Onion seed of both white and yellow varieties, can be sown indoors in flats, early in the spring. When the seedlings grow to 4 inches in height, they can then be carefully lifted from the flats and transplanted to their permanent places. Soil should be cultivated carefully, and all uneven clods, stones and roughage removed to allow for easy transplanting. Soil should have a liberal amount of lime to help in aeration. A fertilizer such as 5-10-5 plus well-rotted manure should help to produce a satisfactory onion crop.
As with other transplants, care should be taken so as not to damage the tender onion plant roots.
Since an onion seedling does not have much of an enlargement at the base of the stem, it is important to make sure most of the white stem end is planted along with the roots. Actual depth will of course depend on the length of the roots. Some may need to be planted 1-1/2 inches, others perhaps 2 or more inches deep. The onion transplants should stand at least 2-3 inches apart.
Moderate temperatures and adequate moisture are required to produce a good crop. The most important rule of onion culture is never to allow the soil in which onions are growing to dry out completely. The steady growth of onions should not be checked in any way.