Start Seeds for Kratky
Lesson 5 of 14
Most Kratky plants start life in a small cube or plug of growing medium. Once roots grow out of the bottom, the seedling moves into its container.
Choose a starting medium
- Rockwool cubes are the most common. Soak them in pH-adjusted water before sowing, because new rockwool can be alkaline.
- Coco coir or peat plugs work the same way and are easier to find in garden centers.
- You can also sow straight into a net cup filled with clay pebbles or another medium, set over the solution. It works, but tiny seeds can wash down between pebbles.
Sowing
- Place two or three seeds in the hole on top of each moistened cube or plug.
- Lettuce seed needs light to germinate, so cover it only very lightly or not at all.
- Keep the cubes in a tray with a little water in the bottom so they never dry out.
- A clear cover or plastic bag keeps humidity up until the seeds sprout. Remove it once they do.
After they sprout
- Give seedlings strong light straight away. Seedlings in dim light stretch into long, weak stems.
- When the first true leaves appear, keep the strongest seedling in each cube and snip off the others at the base.
- Keep the cubes moist, not sitting in deep water.
When to transplant
A seedling is ready when roots begin to poke out of the bottom of the cube and it has its first true leaves. For lettuce this usually takes one to three weeks, depending on warmth and light. You will move it into its container in Lesson 8.
Your task for this lesson
Sow a few more cubes than you need. Extra seedlings give you a choice of the strongest plant and a spare if one fails.