Growing Vegetables from Seed
Starting Seeds Indoors – Getting a Jump on Spring Vegetables
by SCMG Stephanie Wrightson
As the days grow longer and warmer, 4-inch pots of vegetables appear in front of stores…and our hearts race. However, in Sonoma County, the last average frost date is April 15. Many of us are sadly wise to the fact that many tender plants are far from safe if planted before May 1. Avoid buying plants now…instead, get your “gardening fix” through indoor seed propagation!
Here’s what you need:
1. A SCHEDULE. Timing is important when transplanting seedlings to the spring vegetable bed. Know when to sow seed indoors by referring to the Sonoma County Master Gardener (SCMG) Vegetable Planting Summary. Some vegetables, such as carrots, are not recommended for indoor germination.
2. VIABLE SEED. Seeds have a shelf life as well as ideal storage requirements. Since seeds are relatively inexpensive and the best seed has about a 75 percent germination rate, don’t skimp by using old seed. Refer to the SCMG Vegetable Seed Sources. If you are uncertain what varieties do well in Sonoma County, refer to Choosing Vegetable Varieties.
3. GROWING MEDIA. Water acts very differently in pots than it does in the ground. Commercial potting soils provide proper water filtration as well as adequate aeration to provide the oxygen required by germinating seeds. You can make your own potting mixture with one-third sterilized sand, one-third vermiculite or perlite, and one-third peat moss. Containers must be clean and, if reused, sterilized to eliminate risk of diseases, weed seeds and insect pests.
4. PLANTING DEPTH. Seed packets generally contain planting depth information. A rule of thumb for planting depth is two to four times the diameter of the seed. Really fine seed may be lightly pressed into the medium or watered in with a mister. Some gardeners transplant one seed in each container, while others broadcast seed in a flat of soil. If broadcasting, thin seedlings after they germinate.
5. WATER. After seeding, the soil should be kept 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.
6. LIGHT. Once seeds germinate, they need light. A south-facing window is ideal, but seedlings also can be placed under fluorescent tubes or special grow lights. If using artificial lights, keep them on about 16 hours each day. Lights can dry out soil faster; be sure to keep the soil evenly moist. Once seedlings are well-established, you may fertilize them with half-strength soluble plant fertilizer solution.
7. TEMPERATURE. Seedlings should be placed in a location that is about 65-70 degrees during the day and 55-60 degrees at night. I have a large counter next to a south-facing window that meets this requirement. Some people find that the dryer in the laundry room or garage is adequate with proper lighting.
If you must re-pot before transplanting to the garden, follow the principles above (proper soil, sterile containers, etc.) and handle the tender seedlings with care. Use a knife or wooden plant labels to gently lift the plant and roots without damaging them. Handle the seedlings by the leaves rather than by the delicate stem. In general, plant seedlings at the same depth they were in the planting tray. However, some plants, such as tomatoes, can be re-potted to the first true leaves causing additional rooting along the buried stem.
About two weeks before transplanting to the garden, “harden” your plants. “Hardening” involves acclimating the plants to the outdoor garden by lowering temperatures and relative humidity as well as reducing water (without allowing the plant to wilt). This causes thickening of cell walls and produces a stronger plant. I move my seedlings outdoors under a covered patio during the day when temperatures are at least 45 degrees or higher. Some gardeners will lower the indoor temperature or move plants to a cold frame.