How Deep should I plant My Seeds?

Q.  If I plant turnips and beets by burying the seed instead of “broadcasting” them, how deep should the turnip seed go?  The only thing I can find on them is the latter method.
 
A.  A “rule of thumb” for planting seed is to place them in a shallow furrow and bury them 2 1/2 times the width of the seed.  Turnip seed is tiny, so they will not be covered very deep at all.  Most people end up more or less broadcasting the seed in the furrow, but do so much too close together.  Your seeds should be far enough apart that the plants do not crowd each other when they are making bulbs.  unless you plant your seeds 1 1/2 to 2″ apart, you’ll need to thin them after they are up and growing, otherwise you won’t get anything but tops.
 
The best thing you can do to assure good germination and healthy plants is to cover the seeds with sand, rather than the regular soil.  Then, keep the soil moist, but not soaking wet. 
 
And it’s important that the soil be warm.  Although turnips and beets are fairly hardy and will germinate and grow in cooler temperatures than tender crops like tomatoes and squash, they will grow faster if the soil is warm.  Consider using the “mini-greenhouses” to accomplish that for you.