When you start a vegetable garden by direct seeding, thinning out the plants is a necessary chore.
As the plants sprout, they are generally overcrowded. Failure to properly thin them will result in a dismal harvest of small and substandard crops, especially with root crops , potatoes, beets, onions . Thinning seedlings produces higher yields by Allowing space for proper growth, Reducing competition for moisture and nutrients, and by allowing for proper air circulation between plants.
When thinning out your recently germinated seedlings, save the strongest seedlings and remove the runts, poorly formed and late blooming plants. You may find it necessary to pinch out or cut the excess seedlings of some vegetables if they are too overcrowded to avoid damaging the root system of neighboring plants.
Some plants if carefully removed , can later be transplanted to other available spaces, and you may also need some later if the remaining seedlings are ravaged by insects or other acts of nature.
Seedlings should be thinned out when they have 1-2 sets of true leaves.
Most plants attain a height of 2-3" by that time and are generally easy to grab hold of and pull out of the ground. Thinning out in the early evening allows the remaining plants time to acclimate before being exposed to the heat and direct sunlight. Thinning while the soil is moist will also make it easier pull just the excess plants while leaving the healthier ones undisturbed.
Some sub varieties of various cultivars may differ slightly, the seed packet should list optimal spacing.