Starting Seeds Indoors

2017-03-20 11.29.05

The article below is by Hillie Salo via the Seed Libraries Newsletter, Cool Beans!

Why not reap the benefits of starting seeds indoors? Perhaps you want an earlier harvest or need to extend the growing season. You can also produce larger and stronger seedlings that are less susceptible to insect attacks. Plus, it’s easier to monitor seedlings inside in pots than outside in the ground.
Caution: Remember that some plants, such as beans and peas, have a delicate root system and like to start and finish in the same spot. They prefer to be directly seeded, or planted in the garden, not transplanted. Other seeds, such tomatoes

peppers, and eggplants, need a head start. See the table for more plants and their preferences. You can also check the seed package for which method the plant prefers.

Get seeds from friends, neighbors, seed libraries & seed swaps or companies that sign the Safe Seed Pledge.
Don’t start seeds too early or the seedlings will become tall and spindly, or leggy. Use the six-week rule: Count backwards from the last frost date in the spring or the first frost date in fall.  However, depending on the crop, starting time may be earlier or later than six weeks. For example, warm season vegetables such as tomatoes and peppers need night time temperatures of at least 55 degrees or the seedlings’ growth will be very slow. Johnny’s Selected Seeds has a great seed starting calculator.
Seeds can be started in a range of containers from recycled yogurt cups to purchased pots, trays, or cubes. If you’re recycling your containers, clean with a 10% bleach solution: 1 part bleach to 9 parts water. When choosing a container, the most important thing is drainage, so may sure you punch several holes in the bottom of those yogurt cups.
Special seed starting mixes can be useful because they are lighter than potting soil, but they are not necessary; many people find success starting seeds with potting soil that is not full of clumps. However, soil from the garden (or those bags labeled “garden soil”) are too heavy for starting seedlings in pots.
You can select from several brands of commercial seed starting mixes. Most of them contain some variation of the following ingredients:
  • – Coir or peat moss (the base)
  • – Perlite (helps soil drain faster) and vermiculite (increases aeration and moisture retention.) Some mixes contain sand.
You can also make your own. Explore the links below for different recipes.


Plant seeds close for germination, then transplant the seedlings into pots after its true leaves appears. (First, you’ll see cotyledons, or the embryonic leaves, not the true leaves.) Planting seeds close saves space, both in your containers and especially on the number of heat mats or warm spaces. For example, for pepper or tomato seeds, consider a grid of seeds 3 X 3 or 4 X 4 in a 4 in pot.
Small Seeds
  • Fill pot with soil, tap to settle.
  • Make indentations for seed: 1/8″ for lettuce, 1/3″ for tomato.
  • For tiny seeds such as lettuce sow 3-4 seeds in each hole. Try to put no more than 2 tomato seeds in each hole as you’ll just have to untangle them later, which could damage the delicate root systems.
  • Cover seed lightly with seed starting mix or vermiculite.
  • Water from the bottom, not the top, and drain.
  • Cover pots with domes, plastic, or glass because high humidity can help with germination. The covering keeps the top of the soil moist, and keeps it from crusting over. Remove as soon as seedlings appear!
Large Seeds
  • Fill with soil, tap to settle.
  • Make 3 holes for seeds, 1″ deep.
  • Sow 1 seed per hole.
  • Cover seed with soil.
  • Water from the bottom, not the top, and drain.
  • Cover pots with domes, plastic, or glass.


To germinate, seeds need warmth and moisture. (For some seeds, exposure to or exclusion from light can be important, but most of the time, seeds don’t need light until they germinate. Until then, water and temperature are more important.)
Although each plant cultivar has a maximum or minimum temperature needed for germination, most seeds will germinate at room temperature, just faster
and stronger with a little heat, especially summer vegetables. For example, tomato seeds will germinate well when the ambient temperature is anywhere from 70 to 95 degrees, but the optimum temperature for germination is 85 degrees. Lettuce, on the other hand, prefers a cooler germination range between 40 and 80 degrees, with an optimum temperature of 75 degrees. (See the table from PennState for specific germination needs of various seeds.
Find a warm place in your house such as the top of the fridge. Remember that most heat mats will raise the temperature about 20 degrees above the ambient temperature, not to a specific temperature unless you add a thermostat. Don’t use a heating pad for humans as they aren’t designed for continuous use and/or use near water.
Moisture is important because it softens the seed coat and starts the swelling of the seed.
Check moisture daily. If container are on heat mats, you’ll want to check heat and moisture levels several times a day. Keep soil evenly moist, but not soggy. Avoid watering from above unless you have attachment that allows a light sprinkle. Instead, water from the bottom so you won’t disturb the seed. Place the seed containers in a shallow tray with water and allow them to absorb water by osmosis. Don’t leave them sitting too long in the tray. How well watered a pot is can be judged by weight. Get to know how heavy a well-watered container should feel.


No fertilizer is necessary from the time seeds are planted until they begin to germinate. Everything a plant needs to grow is contained in the seed itself! After the first seeds sprouts, remove any covering. Seedlings need the same care as seeds – right amount of water and right amount of temperature – plus seedlings need light, good air circulation and possibly a little fertilizer.

Once seeds sprout, the heat mat can be removed; though some like it warmer and can stay on heat mats (peppers and eggplants). In general, seedlings grow stronger and sturdier at cooler temperatures, 65-70 degrees daytime and 55-60 at night. Higher temps tend toward too much growth.
Air circulation
Good air circulation is necessary for disease prevention. Thin seedlings if too crowded. Brush seedlings with a hand to strengthen stems (simulating wind) or use a small fan.
Insufficient light causes weak, leggy growth. Window sills are not enough. Indoors, seedlings grow best under fluorescent lights. A standard 4-ft shop light fixture with cool white bulbs is adequate. Place the light 1 to 2 inches above the seedlings. Use a timer to leave the lights on 14 to 16 hours a day. Move the lights up as the seedlings grow. Or use boards, old books, or bricks to raise trays of plants if the lights aren’t adjustable.
Fertilize if seedlings are in pots for longer than 3-4 weeks. Use soluble fertilizer at half strength.
Continue to monitor moisture and bottom water. Let the top crust of the soil dry out before watering again.
Hardening off
Plants that have been sheltered inside need to grow accustomed to conditions outdoors before they move there permanently. Take them outside a little bit each day, first in indirect sunlight such as a porch; then, increase the time and exposure to light gradually. You can also cut back on the watering and decrease the inside temperature a bit. Such “hardening off” will prepare you seedlings for your garden.

You can find much more wonderful information at the Seed Libraries website. Thank you Hillary for the wonderful article and to Richmond Grows for the plentiful resources for seed savers and seed libraries across the country.

Don’t forget about the 10th Annual Seed Swap Saturday, February 2nd in downtown Chico!!

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