So you've done the hard work. With swelling pride you admire the hundreds of beautiful seedlings that now carpet your patch. Unfortunately, it's time to pick winners. Culling seedlings is an essential skill for maintaining and growing a healthy garden, and you cannot be sentimental about it.
If you did a good job planting seeds and watering (we know that you did!), the resultant seedlings will inevitably start to crowd one another. The informed gardener understands that mature plants will need their space and, like buying large shoes for a growing child, you must thin your seedlings so that the remaining plants may grow into the space.
It's important to thin the plants early, before the roots become intertwined. The above image shows two kale seedlings that have been allowed to grow too long. The removal of one plant will damage and possibly kill the other, while leaving them together will mean they are in constant competition for water and sunlight. By getting to the seedlings early, you can avoid this dilemma and allow the plants to reach their full potential.
These beetroot seedlings are just the right size to separate. They are healthy and thriving, yet not large enough to have extensive root systems. Pinch the seedling you wish to keep, holding it firmly but not crushing it. With the other hand, grab the adjacent seedling, lightly jiggling and pulling the runt from the ground. Be tough, shut your eyes if you have to... it will get easier.
Some gardeners like to cull in several stages. For large plants such as tomatoes and zucchini, the informed gardener will cull when seedlings are very small and then again when they start to sprawl and interfere with one another.
Be as sentimental as you want once the seedlings are out of the ground. In many cases you may be able to offer them to friends or neighbors, particularly plants that undergo multiple rounds of culling. Whether you sing a song and put a candle in your window, or simply toss the seedlings in the compost, the important part is that each plant is given the best opportunity to thrive.