration, good for drainage mixed with other ingredients. Sifted sand for raising seedlings, coarse sand for propagation of cuttings and potting mix.
Compost aged: Holds moisture, reasonable aeration, plant food, microbes.
Good to germinate seeds then prick out and pot on.
Perlite: Light weight sterile material holds moisture, good drainage, good aeration, and it lightens the weight of the mix.
Made from a natural rock. No nutrients.
Vermiculite: Light weight sterile product, holds moisture very well, good aeration, good drainage, holds roots, does not rot down.
Good light weight covering for seeds.
Worm castings: Holds moisture, nutrients, microbes, antibiotics and has
Antifungal properties.
Organic Potting Mixes
Searles Organic Potting Mix (sieved) plus 20% worm castings or 20% compost, will make a mix suitable for seedlings, propagation of cuttings and for potting on. Only Premium potting mixes have fertiliser added.
Homemade Seed raising mixes
1 part moist coir, 1 part Vermiculite or Perlite, 1 part compost — plus 20% worm castings
Coarse sand may be used instead of Vermiculite and Perlite.
Biochar with added worm castings, or liquid organic fertilisers will hold nutrients, have spaces for bacteria and will last for years.
Rockdust will supply a range of minerals.