Watering is where most microgreens problems start. Too little and the seedlings wilt and fall over; too much and mold appears within a day or two. The good news is that the right method is simple: mist the surface while seeds germinate, then switch to bottom watering once the seedlings are uncovered.
Quick guide
- At sowing: moisten the medium so it feels like a wrung-out sponge.
- During blackout: mist the surface once or twice a day only if it looks dry.
- After blackout: bottom water about once a day — roughly 1–2 cups (250–500 ml) for a 10×20 tray.
- Before harvest: skip watering for 12–24 hours so the leaves are dry.
Stage 1: Moisten the medium before sowing
Water the soil, coco coir or mat before the seeds go on. For loose media, mix water in until a handful holds together when squeezed but only releases a drop or two of water. The medium should be evenly damp all the way through.
Starting with the right moisture means you rarely need to water heavily during germination, which is when seeds are most vulnerable to rot.
Stage 2: Mist during germination and blackout
Seeds need constant surface moisture to germinate, but not puddles. During the blackout period:
- Lift the cover once a day.
- If the seeds or surface look dry or pale, mist until they glisten.
- If the surface already looks wet, skip it.
Use a fine spray bottle so you do not wash seeds into clumps.
Stage 3: Bottom water after blackout
Once seedlings are uncovered and standing up, stop watering from above. Water sitting on dense foliage is a major cause of mold and damping off. Bottom watering keeps the leaves dry and encourages roots to grow down.
You need two trays
- A growing tray with drainage holes, holding the medium and microgreens.
- A solid tray without holes that the growing tray sits in.
How to bottom water
- Lift the growing tray out.
- Pour water into the solid tray: about 1–2 cups (250–500 ml) for a 10×20 tray, or around ½ inch (1 cm) of depth.
- Set the growing tray back in and let it soak for 10–15 minutes.
- Lift it out again and pour away any water left in the bottom tray. Roots sitting in standing water can rot.
For small containers without a separate tray, set them in a shallow dish of water for a few minutes, then drain.
How often to water microgreens
Most trays need bottom watering once a day. Large crops such as peas and sunflower may need water twice a day in the final few days, because they hold a lot of foliage. In a cool, humid room, every other day may be enough.
The best way to judge is weight. Lift the tray right after watering to learn how a full tray feels, then lift it again the next day. A noticeably lighter tray needs water.
| Stage | How | How often |
|---|---|---|
| Sowing | Pre-moisten medium | Once |
| Blackout (days 1–4) | Mist surface | Only when dry, usually once a day |
| Light (day 4 to harvest) | Bottom water | Usually once a day |
| Last day | Stop watering | 12–24 hours before cutting |
Signs of under-watering
- Seedlings droop or lie flat, especially late in the day.
- Leaves look dull or feel soft.
- The tray feels light, and the medium pulls away from the sides.
Under-watered microgreens usually recover within an hour or two of bottom watering. If they still lie flat after that, the cause may be something else — see why microgreens fall over.
Signs of over-watering
- Grey, cobweb-like fuzz spreading over the surface or stems (mold).
- A sour or musty smell.
- Stems that turn brown, pinched or slimy at the base (damping off).
- Water still sitting in the bottom tray hours after watering.
If you see these, water less, add gentle airflow with a small fan, and reduce seed density next time. Not every white fuzz is mold, though — learn to spot root hairs vs mold.
Water quality and temperature
Ordinary tap water is fine for microgreens. Use it at room temperature: very cold water can slow growth. If your tap water is heavily chlorinated and you notice it smells strongly, let it stand in an open jug overnight before using it. Fertilizer is not needed for most crops, which grow on the seed’s own stored energy.
Watering microgreens on hydroponic mats
Mats made of hemp, jute or coco fibre hold less water than soil and dry out faster. Keep a thin layer of water in the bottom tray (just touching the mat) during the light stage, and refresh it daily so it does not go stale. More on this in growing microgreens without soil.
Frequently asked questions
Can I water microgreens from the top?
During germination, a fine mist from above is fine. After that, top watering wets the leaves and increases the risk of mold, so bottom watering is better.
Should the water drain completely?
Yes. Let the tray soak for 10–15 minutes, then pour off the excess. Microgreen roots need both water and air.
My medium dries out on top but is wet underneath — what should I do?
That is normal with bottom watering. The surface can look dry while the root zone is moist. Judge by tray weight and how the seedlings look, not by the surface.
