If you have been reading about no-dig gardening, you have probably come across module sowing: raising seedlings one at a time in small individual cells, rather than scattering seed across an open tray and thinning out the losers later. It is a method popularised in the UK by market gardener Charles Dowding, among others, and it has a growing following here in Australia even though the exact trays he uses are a UK product and are not sold locally.
This guide is not affiliated with or endorsed by Charles Dowding. We are simply borrowing the logic of his module-sowing approach, a well-known and widely written-about gardening method, and mapping it onto the tube trays and pots that are actually available to Australian gardeners.
What module sowing actually means
Instead of sowing a whole tray of seed and pricking out the strongest seedlings later, module sowing gives every seed (or every couple of seeds) its own small cell of potting mix from day one.
Each seedling grows its own compact root ball, undisturbed by its neighbours. When it is time to plant out, you pop the whole root ball straight into the ground. There is no cutting apart of tangled roots, no setback while a disturbed seedling recovers, and far less transplant shock overall.
It suits gardeners who want to start seed indoors or under cover, get strong, even seedlings, and plant out only once each one is properly ready.
Why cell size and depth matter
Not every small pot is a good module. Two things decide whether a cell actually works for young seedlings:
Depth. A cell that is too shallow forces roots to circle back on themselves early, which stunts and stresses the plant. A cell with real depth lets the root grow straight down the way it wants to, right up until it is planted out.
Air pruning. This is the detail most trays get wrong. When a root reaches the bottom of a solid-walled pot, it has nowhere to go, so it curls around the base and keeps circling. This is called being "pot-bound", and a pot-bound seedling struggles to establish once it is in the ground. A tray with open or mesh cell bases lets air reach the root tip. The moment the tip meets air, it stops growing and the plant redirects that energy into producing more side roots instead. The result is a dense, fibrous root ball rather than one tightly wound root, and a seedling that establishes much faster after transplanting.
The UK trays vs what is available here
The seed trays associated with Dowding's method in the UK are a specific imported product, and they are not stocked by Australian nurseries or garden suppliers. If you have searched for them locally, that is likely why you have come up empty.
The equivalent locally is an air-pruning tube tray: a rigid tray of individual open-based cells, each holding its own tube pot, that gives you the same depth and root-pruning benefit in a product that ships within Australia.
Our 40-Cell Forestry Tube Tray
The 40-Cell Forestry Tube Tray with 50mm Native/Forestry Tube Stock Pots is the closest match to a Dowding-style module setup we stock. It is a 40-cell tray fitted with 50mm square tube pots, each one deep enough to give a root system real room to grow straight down, with open bases for air pruning.
It was built for raising Australian native seedlings and forestry stock in bulk, which happens to make it well suited to vegetable and flower module sowing too: forty individual, undisturbed root balls per tray, ready to plant out one at a time as each seedling reaches the right size.
If you already have trays and only need to replace or add tube pots, the 50mm Square Native/Forestry Tube Stock Pots are sold separately.
Sizing up before planting out
Some seedlings, particularly slower growers or anything you are starting well ahead of your planting-out date, outgrow a 50mm cell before conditions outside are ready for them. Rather than let roots sit cramped and circling, move them on into a larger pot for a few more weeks of growth.
The 63mm Square Squat Pots are a practical next size up. They give a growing root system more room without jumping straight to a full-size pot, and the square shape means they still pack tightly on a bench or trolley the way tube pots do.
A tray to sow into directly
Not every module needs its own separate pot. For fast growers, or for a first sowing you plan to thin and pot on shortly after germination, a solid propagation tray filled with seed-raising mix works as a simple, low-cost module bed.
The Propagation Trays - 35cm x 30cm come with an option with drainage holes and one without, so you can choose a version that suits how you water: holes for a tray you water from above, no holes for one you prefer to bottom-water or use as a catch tray under a cell insert.
Sowing, growing on, and transplanting
A simple module-sowing routine, using either the tube tray or the propagation trays:
- Fill each cell or tray with a good seed-raising mix, firmed gently, not compacted.
- Sow one or two seeds per cell, at the depth stated on the seed packet.
- Keep the mix evenly moist while germinating, never waterlogged.
- Once seedlings have their first true leaves, thin to the strongest single seedling per cell if you sowed more than one.
- Watch the root base. Once you can see a healthy web of white roots at the drainage holes or open base, the seedling is ready to plant out, or to pot on into a 63mm pot if outdoor conditions are not ready yet.
- When planting out, ease the whole root ball free rather than pulling on the stem. A well-grown module should slide out in one piece, roots and mix intact.
Because the root ball goes into the ground undisturbed, plants raised this way tend to sit still for a shorter period after transplanting and get on with growing sooner.
