Looking Ahead: Growing Your Own Vegetable Garden Transplants

(Author’s Note: While growing your own vegetable garden transplants from seed begins in early spring, the gardener needs time to accumulate all of the necessary supplies. With this need in mind, I offer the following advice on growing your own.)

Seedlings under lights 3For gardeners interested in growing transplants of heirloom vegetables – those flavor-rich varieties found only in specialty seed catalogs – and those who believe that home-grown transplants of any ilk are far superior to nursery-grown, the gardening season starts in March with the first round of seed-sowing. There may be three feet of snow outside, but on a table somewhere in the house (or in a heated greenhouse if you’re lucky) will be plastic trays under fluorescent lights, only two inches of space between the bulbs and trays of damp soil. The lights are hung from chains on frames made of PVC pipe and you keep them two inches from the developing leaves, raising the lights as the seedlings grow.

So begins three months of indoor gardening, of watering, fertilizing, transplanting, adjusting lights, moving trays of plants to and from the outdoors, until finally the sturdy little transplants are set out into the garden beds. When asked why you are going to all of this effort when the garden centers will soon be filled with ready-to-plant transplants, you give the only honest answer. Either start gardening indoors in March or go insane.

Scheduling

Backward planning is the key. Identify the last frost date for your garden site and then schedule seed sowing dates based on the pace of seed germination and seedling development for each crop. For example, seeds of onions and pepper need a long time to germinate, so you should sow onion seeds indoors in early March, peppers eight weeks before the setting out date. Producing sturdy tomato transplants, on the other hand, takes only five to six weeks from the sowing date.

Despite the incipient insanity, don’t start too early! You will end up holding garden-ready plants under the lights, waiting for warmer weather. The end result are pot-bound and leggy plants with reduced vigor in the garden.

For our garden in Ellsworth, I assume May 31 as the zero frost date, the date by which there is little chance for a frost. With this date in mind, seeds are sown according to the following schedule (typically on the weekend closest to the date shown).

Sowing Schedule for Growing Vegetable Transplants from Seed

Ellsworth, Maine, is in USDA Hardiness Zone 5. Gardeners in Zones 3 should add two weeks to the earliest sowing date, those in Zone 4 should and one week. In Zones 6 and 7, subtract one and two weeks, respectively. For each crop, data entries include (left to right) earliest sowing date, approximate seed germination time (days), and optimum soil temperature (F).

Basil: Apr 26, 7-10, 65
Broccoli: Mar 26, 7-10, 70
Cabbage: Mar 12, 4-10, 70
Celery: Mar 30, 9-21, 65
Cauliflower: Mar 26, 7-10, 65
Cucumber: May 15, 6-10, 75
Eggplant: May 1, 6-10, 75
Kale: Apr 1, 4-10, 70
Kohlrabi: Mar 12, 4-10, 70
Lettuce: Mar 19, 6-8, 60
Melons: May 15, 6-8, 75
Onions,Leeks: Mar 1, 7-10, 65
Parsley: Mar 15,12-28, 65
Peppers: May 1, 9-14, 75
Pumpkins: May 15, 4-6, 75
Squash: May 15, 4-6, 75
Tomatoes: May 1, 6-12, 75

Sowing Seeds

Basic materials for sowing seeds include (left to right): "10-20" flats for holding seed trays and cell packs, seed trays, and cell packs.

Basic materials for sowing seeds include (left to right): “10-20” flats for holding seed trays and cell packs, seed trays, and cell packs.

Seeds can be sown in any two- to three-inch-deep container with drainage holes. I prefer to use small plastic trays sold at garden supply stores. They are typically 5 inches wide by 7 inches long and about two inches deep with drainage holes along the bottom edges. Six of these trays fit snuggly in a 10-inch by 20-inch plastic tray (called a “10-20 flat” by growers) without drainage holes. This system allows you to carry six seed trays at a time and to water them from below by simply lifting one seed tray and pouring water into the flat to a half-inch depth.

With careful handling and storage, the seed trays and flats will last for several years, easily cleaned after each use with soap and water, then sterilized with a 10% solution of household bleach. This sterilization process helps prevent seedling diseases.

After sowing, the seed trays should be covered to prevent drying out. A heating mat under the flat will maintain optimum soil temperature for uniform germination.

After sowing, the seed trays should be covered to prevent drying out. A heating mat under the flat will maintain optimum soil temperature for uniform germination.

Seeds planted in cold, wet soils tend to germinate slowly if at all. To maintain soil temperatures in the optimum range (see above table), invest in a heating mat to place under the flats. Both heating mats and soil thermometers are available from mail-order garden supply houses or your local garden center.

