Late summer into fall is an ideal time to start root vegetables from seed. Favorites are carrots, beets and onions.
Onions do best planted by seed or transplants in the fall. If you are using transplants, it is not necessary to ensure they stand straight up. You can plant them in a 1 ½ to 2″ trench by laying them sideways. Cover the root end with earth and water. In a couple days, the seedlings will stand up by themselves.
The small onion bulbs called sets are also available but these will only develop into green spring onions if planted in the fall, they are best set out in spring if large bulbs are desired. Thin onions to 4″apart for bigger bulbs. Unlike carrots and beets, feed onions regularly, especially early in the season.
Beets are notoriously cranky about germinating. Each seed is actually a cluster of seeds in a husk. There can be as many as 6 seedlings that emerge out of each one! Because of this husk, it is best if the seed can be soaked for 24 hours prior to planting.
Amending the soil: If your soil is clay-like, you will need to amend it with a good amount of compost, Sloat Planting Mix, or Sloat Loam Builder. To all soils: Apply EB Stone All Purpose Organic (5-5-5) fertilizer and Kelp Meal (1-0-1) when the soil is prepared.
Water the bed well prior to seeding to further stimulate that husky seed to sprout. Plant the seeds deeply, about 1″ (that’s about the depth of the first knuckle on your finger). Again, thin seedlings to a gradual spacing of 2″ and eat the thinnings.
Carrots require deep sandy loam to produce long roots. If your soil is clay-like, 
you will need to amend it with a good amount of compost, Planting Mix, or Loam Builder. You may want to plant dwarf varieties such as Danver’ s Half Long if your soil is not crumbly and loose at a 1 foot depth.
Apply EB Stone All Purpose Organic (5-5-5) fertilizer and Kelp Meal (1-0-1) when the soil is prepared. Carrots love potassium which is the third fertilizer number on the box. Too much nitrogen will produce roots that have many hairy roots and fork so don’t feed regularly after they emerge as you would leafy vegetables. The seeds should be planted very shallowly as they require some UV light to germinate.
Sometimes it is best to sprinkle the seeds on the prepared surface and dust them with no more than ¼“ of potting soil or fine vermiculite. It can take up to 14 days for germination to occur, so be patient. You can mark your row by planting fast germinating radish seeds in front or at the sides. Once your seeds sprout and produce the first true leaves, you can begin to thin them. The carrot thinnings and the baby carrots can be added to soups. Ultimately, you will want 1″ between carrots.
Keep all root crops well watered. Do not let the soil become dry between irrigations. This will cause cracking and corkiness in roots and reduced bulb size in onions.