Growing Seedlings Indoors for Flower and Vegetable Gardens

Seeds have a few basic requirements if they are going to grow into healthy, vigorous garden plants. Luckily, they are simple and fairly easy to satisfy. First is adequate light, followed by water, warm soil, good air circulation, and food.

Let There be Light

Most seeds don’t need light to germinate, but once they’re up and growing make sure your seedlings receive 16 hours of light daily. Give seedlings too little light, and you’ll end up with spindly, leggy plants. Seedlings can tolerate up to about 18 hours per day.

While it is possible to produce healthy seedlings on windowsills, most gardeners start seeds in winter when days are short. For this reason using artificial light or supplementing natural light is best. A simple shop light‚Äîideally connected to a timer to turn it on and off automatically‚Äîis a good place to start. Ordinary fluorescent lights are fine. More expensive grow lights don’t necessarily produce better seedlings.

Whether you have a single fixture or a plant stand with tiers of lights, use chain and S hooks to hang the lights and make them adjustable. To give seedlings maximum light, adjust the fixtures so the bulbs remain 3 inches above the leaves. After the first few weeks, raise the lights and keep them 4 to 6 inches above the leaves.

Moisture and Warmth

Seedlings need even soil moisture and high humidity, but remove any plastic covering seed flats as soon as seedlings appear. Otherwise, damping off, which rots the stems at the soil line, can develop. Running a small fan ensures good air circulation and further reduces problems with damping off.

Temperatures between 60¬∞ and 70¬∞F suit most seedlings. Temperatures above 75¬∞F usually result in leggy, weak seedlings. Plant preferences vary, though, so check seed packets for recommendations. Lettuce, cabbage, and other cool-season crops prefer cooler temperatures. Soil that’s slightly warmer than the air speeds germination and growth. The easiest way to provide this is to set plants on a heat mat specially designed for growing seedlings.

For best results, check your seed flats daily. Most seedlings need evenly moist soil that is never too wet or too dry. Letting the soil surface dry out slightly between waterings helps reduce problems with diseases like damping off, but be sure to check seed packets for individual requirements, since some seedlings require constant moisture.

To determine if seedlings need watering, stick a finger into the soil or lift the flat to see how heavy it is. (Once you’ve lifted a newly watered flat, along with one that hasn’t been watered for a couple of days, you’ll be able to judge how much a flat weighs when it needs watering.)

When pots do need watering, water gently and use warm water, since cold water can shock the plants. It’s easy to flood seeds and newly germinated seedlings right out of the pots. Use a watering can with a rose that delivers a fine sprinkling of water or deliver water gently out of a water bottle with your thumb covering most of the opening. Watering pots from below is actually best, since it protects seedlings and helps prevent disease problems. To water from below, set pots in a larger container or flat filled with water, and let the water soak up to the soil surface.

Food for Seedlings

Seed leaves, the first set of leaves a seedling produces, provide all the food the plant needs to germinate and grow until the first set of true leaves appear, which resemble the mature leaves of the plant. If you are growing in seed-starting mix, once plants produce a set of true leaves, water them weekly with a liquid fertilizer such as fish emulsion mixed at half the recommended strength. After 3 weeks, switch to full strength. Seedlings growing in ordinary potting soil or a mix that includes compost may not need feeding for several weeks. Feed them if the leaves seem to turn yellow.

Raising Seedlings Right

Once your seedlings are up and growing, clip off all but the healthiest one in each pot with scissors. Or, transplant them to individual pots. Otherwise they compete for space and nutrients. When transplanting, handle seedlings by holding a leaf, never the stem, since it’s very easy to crush. To ease their transition to the garden, harden them off first by gradually exposing them to more direct sun and outdoor breezes. Start by setting plants out for an hour or two in a protected spot. Over a few days extend to leaving them out overnight. Water thoroughly before and after moving plants to the garden. Ideally, transplant on a cloudy or rainy day or shade plants with upturned bushel baskets or burlap suspended on sticks to further ease the transition to the garden.