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Seed Starting Supplies

Seed Starting Basics
Seed starting supplies
Bio-degradable pots and trays for seed starting.

It is easy to grow your own plants from seed. By starting your own seedlings you can choose from hundreds of varieties that are not available in garden centers. The cost of plants will be far less than those sold in nurseries. You can also have transplants ready to go into the garden at any time you choose.

Here are the essentials for seed sowing indoors: containers, seed-starting mix (not soil), light source, heat source, water, labels, and markers.

Do an inventory of your seed-starting supplies. Do you have enough containers or flats for starting seeds and transplanting seedlings? Do you have a sterile seed-starting mix? Do you have a heating mat to provide bottom heat for seed germination? Do you have adequate lighting for growing seedlings?


Choose from plastic seed-starting kits (includes bottom trays, divided plastic containers, sometimes called six-packs, and clear plastic humidity dome covers), undivided shallow wooden or plastic trays–called flats, peat or coir pots, Jiffy pellets, egg cartons, yogurt cups or cottage cheese and butter tubs (be sure to cut drainage holes in the bottom of plastic containers), or paper pots.

Make sure your containers are clean. Wash new and used containers with soap and water and rinse used containers with 10 percent bleach (1 part chlorine bleach to 9 parts water) to sterilize the containers. (Seedlings are very susceptible to disease so it’s important to disinfect containers.)

Germination Mix

Prepackaged soilless seed-staring mix or a homemade mix of 1 part fine sphagnum peat moss and 1 part vermiculite or perlite (1:1 ratio). A soilless mix should be sterile (pathogen-free), light, and loose to avoid compaction, and should absorb water easily but allow excess moisture to drain away quickly. When seedlings are ready to be transferred to a larger pot, switch to potting soil.

Labels and Markers

Wooden or plastic labels, permanent markers, pencils, crayons, or grease markers.

Grow light for seeds
LED grow light for seed starting

Light Source

Grow lights, cool white bulbs in fluorescent light fixtures, and south- or south-east-facing windows. Because few windowsills get enough light to grow seedlings, your best choice is to use a grow light or two 4-foot-long fluorescent tubes—one “warm white” and one “cool white” tube suspended in an adjustable fixture. Grow lights should be adjustable. The lights should be set or suspended 2 to 4 inches (5-10cm) above the seed-starting mix and later above the growing seedlings (again, a constant two inches above the seedlings’ topmost leaves). A light timer should be set to light the seedlings 16 hours a day.

Heat Source

Germination heat mat, heating cables or coils, soil thermometer, thermostat, warm location (such as a sunroom or a greenhouse). Most seedlings germinate quickest in warm soil (70° to 75°F/21° to 24°C); set your containers on top of the heating mat or cables and use a thermostat to switch the heat on and off automatically. Once seeds have sprouted remove the cables or set the temperature cooler (the upper 50s to lower 60sF/ 10°-16°C).

seed starting tray and bag
A clear plastic bag is used as a simple greenhouse to maintain humidity.


Use spring water, non-chlorinated tap water, or rainwater. Use a rigid clear plastic dome or clear plastic bag to maintain high humidity before germination. Use a watering can with a small-holed sprinkling head or use a spray bottle or spray wand that delivers fine droplets of water—don’t spray directly with a hose. If you are starting seed in peat pots, paper pots, or soil blocks, a capillary mat can deliver water as needed; capillary mats allow the seed-starting medium to draw or wick water from a bottom reservoir as needed; a liquid fertilizer can be added to the reservoir to feed larger seedlings.


Seedlings growing in a soil-free starting mix or lean potting mix will need a small amount of plant food when the first true leaves develop. For the first three weeks after true leaves develop, feed young seedlings once a week using a half-strength solution of fish or seaweed fertilizer, compost tea, or a liquid organic fertilizer specially formulated for seedlings. Starting the fourth week after true leaves develop, feed seedlings every 10 to 14 days using a normal-strength fertilizer solution; fertilizer will not be needed if your transplant your seedlings to a potting mix that has nutrients added.

Also of interest:

Lights to Grow Plants: Choose the Right Light

Vegetables to Seed Start Indoors

Simple Seed Starting

Seed Shelf Life

Written by Stephen Albert

Stephen Albert is a horticulturist, master gardener, and certified nurseryman who has taught at the University of California for more than 25 years. He holds graduate degrees from the University of California and the University of Iowa. His books include Vegetable Garden Grower’s Guide, Vegetable Garden Almanac & Planner, Tomato Grower’s Answer Book, and Kitchen Garden Grower’s Guide. His Vegetable Garden Grower’s Masterclass is available online. has more than 10 million visitors each year.

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