Overhead watering does three unhelpful things in a propagation house: it keeps the media surface wet, it knocks small seed about, and it splashes soil-borne pathogens onto leaves. Watering from below avoids all three, and it also waters more evenly than any hand can.
The two products here do the same job at different scales.
The comparison
| Measure | Capillary matting | Self-watering trays |
|---|---|---|
| Waters mixed pot sizes | Yes, anything sitting on it | No, fits its own cells |
| Bench area covered | A whole bench from one roll | One tray each |
| Cost to start | Higher | Low |
| Needs a level surface | Yes, critically | Less so |
| Algae growth | Real on a lit mat | Lower, water is enclosed |
| Cleaning between crops | Wash or replace the mat | Wash the tray |
| Works with pots with no drainage | No | Not applicable |
Matting only works if the bench is level
Capillary matting relies on water spreading through the fabric and being drawn up through the drainage holes of whatever sits on it. On a bench with any fall, water collects at the low end and the high end dries out, and the crop tells you exactly where the slope is. Level the bench before laying Kapmat Capillary Matting, 72 in x 5 yd ($148.78), and check the pots make firm contact, since a pot with a raised rim on its base never touches the mat at all.
The other thing matting needs is a reservoir arrangement, either a shallow tray under one end or a drip line keeping the mat damp. A mat that is merely wetted each morning dries by afternoon in a bright house and the whole advantage is lost.
Wicking trays are the low-effort version
A set of Hanaoyo Self-Watering Seed Starter Trays, 96 Cell, 2-Pack ($12.49) does the same thing for a standard cell tray with no levelling, no reservoir plumbing and no algae to scrub. You fill the lower chamber, the wick keeps the media damp, and the surface stays dry. For a home greenhouse raising a few hundred seedlings a year this is the answer, and the cost difference is substantial.
The limitation is that they suit their own cells. A bench of assorted 9 cm pots, recovered houseplants and a few grow bags is not a job for wicking trays.
Algae, and why it appears
A permanently damp mat under bright light grows algae, which is unsightly, slippery and a food source for fungus gnats. It is a light problem rather than a water problem: shading the mat where pots do not cover it, or covering it with a perforated liner, largely prevents it. Replacing the mat between seasons is cheap enough that it is not worth fighting a badly colonised one.
The decision, summarised
- Standard 1020 cell trays, home scale: wicking trays, and spend the difference on lights.
- A whole bench of assorted pot sizes: capillary matting, on a level bench.
- Away for a weekend in spring: either, and both beat asking a neighbour to water.
- Recurrent damping-off or fungus gnats: switch to bottom watering before buying any treatment.
- Bench that cannot be levelled: wicking trays, because matting will not water evenly.
