If you're scaling cut flower production, one of the most critical decisions you'll make happens before a single seed hits the tray: how many seeds per flat? Get it wrong and you're either wasting expensive pelleted seed or crowding plugs into a root-bound mess that never recovers at transplant.
This guide covers exact plug tray seeding rates for the five most commercially important cut flower crops — lisianthus, snapdragon, dianthus, gerbera, and lobelia — so you can order the right quantity, fill your trays with confidence, and hit your transplant windows on schedule.
For smaller-pack options and retail seed quantities, visit our sister site at TrailingPetunia.com Collections.
Why Seeding Rate Matters More Than You Think
Commercial plug production is a numbers game. Every cell in a 288-flat costs money — in heat, humidity, labor, and bench space. Seeding too thin means empty cells and wasted infrastructure. Seeding too dense means thinning labor, disease pressure, and stunted root systems.
The crops covered here each have distinct germination profiles, seed sizes, and plug development timelines. A one-size-fits-all approach will cost you. Use the crop-by-crop rates below as your baseline, then adjust for your germination room conditions and seed lot quality.
Understanding Plug Tray Cell Counts
| Tray Format | Cells Per Flat | Cell Volume | Best For |
|---|---|---|---|
| 512-cell | 512 | Very small | Lobelia, fine seed crops |
| 288-cell | 288 | Small | Lisianthus, snapdragon, dianthus |
| 128-cell | 128 | Medium | Gerbera, larger plugs |
| 72-cell | 72 | Large | Gerbera finish plugs, large transplants |
Lisianthus: Seeding Rates & Plug Tray Protocol
Lisianthus is the most technically demanding crop in this guide — and the most rewarding. Pelleted seed is standard for commercial production, with one pellet per cell in a 288-cell tray. Do not double-seed lisianthus. Crowding at the plug stage is a primary driver of rosette disorder, which can wipe out an entire crop.
| Tray Format | Seeds Per Flat | Seeds Per Cell | Notes |
|---|---|---|---|
| 288-cell | 288 | 1 pelleted | Standard commercial rate |
| 128-cell | 128 | 1 pelleted | For larger plug finish |
Germination: 75–80°F, high humidity dome, light required — do not cover seed. 10–14 days to germination. Plug finish: 10–12 weeks.
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Snapdragon: Seeding Rates & Plug Tray Protocol
Snapdragons are a high-volume cut flower crop with fast plug development. Pelleted seed is strongly recommended for accurate cell placement.
| Tray Format | Seeds Per Flat | Seeds Per Cell | Notes |
|---|---|---|---|
| 288-cell | 288–576 | 1–2 | 1/cell pelleted; 2/cell raw with thinning |
| 512-cell | 512–1,024 | 1–2 | High-density starts, thin to 1 at cotyledon |
Germination: 65–70°F, light required, do not cover. 7–10 days. Plug finish: 4–6 weeks.
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Dianthus: Seeding Rates & Plug Tray Protocol
Dianthus is a reliable, fast-germinating crop. Pelleted seed allows precision seeding; raw seed works with 2-per-cell and thinning.
| Tray Format | Seeds Per Flat | Seeds Per Cell | Notes |
|---|---|---|---|
| 288-cell | 288–576 | 1–2 | Pelleted: 1/cell; raw: 2/cell, thin at cotyledon |
| 128-cell | 128–256 | 1–2 | Larger plug for direct field transplant |
Germination: 65–72°F, light helpful. 5–8 days. Plug finish: 4–5 weeks.
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Gerbera: Seeding Rates & Plug Tray Protocol
Gerbera requires more space per plug. A 128-cell tray is the commercial standard — gerbera plugs develop a substantial root system and need cell volume to avoid stunting.
| Tray Format | Seeds Per Flat | Seeds Per Cell | Notes |
|---|---|---|---|
| 128-cell | 128 | 1 | Standard; sow seed upright, tip down |
| 72-cell | 72 | 1 | Large finish plugs or direct pot production |
Germination: 70–75°F, tip down at 45°, barely covered. 7–14 days. Plug finish: 6–8 weeks.
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Lobelia: Seeding Rates & Plug Tray Protocol
Lobelia seed is extremely fine. Multi-pelleted seed is the standard for commercial production. Do not cover — lobelia requires light to germinate.
| Tray Format | Seeds Per Flat | Seeds Per Cell | Notes |
|---|---|---|---|
| 512-cell | 512 | 1 multi-pellet | Standard; do not cover |
| 288-cell | 288 | 1 multi-pellet | Larger plug for earlier transplant |
Germination: 70–75°F, light required, do not cover. 10–14 days. Plug finish: 6–8 weeks.
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Quick-Reference: Seeds Per Flat by Crop
| Crop | Tray | Seeds/Flat | Seeds/Cell | Germ Temp | Plug Finish |
|---|---|---|---|---|---|
| Lisianthus | 288-cell | 288 | 1 pelleted | 75–80°F | 10–12 wks |
| Snapdragon | 288-cell | 288–576 | 1–2 | 65–70°F | 4–6 wks |
| Dianthus | 288-cell | 288–576 | 1–2 | 65–72°F | 4–5 wks |
| Gerbera | 128-cell | 128 | 1 | 70–75°F | 6–8 wks |
| Lobelia | 512-cell | 512 | 1 multi-pellet | 70–75°F | 6–8 wks |
Shop Our Cut Flower Seeds
Related Posts
- Lisianthus Seed Starting Guide – Germination, Plug Trays & Rosette Prevention
- Cut Flower Seed Starting Guide for Strong Stems
- Flower Seed Germination Times – Complete Chart by Variety
- How to Grow Snapdragons from Seed for Cut Flower Production
- Cut Flower Seed Starting Calendar – Indoor Start, Transplant & Direct Sow Dates by USDA Zone
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FAQ: Seeds Per Flat for Cut Flower Crops
How many seeds go in a 288-cell flat?
For most cut flower crops — including lisianthus, snapdragon, and dianthus — you sow one pelleted seed per cell, for a total of 288 seeds per flat. With raw seed, sow 2 per cell and thin to 1 at the cotyledon stage.
What tray size is best for lisianthus plugs?
A 288-cell tray is the commercial standard. One pelleted seed per cell is critical — do not double-seed. Overcrowding is a leading cause of rosette disorder.
How many seeds per flat for snapdragons?
288 seeds per flat (1 pelleted/cell in a 288-cell tray). With raw seed, sow 2/cell and thin at cotyledon. Plug finish: 4–6 weeks at 65–70°F.
What is the seeding rate for gerbera in plug trays?
128-cell tray at 1 seed per cell (128 seeds/flat). Sow tip down at 45°, barely covered. Germination: 7–14 days at 70–75°F. Plug finish: 6–8 weeks.
How do I seed lobelia in plug trays?
1 multi-pellet per cell in a 512-cell tray (512 seeds/flat). Do not cover — light required. Maintain 70–75°F. Germination: 10–14 days.
How many flats do I need for a commercial planting?
Divide your target transplant count by cells per flat. Example: 5,000 lisianthus ÷ 288 = ~18 flats. Always add 10–15% overage for losses and culls.
Where can I buy commercial-quantity cut flower seeds?
Browse our full catalog at trailingpetuniabulkseeds.com or visit TrailingPetunia.com Collections for smaller pack sizes.