Seeding Vegetables Indoors

Starting Seeds Indoors - Getting a Jump on Spring Vegetables

To get a head start on the vegetable garden before the last frost date on April 15, or May 1 in some Sonoma County areas, many gardeners like to start seeds indoors or in a greenhouse. By potting them up after germination, seedlings can be ready to transplant when the weather turns warm. Here’s what is needed:

A SCHEDULE. Timing is important. Refer to the Sonoma County Master Gardener “Vegetable Planting Summary” for details on planting dozens of vegetables. (See link below.)
VIABLE SEED. Seeds have a shelf life as well as ideal storage requirements. Consult references below for fresh seed sources and varieties.
GROWING MEDIA. Commercial potting soils provide proper water filtration and aeration. Avoid filling pots with native soil that becomes compacted and often contains pathogens.
Re-used containers should be clean and sterilized to eliminate risk of diseases.
PLANTING DEPTH. Follow directions on seed packets for planting depth information, usually 2-4 times the diameter of the seed. Very fine seeds may be lightly pressed into the medium and watered in with a mister.
After seeding, keep the soil moist but not wet. Use a mister so as not to displace the seeds or place containers in a tray with one-inch of warm water in the bottom and, when saturated, set the containers aside to drain. Don’t let containers sit in water constantly or the soil may become too wet and the seeds will rot.
Once seeds germinate, place pots in a south-facing window or under fluorescent tubes or special grow lights. Plants need 16 hours each day under lights but soil dries out fast; be sure to keep the soil evenly moist.
Once seedlings are well-established and develop a second set of true leaves, fertilize them with a half-strength, soluble plant fertilizer solution.
WARM TEMPERATURE. Seedlings should be placed in a location that is about 65-70 degrees during the day and 55-60 degrees at night. Many gardeners use a heat mat set with a timer.
HANDLING SEEDLINGS. If re-potting before transplanting to the garden, use sterile containers and handle seedlings with care to avoid damaging roots. Handle seedlings by the leaves rather than by their delicate stems.
HARDENING OFF. About 2 weeks before transplanting to the garden, harden off young plants by exposing them to lower outdoor temperatures and humidity as well as slightly reducing water. Many gardeners move plants to an outdoor cold frame or shaded outdoor area during the day and bring them in at night for a week, then leave them outdoors for another week before transplanting seedlings into a sunny site.
In general, plant seedlings at the same depth they were in the planting tray. However, some plants, such as tomatoes, squash, and cucumbers can be re-potted up to the first true leaves to encourage additional rooting along the buried stem.

Additional Information

Sonoma County Master Gardener Vegetable Planting Summary.
SCMG Vegetable Seed Sources.
Choosing Vegetable Varieties.

April 2022