Starting Plants from Seeds

72 cell 1020 flats under T5 high output 6500K fluorescent lighting.

Starting plants from seed is an art, but one that can be learned. We plant thousands of seeds every year at the Garden Pool and starting plants from seeds and seed saving make it all possible and affordable. We have our own tips to share with you to make your seed starting experience successful. We hope this information helps you start your own amazing plants from seeds.

1020 Flats

We use 1020 flats (or trays) to start most of our seeds. They are called 1020 flats because they roughly measure 10″ wide by 20″ long. This is a handy size to carry and can fit a variety of cell sizes. A cell is the part where you plant the seed in the flat. A typical 1020 flat that we use holds 72 cells, but here are more sizes. You can use small pots, too.

We determine the ideal seedling transplant height by taking the 1020 tray cell diameter and multiply that by two. To find the maximum seedling transplant height, multiply the cell diameter by four. Here is a handy guide below to help you determine the maximum seedling transplant height.

Number of Cells per 1020 Flat Top Cell Diameter Maximum Seedling Transplant Height Ideal Seedling Transplant Height
38 cells 2.25 9″ 4.5″
50 cells 1.88 7.52″ 3.76″
72 cells 1.5 6″ 3″
98 cells 1.38 5.52″ 2.76″

Grow Medium

One coco brick (right) expands up to 6 times it's original compressed size! This is the perfect sustainable grow medium.

It is not a secret that our favorite seed start medium is coco coir, particularly the GP Coco Bricks. It is the best for starting seeds because it inhibits the growth of pathogens that are harmful for the seed. It is a great sustainable grow medium for aquaponics or traditional soil gardening.

Supplemental Lighting

When seeds first sprout they are in the vegetative phase of growth and can take extended light hours to help boost growth. We primarily use T5 High Output Fluorescent lights as the power usage is low and they are bright. We try to mimic the Springtime sun by using blue tinted bulbs of the 6500K (daylight) color spectrum. Place the lights as close as possible, providing even lighting coverage and not burning the plants. Rotate the plants at least once a day to make sure the plants do not bend  or stretch toward the light. Set the lights on timers for 18 hours of light and 6 hours off.

Informative Video


Recorded LIVE
Who: Dennis McClung
When: May 11th, 2013
Where: The Garden Pool in Mesa, AZ
Length: 44 minutes
This class was recorded live in a classroom setting. To be a part of our classes in person, join our meetup group.

US Extension Office Seed Start Guides

Click on your location from the list below to go to your extension office website. Once you have reached your local extension office office website, search for “planting guide” to find your local planting guide.

Alabama Iowa New Jersey Vermont
Alaska Kansas New Mexico Virginia
Arizona Kentucky New York Washington
Arkansas Louisiana North Carolina West Virginia
California Maine North Dakota Wisconsin
Colorado Maryland Ohio Wyoming
Connecticut Massachusetts Oklahoma
Delaware Michigan Oregon American Samoa
District of Columbia Minnesota Pennsylvania Guam
Florida Mississippi Rhode Island Micronesia-Kolonia
Georgia Missouri South Carolina Northern Marianas
Hawaii Montana South Dakota Puerto Rico
Idaho Nebraska Tennessee Virgin Islands
Illinois Nevada Texas
Indiana New Hampshire Utah
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