Indoor gardening: It’s seed-starting time

By Dawn Pettinelli - UConn Home & Garden Education Center
Feature Article - posted Wed., Feb. 8, 2012
- Contributed Photo

There are many advantages to starting your own seeds indoors. Not only is it the most economical way to fill your gardens with flowers and vegetables, but many new, rare or heirloom varieties can only be purchased as seeds.

Seeds can be started individually in cell packs or other small pots, which often eliminates the need for transplanting, or as a group in a single flat or shallow container. This latter technique works best for very tiny seeds which would be difficult to plant individually, like leeks or snapdragons.

Whichever method you decide on, start with clean containers and a sterile, seed-starting medium. The particles in seed-starting mixtures are generally finer than those found in regular potting mix. Sometimes they contain added nutrients for plant growth, as well.

Although you could water the seeds after planting them, I find it much easier to place some seed starting mix in a clean, plastic bucket and add warm water before planting. Keep adding water and mix with a trowel until the medium is thoroughly moistened but not saturated or soggy.

Fill your containers up to about a quarter inch below the rim and firm lightly. Keeping the potting medium near the rim increases air circulation and reduces the chances of seedlings being killed by the damping off fungus.

Poor germination is often due to planting seeds too deep or overwatering. Most small seeds are simply pressed lightly into the medium. Many seeds, like petunias and nicotianas, require light for germination. Larger seeds, such as zinnias and tomatoes, benefit from a light covering of planting mix. A few seeds including pansies and sweet peas need total darkness for germination.

After sowing your seeds, either place your flat or cell pack in a larger flat with a clear plastic dome or in a clear plastic bag until signs of germination are evident. The plastic keeps the potting medium moist and creates a humid atmosphere. Most seeds germinate best at about 70 degrees F. Heat placed under the seeds speeds the germination of many species. Serious seed starters often purchase heated seed mats for bottom heat.

Newly-emerged seedlings need light to develop into healthy, stocky plants. Plants may be set on sunny windowsills, or better still, under artificial lights. The wide spectrum lights are preferred and they should be positioned just a few inches above the plants. The lights need to be adjustable so they can be raised as your plants grow. Fourteen to sixteen hours of light each day is recommended.

Seedlings can be transplanted if necessary when they get their first set of true leaves or when they are large enough to be handled. A regular soilless potting mix may be used and should be moistened before using. After filling new pots with the moistened mix, make holes for each seedling using a pencil or chop stick. Then with a spoon or chop stick, lift individual seedlings out of their flat grasping a leaf gently. Set them at the same depth they were originally growing except for tomatoes and marigolds, which can be planted a little deeper as the form adventious roots.

Use a dilute (one-third strength) fertilizer, either organic or synthetic, every time you water. Initially watering is done from the bottom to avoid dislodging the seedlings, or use a hand mister or bulb sprayer.

Look on the seed package, in catalogs or in seed starting books to find out when to start certain seeds. Often it will say start 6 to 8 weeks before the last frost date, or something to that effect. Typically in Connecticut, May 15 is considered a reasonable last frost date. It might be before that in southern parts of the state and a little later in northwest areas. Always check the forecast before planting your seedlings in the garden. Also, they should be gradually hardened off before they get transplanted into their permanent outdoor homes.

For answers to questions about seed starting or any other gardening query, call the UConn Home & Garden Education Center (toll-free) at 877-486-6271, visit, or get in touch with your local Cooperative Extension Center.



It is misleading to give the impression that Sweet Pea seed will not germinate in daylight. When I fail to harvest a pod in time it scatters seeds around the glasshouse and some of them germinate where they lie. If there are children around it is better to bury the seed, since Sweet Pea and most other Lathyrus species are somewhat toxic and can give rise to lathyrism. For this reason it is dangerous to use the title Sweet Pea when referring to culinary peas.

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