How and Why to Thin Your Seedlings

Using tweezers to thin very tiny Night Phlox seedlings

I often sow too thickly, I think patience, or the lack of, has something to do with it! We place tiny seeds in a glassine, tapping it gently to move the seeds to the envelope’s edge and then into the seed trays below. Even so, often we get too many seedlings emerging.

Thinning, or removing weak or later germinating seedlings gives new seedlings more room and ample access to water and sunlight. The best, most robust seedlings are left to develop without competition. These will later become your best plants. We thin early, as later the seedling roots entwine and make removal difficult. Tweezers are a good tool to use if the seedlings are small.

If you have sown your seeds outdoors, thinning is done in stages, just in case slugs or other pests take out some seedlings. Second, or even third thinnings, spaced a week apart, may be needed until you reach the final spacing requirements for each variety.

Thin by gently pulling or pinching off at soil level as soon as seeds germinate. Thin at least twice, first spacing to 3” apart and discarding the extras, the second thinning 2-3 weeks later to final spacing as indicated on the packet. Transplant these extras from the second thinning, if desired.