Many vegetables have small seeds that are difficult to sow one at a time. As a result, you invariably end up with too many small plants close together, fighting each other for the same space, air circulation, and nutrients. In the case of beets, multiple seedlings almost always arise from each seed (which is really a clump of 4-6 seeds).
Here is a list of vegetables that often need to be thinned out:
- Carrots and parsnips
- Lettuce and other greens
- Turnips and rutabagas
- Various herbs, such as basil and cilantro
For greens and herbs, simply pull the plants out by the roots. You can use these plants whether they are big or small.
For very young root vegetables, snip the tops off the extra plants; they will die back naturally. Throw the tops into the compost.
For older root vegetables, wait for a day when the soil is quite wet, and slowly pull on the tops until the root emerges. Keep a small spade or stick handy to gently dig out the root should the tops break off, leaving you nothing to pull. Ideally, though, you should minimize disruption to root vegetables. Carrots, for example, may fork is moved (although their shape does not affect their taste). I gently pack the soil back around the side of the carrot that is bared when its neighbour is pulled.
Leave enough space for each plant to grow comfortably without pressing up against any others of its kind (or any other neighbours). This will vary according to the type of plant.
Want to reduce the amount of thinning you have to do? Try making your own seed tape. Although you may find more gaps in your garden (where seeds along the tape did not germinate and did not have backup seeds to fill in), at least you will have less precious seedlings to pull.