A grow-out trial plants a seed lot to renew it or to judge it, and a fair comparison of varieties grows them side by side under the same care and records emergence, flowering, ripening, yield and disease on the same dates. Repeat the trial for at least two seasons before ranking varieties, because one year’s weather can favour the wrong one.
Part of Community Seed Bank Management
A grow-out trial is a planting made to regenerate a seed lot or to compare varieties under the same conditions.
Two Reasons To Grow Out
Renewal. A lot whose germination has fallen to the action level is grown to produce fresh seed before the variety is lost. The Phase 2 viability guide advises renewing an important variety that tests below 70%. A renewal plot must follow all the seed-saving rules: enough plants, isolation, selection of survivors (Minimum Population Sizes).
Evaluation. New seed from a neighbour or a salvaged packet is unknown. A trial shows whether it suits your soil, season and diseases before you put it in the main fields.
Method For Fair Comparison
Step 1: Give each variety the same treatment. Same soil, same date, same spacing, same watering. If the plot slopes or one end is wetter, put every variety in each part, not one variety in the good corner.
Step 2: Repeat it within the plot. Plant each variety in two or more separate rows or beds, scattered. If a variety does well in one place and badly in another, the average is more honest than either.
Step 3: Include a check. Plant a variety you know in the same trial. Its result tells you what a normal season looked like.
Step 4: Record on a sheet, on set dates. Per variety: date sown, date of first emergence and percentage emerged, date of first flower, date of first harvest, yield per row (weigh it), disease and pest scores, taste and storage notes. For disease use a simple score such as 0 for none, 1 for slight, 2 for moderate and 3 for severe, assessed the same day for every variety.
Step 5: Compare in a table. Place the varieties in rows and traits in columns.
Step 6: Repeat for a second season. The ranking in a drought year differs from that in a wet one. A variety that is never the worst is often better than one that is sometimes the best.
Step 7: Decide and record. Keep, drop or trial again, and write the decision in the catalogue (Seed Inventory and Catalog System).
Worked Example: Reading Two Rows
Two bean varieties are each sown in two rows of 10 m. The weighed yields are variety A: 6.0 kg and 4.0 kg; variety B: 5.2 kg and 5.0 kg. Variety A averages (6.0 + 4.0) ÷ 2 = 5.0 kg per row and variety B averages (5.2 + 5.0) ÷ 2 = 5.1 kg. The averages are about equal, but A’s rows differ by 2.0 kg and B’s by 0.2 kg. A’s good row might sit on better soil, so on this evidence B is the steadier variety and a second season should decide. (The figures are invented to show the reading.)
Renewal Without Losing Diversity
- Grow more plants than the minimum, and take equal seed from each.
- Keep the old lot until the new seed has passed a germination test.
- Where possible, make the grow-out in a different place from the original, as a hedge against a local loss.
Common Mistakes
- Judging by one plant. Look at the row.
- Giving the new variety the best bed. The result will not hold in ordinary ground.
- Dropping a variety after one bad year.
- Not writing it down. The trial that is not recorded is a trial that will be repeated.
What’s Next
- Learn next: Landrace Development — turning trial results into local adaptation
- Combine with: Germination Rate Testing Protocol — when to renew