Hydroponic Plugs Drying Out: Humidity Domes Plus Wicking
Hydroponic plugs drying out usually lack a humidity dome, sit somewhere too warm or lose contact with the water below. University of Minnesota Extension notes that clear plastic domes let light in and help stop moisture from escaping. Cover the tray, water from below plus give plugs a steady path to water.
The short answer
Plugs dry out when moisture escapes faster than it is replaced. University of Minnesota Extension advises clear domes over trays plus notes that excess daytime heat can dry the mix and kill seedlings. Water from below so the whole plug wets, then drain extra water. In a wicking system, a wick carries solution to the root zone.
How do plugs take up water?
University of Minnesota Extension notes that it is easy to mist the top of the mix and let the rest of the container become dry. It suggests pouring water into the tray so it wicks up into the mix.
Drain any excess water that remains in the tray afterward, the same source advises, so roots stay in good condition.
UC Agriculture and Natural Resources describes a wicking system where a wick brings water plus nutrients from the reservoir to the root zone. Common wick materials are nylon, polyester plus cotton.
Why does a humidity dome help?
Clear plastic domes that fit over trays allow light in and help hold moisture in, University of Minnesota Extension explains. They slow drying in the top layer where seeds sit.
The same source advises removing domes when the seedlings are tall enough to touch them.
University of Minnesota Extension also notes that excess heat during the day can dry out the mix, leading to seedling death.
| Sign | Likely cause | Fix |
|---|---|---|
| Dry top with damp base | Misting only the surface | Water from below through the tray |
| Whole tray drying fast | No dome or excess heat | Cover with a clear dome plus move from heat |
| New pellets stay hard | Coir not fully expanded | Soak until expanded |
| Water pooling in the tray | Excess water left behind | Drain the tray |
Source: University of Minnesota Extension plus UF/IFAS Extension.
Does the plug material matter?
UF/IFAS Extension notes that rock wool comes in cubes with prefabricated holes for seed placement. Most rock wool products need soaking in a pH buffer solution to remove natural alkalinity.
Coconut fiber pressed into pellets or bricks also needs a soak to expand before use.
UF/IFAS Plant Propagation describes a plug as a seedling grown in a small volume of medium in a small cell.
How to: step by step
- Soak rock wool cubes in a pH buffer solution or soak coir pellets until expanded.
- Place plugs in a tray plus water from below.
- Pour off extra water left in the tray.
- Cover the tray with a clear plastic dome.
- Shift trays away from excess daytime heat.
- Remove the dome once seedlings touch it.
Troubleshooting
Dry crusty tops: no dome. Cover the tray.
Dry plugs over water: poor contact. Water from below or add a wick.
Soggy dark plugs: too wet. Drain extra water.
For related reading see damping off cannabis seedlings, seedling heat mats for cannabis plus caring for your hydroponic system. Kind Seed Co also stocks cannabis seeds.
Sources
- Seed germination: plug production, UF/IFAS Plant Propagation
- Growing lettuce in small hydroponic systems (HS1422), UF IFAS Extension
- Starting seeds indoors, UMN Extension
- Wicking hydroponics: a soilless growing method, UC Agriculture plus Natural Resources, Master Gardeners
FAQ
Should plugs be soaked first?
Yes for many types. UF/IFAS Extension notes that most rock wool products need soaking in a pH buffer solution to remove natural alkalinity. Coconut fiber pellets plus bricks need a soaking period to expand before use. Starting with fully wet plugs makes even moisture far easier.
When should the dome come off?
University of Minnesota Extension advises removing domes when the seedlings are tall enough to touch them. Until then, a clear dome allows light in and helps hold moisture in the tray. Once it is off, check plugs more often because they will dry faster.
How does a wicking system work?
UC Agriculture plus Natural Resources describes a wicking setup with a watertight reservoir, a wick plus grow media. The wick brings water plus nutrients from the reservoir to the root zone. An overflow tube limits reservoir height so the grow media does not fill with excess solution.
Can heat dry out plugs?
Yes. University of Minnesota Extension notes that excess heat during the day can dry out the mix, leading to seedling death. Check plug moisture daily when trays sit somewhere warm.
Why water from below?
University of Minnesota Extension notes that misting can wet the top while the rest of the container stays dry. Adding water to the tray lets it move up into the mix. Drain any water left in the tray afterward so roots are not left standing in excess water.
