How to raise annuals from seeds sown indoors

Many plants that need a head start in our northern climate can be started indoors. The requirements for success in starting seeds and growing seedlings indoors are adequate light, a sterilized growing mixture, and the proper temperature. Here are some tips to help you grow your annuals successfully with seeds grown indoors.

In the home, light is often the limiting factor. Even a window facing south does not have the intensity of a greenhouse's overhead light.

• Where natural daylight is nonexistent or insufficient, two 40-watt fluorescent tubes (four are even better) set about 15 centimetres (six inches) above the plants will provide adequate light.
• An indoor temperature of 21° to 24°C (70° to 75°F) serves to germinate most seeds, but seedlings grow better at 10° to 16°C (50° to 61°F). Too high a temperature, especially when coupled with insufficient light, results in weak, spindly seedlings that will be difficult to establish when transplanted to the garden.

Sow seeds in flats or pots, or use a presown container. It can be helpful to use a commercial seed-starting mix, which usually consists of peat moss, vermiculite, and/or perlite. Seedlings will require transplanting to a compost-based soil mix once they have developed one or two sets of leaves.

1. Sow the seeds in rows, particularly when several kinds are grown in one container, or scatter them thinly. Sowing too thickly necessitates transplanting when seedlings are too small to handle easily.
2. Barely cover the seeds with the growing mixture.
3. After sowing and covering, gently mist the flat with water.
4. Cover the container with glass or clear plastic; inspect frequently.
5. At the first sign of germination, remove the cover.

Seedlings need to be transplanted, either when they become crowded or when they reach the proper size.

Seedlings are large enough to be transplanted when they have grown three or four true leaves, not counting the first pair of seed leaves. Larger seedlings can be transplanted, and although they are easier to handle, wilting is apt to be severe, and growth slowed.

1. Make certain that the soil is moist so that the seedlings can be lifted out easily with some soil clinging to the roots. Avoid pulling them out, as this can damage the fine roots.
2. Loosen the seedlings with a label stake, then hold those to be lifted with one hand; at the same time, use the fingers of your other hand to press the soil down on each side of the seedlings that are to remain.
3. Water the remaining seedlings to resettle the soil.
4.  As the plants grow, avoid any check in their growth by making sure that the soil stays moist.

Whenever seedlings or even mature plants are moved outdoors from the house or greenhouse, they need a short period of acclimatization because light intensity and outdoor temperatures are quite different from indoor conditions. If this is not done, the seedlings will be severely set back, and may even be killed.

1. A cold frame is the ideal place for this transition. The containers of seedlings can be set directly into the frame.
2. Pay careful attention to watering and ventilating.
3. On cool nights close the frame, but open it again as soon as the sun strikes it in the morning to prevent overheating.
4. Gradually increase their exposure to cold and plant out after about seven to 10 days.

If you don't have a cold frame, similar acclimatization is accomplished by setting the containers of seedlings outdoors for an increasing amount of sun each day and by taking them in at night whenever the night temperature falls below 10°C (50°F). After a week of hardening, seedlings can be transplanted into their permanent site.