Fill each seed tray with a sterile growing mix that includes a starter nutrient charge and a wetting agent. I use either Fafard #2 potting soil or Pro Mix. Wet the mix ahead of use to the moisture content of a wrung-out sponge. After filling each tray, gently water the soil to settle it within the tray.

After filling a seed tray with germinating mix, make shallow furrows with a pencil.

After filling a seed tray with germinating mix, make shallow furrows with a pencil.

Sow seeds in rows within the seed tray. Typically I make three evenly spaced rows down the length of the tray, the depth of the rows twice the thickness of each seeds, and space the seeds within each row according to seed packet directions.

Seeds should be sown as evenly spaced as possible in each furrow and covered with a thin layer of a fine-textured germinating mix.

Seeds should be sown as evenly spaced as possible in each furrow and covered with a thin layer of a fine-textured germinating mix.

After placing the seeds in each row, cover them to the required depth with a thin layer of fine-textured germinating mix such as Ready-Earth. Particles in the courser growing mix can impede germination when used to cover small seed. Sifting Pro Mix or Fafard #2 through a kitchen strainer will produce an excellent fine-textured covering for seeds.

Remove the cover and turn off the heating mat as soon as seeds germinate.

Remove the cover and turn off the heating mat as soon as seeds germinate.

Label each seed tray and cover each flat with a loose layer of clear plastic (shrink wrap works well) to maintain uniform moisture in the seed trays. Once the seeds have germinated, remove the cover and the bottom heat.

Growing Seedlings

Provide supplemental lighting as soon as the seedlings emerge; window light alone is too low in both duration and intensity, and the day-night temperature fluctuation at the window sill is too extreme. Standard fluorescent tubes are adequate, although some growers prefer using one cool white and one warm white bulb in each fixture. Keep the lights on for 14 hours each day, maintaining the tubes 2- to 4-inches above the growing seedlings.

Once the seeds germinate, be careful not to keep them too wet; let the surface of the soil dry between watering. When you do water, use a half-strength solution of water-soluble fertilizer to provide essential nutrients.

Once the seedlings have produced the second set of true leaves, they can be transplanted to individual pots. I prefer to transplant into cell packs, each consisting of six small individual plastic pots. Six cell packs come linked together in a sheet that will fit the 10-20 flat, but you can separate them into individual 6-cell packs as needed. When the plants are ready to be transplanted into the garden, they can be easily lifted out of the individual pots.

When transplanting, lift and handle seedlings gently by their leaves, never by the tender stems. A seedling can survive the loss of part of a leaf, but cannot survive a crushed stem.

While plants are growing in the pots, keep them under the lights, watered and fertilized in the same manner as the seedling trays. Do not over-water! This is the most common cause of seedling diseases and can be avoided by allowing the surface of the soil to dry before watering. When watering, use a fine spray or water from below to avoid damaging tender young seedlings.

Seedlings ready for hardening off outdoors

Seedlings ready for hardening off outdoors

Before transplanting your seedlings to the garden, they must be hardened off with a slow transition to outdoor conditions. Begin by setting them outside (temperature above 45 degrees) in partial shade for 1 or 2 hours per day, gradually increasing both the light and the length of exposure over a one-week period.

All of the supplies mentioned above can be obtained at either your local garden center or from Gardener’s Supply Company (http://www.gardeners.com/buy/seed-starting-and-lights/seedstarting-kits/).

In next week’s column, I will offer a sowing schedule for transplants of flowering annuals and a look at new vegetable and flower varieties for 2015.

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About Reeser Manley

I was born in Laramie Wyoming but moved to the southeast at an early age. I was educated through my B.S. in Biology in the Columbus, Georgia area, then crossed the Chattahoochee River to earn my M.S. in Botany at Auburn University. For the next ten years, I worked as Horticultural Manager for the George W. Park Seed Co. in Greenwood, S.C. At 40 years of age, I decided to return to graduate school and in 1994, I earned a Ph.D. in Horticultural Science from Washington State University, Pullman, Washington. Fast forward through 10 years at university (7 at UMaine, Orono) and you find me teaching high school science in Eastport, Maine, the edge of the world, and writing a weekly garden column for the Bangor Daily News. My new book, The New England Gardener's Year, a Month-by-Month Guide for Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, Connecticut, and Upstate New York”, will be published later this year by Cadent Publishing. You can learn more about the book by visiting its Facebook page: http://www.facebook.com/pages/The-New-England-Gardeners-Year/187285218055676.)