This list has been developed over many years as a guide for seed germination of annual flowers and perennials grown as annuals that we have grown at the Georgeson Botanical Garden. These guidelines have been refined to adjust to our unique conditions in the greenhouse and in the garden. Your own growing conditions, especially light levels and temperature will be unique. Use this information as a starting point for your own list and take notes on germination rates and times to determine appropriate timing for your conditions. Plants that are too large at transplanting suffer greatly from transplant shock and may not bloom the entire season, and those that are too small may dry too quickly, succumb to competition by weeds, and not become established before season's end. The calendar is timed for a field planting date of June 1. Check the chart for sowing of direct-seeded crops such as scarlet runner beans.

Some seeds require pretreatments to germinate. Treatments may include cold stratification which involves sowing seeds in a seed starting mix, moistening the mix, sealing the container in a plastic bag, and putting in the refrigerator (approx. 40F) for the required amount of time. Never allow the mix to dry out once the process is started. Move to the greenhouse, and water well as required. Scarification involves rubbing the seeds on medium sandpaper or an emery board until the seed coat is penetrated. Be careful not to destroy the embryo, just the seed covering. It takes a bit of practice and a good eye (or magnifying glass) to make sure the rubbing does not go too far.

Growing seedlings in the greenhouse or indoors is usually a two-stage process: sowing and transplanting. For most flowers, we sow seeds into 4-inch pots (up to 50 seeds per pot depending on the size of the seed) or sow them singly into plug trays containing a very fine, sterile, peat-lite seed starting mix. We use additional seed starting mix or fine, horticultural grade vermiculite to cover seeds except those requiring light, so they are surrounded by moisture. We moisten the mix, cover the pots with clear plastic, and germinate them beneath lights with a thermostat-controlled heating mat beneath the pots to provide the optimum temperature. One pot holds a thermometer so we are measuring the medium temperature, not the air temperature. You can grow seedlings in cool rooms as long as the medium temperature is optimum.

As soon as seedlings are large enough to handle, we allow the peat-lite mix to dry a bit then gently tease apart the seedlings and transplant them into cell packs (six packs) or larger pots using a coarse, peat-lite growing mix. In the table, assume the seedlings go into cell packs unless stated otherwise. The fine seed starting mix provides the best medium for germination of seeds but is too fine for continued growth. Seedlings easily rot if kept in this mix too long.

Some seedlings do not tolerate transplanting, so we have a one-stage procedure.  We skip the seed starting mix and sow them directly in cell packs using the growing mix. They include bishop's flower, corn parsley and tassel flower among others. All seedlings are grown in a well lighted cool greenhouse, approximate minimum temperature 60-65F unless stated otherwise,  until ready to move outdoors.

One week before the planting date, we begin hardening off the seedlings. Hardening is a process of gradually exposing the seedlings to strong outdoor sunlight and cool temperatures. We set the flats outdoors for 1 hour on the first day, 2 hours, the second, then 4, 6, 8 and 10 hours on subsequent days. After that, the seedlings stay outdoors until transplanting.

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