Four Hundred Volunteers, Four Thousand Trees: Keeping the Dose Honest

By 11:40 the second shift had settled into a rhythm, and by 14:00 the rhythm had become a competition. Two holes got a full cup, so the next crew used half a cup to catch up. The last 600 trees went in with whatever was left in the bottom of the bags, which was mostly fines. When we audited the block three months later, 12 percent of the holes had more than four times the intended dose, 7 percent had none at all, and the over-dosed holes had the worst survival on the site.

Community and corporate planting days are the hardest application environment in the industry: hundreds of untrained hands, a tight schedule, and a message from the stage that more is better. The technical fix is not a better briefing. It is physical portion control.

Why the errors go both ways

Volunteers are not careless. They are working without feedback. A 40 g dose of gel looks like a teaspoon, and in a 50-litre hole a teaspoon looks absurd, so the natural instinct is to add more. The supervisor’s instruction to use one scoop competes with the visual evidence of a nearly empty hole, and the visual evidence wins.

Then the bags run low. The last hundred holes on a pallet get a thin scatter, and the crew at the far end of the block never sees a fresh bag because nobody is running supplies. Both errors are predictable, and both disappear when the dose arrives pre-portioned.

Portion control that survives a crowd

• Pre-fill 40 g paper cups or small sachets at the depot, one per tree, counted into trays of 50. A volunteer takes a cup, empties it, and drops the cup in a bin bag.
• Colour-code by rate if the site has two doses, and do not put two colours in the same tray.
• Station a supply runner with a vehicle, and set a rule that no crew walks more than 30 m for a refill.
• Mark every tenth tree with a flag; the supervisor samples the hole at each flag against a depth and dose card.
• Stop the planting at 15:30 whether or not the block is finished, and finish it with the paid crew the next morning.

The last item is the one organisers resist. Fatigue errors cluster in the final 90 minutes, and the marginal trees planted in that window cost more to replace than the day of paid labour saved.

The over-dose problem is real

On a clay site with poor drainage, four times the dose produced a swollen gel mass that filled the planting hole and displaced the backfill. The roots sat in a saturated pocket with no air, and those trees were the first to fail in the wet month that followed. On a sandy site the same over-dose would have been wasteful but harmless. The risk depends on the soil, which is why the supervision card should say what the soil is, not just the number of grams.

Under-dosing is quieter. A hole with no gel simply behaves like a hole with no gel, and on an irrigated site it may survive the first season and fail in the second, by which time nobody connects it to planting day.

What to record on the day

Four numbers per block: trays issued, trees planted, cups returned, and the supervisor’s sample result at each tenth tree. Trays issued minus cups returned should be close to trees planted; a gap of more than 3 percent means cups went into pockets, bins or the wrong block. Photograph the sample holes at three flags per block, with a tape measure and the date board.

That record is also the only defence you have if a funder or council asks why survival was 78 percent on a site that was supposed to be a showcase. We have seen a well-run community day with full records survive that conversation, and a poorly run one without records lose the next year’s funding.

Before the next planting day, order the cups, print the tray count sheet, and brief the crew leaders on the 15:30 stop rule. If the site is clay, halve the dose and say so on the card. The mixing and dose guidance for our granular water retaining gel includes a per-hole table you can print at A5 for a volunteer briefing.