Kratky Seed Starting: Seeds to Seedlings for Your Kit

Good Kratky seed starting sets up the whole crop. A strong seedling with healthy roots settles into a Kratky kit quickly; a weak, stretched one struggles. Here is how to go from seed to transplant.

What you need

• Seeds of a crop suited to Kratky (see best plants for Kratky)
• Rockwool cubes, coco coir plugs or peat plugs
• A tray to hold them, ideally with a clear humidity dome
• Water, and a weak nutrient solution once seedlings have leaves
• Light: a bright window or a grow light

The comparison of rockwool and clay pebbles explains the options for media.

Step 1: Prepare the cubes or plugs

Moisten the plugs. Rockwool is usually soaked first in water adjusted toward the pH you will grow at, as its packaging directs. Squeeze out excess water so the cubes are moist rather than waterlogged.

Step 2: Sow

Place two or three seeds in the hole of each cube or plug. Small seeds such as lettuce need light to germinate and should only be pressed in lightly. Larger seeds can sit a little deeper. Follow the seed packet's sowing depth as a guide.

Step 3: Keep warm and moist

Cover the tray with a humidity dome or plastic to hold in moisture, and keep it somewhere comfortably warm. Check daily so the plugs do not dry out. Germination times vary widely by crop: lettuce and basil are usually quick, while parsley is known for being slow.

Step 4: Give light as soon as they sprout

Once seedlings appear, remove the cover and give them strong light straight away. Seedlings in dim light stretch into long, weak stems within days. A grow light a short distance above the tray, set as the manufacturer advises, prevents this. See Kratky grow lights.

Step 5: Thin and feed

When the seedlings have their first true leaves, keep the strongest in each plug and snip the others at the base. Cutting rather than pulling avoids disturbing the roots of the one you keep. At this stage, water the plugs with a weak nutrient solution, typically well below full strength, so they have something to grow on. See Kratky nutrients.

Step 6: Transplant into the kit

Seedlings are ready to move when they have a couple of true leaves and roots are poking out of the bottom or sides of the plug. Place each plug in a net pot, fill around it with clay pebbles if your kit uses them, and seat it in the lid with the solution just touching the bottom of the pot. Full steps are in Kratky kit setup.

Common seed-starting mistakes

• Too little light after sprouting: causes leggy seedlings.
• Waterlogged plugs: can rot seeds before they sprout.
• Letting plugs dry out: can kill germinating seeds.
• Leaving the dome on too long: encourages damping off, a fungal problem that makes seedlings collapse at the base.
• Transplanting too early: roots that cannot reach the solution leave the seedling stranded.

Sowing directly in the kit

Some growers sow straight into a plug sitting in the net pot of the kit. This works, but the whole reservoir is tied up during germination and light must be kept off the solution. Starting in a separate tray lets you choose only the strongest seedlings to transplant.

Cuttings as an alternative

Basil and mint root easily from cuttings stood in water. See the Kratky herb kit article for details.

Frequently asked questions