May, Jun, Jul, Aug
After you've sown your seeds and they've germinated, they may be crowded, uneven and competing for resources. When large enough to handle, you will need to thin them.
Carefully pull out the seedlings with as little disturbance to the others as possible. Pull up the weaker ones at regular spacings. This is best done when the soil is damp.
Check the seedlings that are left, firming them in if they've been disturbed and have become loose. If there are any large gaps, replant spare seedlings into them.
Thinning your plants gives them space to grow to larger leaves and dense hearts.
Water the remaining seedlings gently, using a light spray from a hose or watering can with a rose, so you don't wash away soil from the row and dislodge any seedlings.