Starting seeds indoors in a seed tray is a surprisingly simple process. In fact, they grow perfectly happily in an inert medium like seed starting mix that contains no available plant food. That’s because all the food they need to start life is stored in the seed itself, made available in the form of cotyledon - “false” or “seed” leaves present on the seedling at germination.

When to Start Fertilizing Seedlings

Cotyledons and sterile planting mediums can only take your seedlings so far. At around the time the first “true” leaves appear (not the cotyledon), it’s time to provide supplementary nutrition to the seedling. In our experience, this is necessary even if starting the seedlings in a potting mix that does contain fertilizer, although your experience may differ depending on the exact mix used.

While the effect of delaying the first feeding won’t be immediately obvious, it’s important for the long term health of the plant. So don’t forget!

What to Feed Seedlings

We recommend feeding seedlings with compost and worm castings. They’re renewable, cheap (or free), and highly effective. If you don’t have either type of homemade composts available, purchase a 1:2:1 mixture of organic fertilizer. It’s best to dilute by half, so try to find a water-soluble option.

How Often to Feed Seedlings

After the first feeding, repeat on a once weekly cadence until you transplant the seedlings. At that point, they will need a different feeding plan.