Grow Light for Dahlias Indoors: Pre Sprouting Tubers
A grow light for dahlias indoors helps tubers potted early in spring grow sturdy shoots before they go into the garden. Pre sprouting starts with sound tubers from winter storage. University of Minnesota Extension notes light distance changes light intensity. A close light plus a timer gives compact shoots.
The short answer
Start with firm tubers that stored well over winter. Pot them up, then grow the shoots under a light. University of Minnesota Extension suggests 6 to 12 inches for flowering houseplants with 14 to 16 hours of light a day. Plant out after frost, covering tubers 3 inches deep.
How should tubers look before potting?
University of New Hampshire Extension notes any damage to tubers lets disease organisms in, leading to rot. It advises removing tubers that have started to rot before decay spreads. It notes storage that is too wet makes tubers likely to rot. Pot only firm tubers with no soft spots.
| Step | Guide | Source |
|---|---|---|
| Winter storage | 35 to 45 F in vermiculite or dry sand | North Carolina State Extension |
| Winter storage | 40 to 50 F, dry location | Iowa State University |
| Light height | 6 to 12 inches (flowering plants) | University of Minnesota |
| Hours per day | 14 to 16 (flowering plants) | University of Minnesota |
| Planting depth | 3 inches | North Carolina State Extension |
Source: North Carolina State Extension, Iowa State University Extension plus University of Minnesota Extension.
How much light do dahlia shoots need?
University of Minnesota Extension notes the distance between a light and a plant changes the light intensity. It suggests 6 to 12 inches for flowering houseplants plus 4 to 6 inches for seedlings. It suggests 14 to 16 hours a day for flowering houseplants. A timer holds the schedule steady.
When do dahlias go outside?
North Carolina State Extension notes tuberous roots can be injured below 25 F, so dahlias are often grown as annuals. Wait until frost has passed before planting out. North Carolina State Extension advises covering tubers to a depth of 3 inches. Ease potted shoots into outdoor light before planting.
How to: step by step
- Inspect stored tubers plus discard any with rot.
- Pot sound tubers in a soilless mix.
- Hang the light 6 to 12 inches over the pots.
- Set a timer for 14 to 16 hours.
- Lift the light as shoots grow.
- Plant out after frost, 3 inches deep.
Troubleshooting
Soft or rotting tubers: storage too wet or damaged skin. Discard them before decay spreads.
Pale, stretched shoots: light too far away. Lower it toward 6 inches.
Shoots touching the light: growth caught up. Raise the light to restore the gap.
For related reading see grow lights for cannabis, LED light distance for cannabis plus grow light timers. Kind Seed Co also stocks cannabis seeds.
Sources
- Dahlia, North Carolina State Extension
- How do I over winter dahlias, Iowa State University Extension
- When should I dig dahlia tubers and how should I store them, University of New Hampshire Extension
- Lighting for indoor plants and starting seeds, University of Minnesota Extension
FAQ
How far should a grow light be from dahlia shoots?
University of Minnesota Extension suggests 6 to 12 inches for flowering houseplants plus 4 to 6 inches for seedlings. It notes the distance between a light and a plant changes the light intensity. Start near the closer end for young shoots, then raise the light as the stems grow taller.
How many hours of light do potted dahlias need?
University of Minnesota Extension suggests 14 to 16 hours a day for flowering houseplants. A timer holds that schedule steady, so the shoots get the same light each day. Plants still get a dark period every night, and the timer removes the need to remember the switch.
How should dahlia tubers be stored over winter?
North Carolina State Extension advises storing tubers in vermiculite or dry sand at 35 to 45 F. Iowa State University Extension suggests a cool, dry spot at 40 to 50 F. University of New Hampshire Extension notes a storage medium that is too wet will likely make the tubers rot.
Which tubers should not be potted?
University of New Hampshire Extension notes damaged tubers let disease organisms enter, which leads to rot. It advises removing any tubers that have started to rot before the decay spreads. Pot only firm tubers with sound skin, and set aside any tuber that feels soft.
How deep should dahlia tubers be planted outside?
North Carolina State Extension advises covering tubers to a depth of 3 inches when planting. It notes tuberous roots can be injured at temperatures below 25 F, which is why dahlias are often grown as annuals in cold areas. Wait until frost has passed before moving potted dahlias out.
