Estimating seed yield before harvest with a simple scale

When you head out to collect acorns, walnuts or other hardwood seeds for a riparian restoration project, knowing roughly how much you will bring home lets you plan a cooler, plan transport, and avoid stripping a tree. Volunteers working with Potomac watershed focus often need a fast way to gauge the harvest of dozens of trees in a single afternoon. A small digital kitchen scale and a notebook are enough to turn guesswork into a defensible estimate, whether you are working along the Anacostia or coordinating a community day at a Melbourne creek-line site.

The same approach translates easily to Australian conditions, where bushcare groups and Landcare networks gather eucalyptus, acacia and banksia seed for provenance-based revegetation. A simple scale helps volunteers avoid the twin pitfalls of under-collecting, which leaves a site with too little for the nursery, and over-collecting, which can stress the parent tree. Below is a practical method you can run in the field without lab equipment, plus a few tips tuned to Australian seasons and rules.

Why a quick yield estimate helps your collection day

Most native seed is collected in short windows. In eastern Australia the wattle and eucalyptus seeds ripen between late spring and early autumn, and a heavy downpour can knock viable material to the ground overnight. If you wait until the end of the day to weigh everything, you may discover too late that one tree produced far less than expected and another was a quiet giant. Estimating seed yield before harvest lets you move on from light producers and spend longer under the champion trees.

For Growing Native, accurate forecasts matter because every kilogram of acorns or walnuts is promised to a state nursery that is counting on a certain seedling output. A volunteer who walks in with 18 kg instead of an expected 12 kg does not harm the project, but a surprise shortfall can leave a planting short of stock. Quick estimates also help with biosecurity. In NSW and Victoria, permit-holders collecting from public land often work under the frameworks set out in the Native Vegetation Act and the Environment Protection and Biodiversity Conservation Act 1999, and they may be asked to report expected collection volumes when the species is listed as a matter of national environmental significance.

Picking and using a simple scale in the field

A digital kitchen scale with a 0.1 g resolution and a 5 kg capacity is enough for almost any seed lot you will weigh. Models sold at Australian discount chains and hardware stores for around twenty to forty Australian dollars are accurate enough after a quick check. Place the scale on a flat rock or a clipboard, press the tare button with an empty container on top, and you are ready.

Before you trust the reading, verify it. A standard 5 cent Australian coin weighs roughly 2.8 g, and a 10 cent piece is about 5.65 g. If the scale reads those weights within a couple of decimal points, you are good to go. Keep a small windbreak nearby, because even a light breeze can blow lightweight eucalyptus samaras off the platform and throw off your total. A folded cardboard box works well as a shield in open paddocks around the slopes of Mount Lofty or the basalt plains near Melbourne.

Sampling a tree so the estimate holds up

The secret to a reliable estimate is a representative sample. Pick five to ten branches spread around the canopy at different heights and aspects, shake each gently over a tarp, and combine the fallen material in a single bucket. From that mixed bucket, scoop out a smaller working sample. A working sample of about 100 seeds, or roughly 30 to 50 g, is large enough to average out the natural variation between plump and shrivelled seed.

Repeat the sampling for each tree you plan to harvest. Do not assume two trees of the same species in the same gully will yield the same weight per seed, because soil depth, aspect and previous season's rainfall all shift seed size. In Brisbane's catchment reserves, for instance, the same Corymbia citriodora can produce noticeably smaller seed on a sandstone ridge than on a deeper alluvial flat. Treating each tree as its own batch keeps your final total honest, and the practice also gives you a free check on whether a tree has been hit hard by psyllids or lerp in the past summer.

Turning weight into seed count and total yield

Once you have weighed your working sample and counted the seeds inside it, you can calculate an average seed weight and scale up. The table below shows typical weights for some of the species Growing Native handles, plus a couple of common Australian natives for comparison. Use these figures as a sanity check rather than gospel, because local provenance will always shift the numbers a little.

Species (common name)	Average weight per 100 seeds	Seeds per gram	Notes for harvesters
Quercus rubra (northern red oak)	320 g	0.3	Large acorn, easy to count individually
Quercus alba (white oak)	380 g	0.26	Caps add weight, tare them off when possible
Juglans nigra (black walnut)	1,100 g	0.09	Husks removed before weighing
Carya ovata (shagbark hickory)	600 g	0.17	Husks can be left on for field estimate
Eucalyptus melliodora (yellow box)	0.15 g	670	Very fine seed, weigh in grams only
Acacia dealbata (silver wattle)	0.45 g	220	Hard-coated, store dry

To estimate the total yield of one tree, weigh your full harvest at the end of the session, then divide by the per-seed weight of that species. For example, if you collect 4.5 kg of yellow box capsules and you know 100 cleaned seeds weigh 0.15 g, you have roughly 4,500 divided by 0.0015, or around three million seeds, which is more than enough for most direct-seeding projects. The same logic in reverse lets you estimate kilograms from a known seed target: if a nursery has asked for 200 g of cleaned acorns and your sample shows 100 acorns weigh 320 g, you need about 62 acorns per kilogram-equivalent. Running the math at lunchtime, while the team refills water bottles and enjoys a quick arvo break, keeps the numbers fresh.

Refining estimates with moisture, debris and local rules

A raw field weight almost always overstates the clean, dry seed you will eventually hand over. Green husks, leaf litter, twig fragments and moisture can easily add 15 to 30 percent to the figure. To stay on the right side of the nursery's expectations, build a small adjustment into your estimate before you commit to a final number. The points below summarise the refinements most worth keeping in your kit.

Subtract a fixed debris percentage based on what you saw in the sample. If your 50 g sample contained 8 g of leaf and twig, treat your total as 84 percent clean seed.
Air-dry a small sub-sample in the sun for an hour, weigh it again, and use the difference to estimate the moisture loss between field weight and storage weight.
Record the tree's location, GPS point and aspect so future collections at the same site can compare year-on-year results.
Note any insect damage visible in the sample, and discount heavily chewed seed by eye before scaling up.
Photograph the working sample on a ruler or coin for a quick visual record that helps double-check later.
Check whether your collection area sits within a state forest, a council reserve or a private property, and confirm you have any required permits under the relevant state biodiversity legislation before you start.
Log your final estimate in a shared spreadsheet so volunteers at Growing Native's collection locations across the region can compare notes across seasons.

When you finish a session, weigh the harvest, divide by your species-specific seed weight and apply the moisture and debris factor. That final number is your working estimate of seed yield before the cleaning and drying stage begins. Over a few seasons the spreadsheet will start to show which trees in your patch are reliable producers and which are worth a pass in lean years. Pair that knowledge with the ecological context of the catchment you are restoring, and your group will turn a simple scale into one of the most useful tools in the field kit.