Metal halide lights emit an intense, bluish-white light that is excellent for growing plants. The foliage stays green and vigorous, and plants are usually stocky and strong. Metal-halide lights are currently the number one choice for serious indoor gardeners.
Once sprouted, most vegetable seedlings and other garden plants require at least 12 hours of good light per day, along with 8 hours of darkness. However, seedlings will grow the best when provided 14 to 16 hours of light.
While many houseplants can thrive away from any direct light source, seedlings need a good windowsill or some grow lights to provide the energy they need to grow! Moreover, they are sensitive to direct sun, more so than many adult plants are, so picking the right kind of bright spot is crucial.
A sprouted seed is no longer a seed but a seedling, a miniature plant. The most important thing to consider and deliver is adequate plant light. Seedlings need more light than full grown plants, ideally as much as 16-18 hours a day. Additional light may be required for seeds started during the winter months.
Sowing seeds indoors under fluorescent lights is the easiest way for the home gardener to control growing conditions and grow healthy transplants. Incandescent bulbs give off more heat and less light (mostly red) than fluorescent tubes and will not produce good transplants by themselves.
Light intensity can cause severe damage to your seedlings to the point where they die or are stunted.
In most cases, seeds will germinate within three weeks (after that, try starting a new round of seeds). spot in your house (preferably a south-facing window). Continue to keep the mix moist, but not overly wet. Seedlings should be watered once a day or every other day, depending on how much sun and heat they get.
In contrast, blue light is considered equally effective as green or red light at driving photosynthesis. Thus, while blue light can appear somewhat dim to us, it has high energy and is useful for plant growth applications.
Red light stimulates vegetative growth and flowering (but if a plant gets too much, it will become tall and spindly). Blue light regulates plant growth, which makes it ideal for growing foliage plants and short, stocky seedlings (but too much will result in stunted plants).
A good rule-of-thumb for LED grow lights is 40 watts of actual wattage per square foot of growing space for flowering medical or "high light" plants like tomatoes or peppers.
Seedlings need 14-16 hours of light every single day, without fail. Don't leave them on for 24 hours a day though. Like us, they need to rest at night. So plan to keep your artificial lights on for 14-16 hours during the daytime, and turn them off overnight.
Leave the grow lights on for 14 to 16 hours per day to provide light for the young seedlings. It's best to turn the light on early in the morning and turn it off around dusk. Your seedlings will still thrive if you deviate from this schedule.
630-660 nm (Red) Light: This light is essential for germination and stem growth, as well as leaf expansion. It is also used to regulate periods of growth and flowering. Too much red light, or red light used alone, will produce tall plants that appear stretched with thin leaves.
Blue light helps plants produce chlorophyll, the pigment they need to grow. It also helps encourage germination and root development in young plants and seedlings. Red light regulates plant growth and helps plants produce flowers and fruit.
After seeds have sprouted, watering from above with any force is likely to knock over the fragile seedlings. This is why it's best to use a mister. With a mister or spray bottle, you have to be willing to check on your baby plants at 2x a day to make sure they don't dry out.
Until seeds have sprouted, keep the seed bed moist, never allowing it to dry out. Water with a fine-spray hose nozzle or watering can which will provide a fine misty spray and not wash away the soil. Water often enough (usually about once a day) so that the soil surface never dries out, but remains constantly moist.
This is why some LEDs give off a purple glow, unlike full spectrum lights that emulate daylight. But as we know, LEDs, like those available for home lighting, come in more neutral white colors that will also work for seed starting.
It is true that seedlings need lots of bright light to grow healthy and strong—but they also need a period of darkness in order to thrive. In general, seedlings should receive roughly 14 to 16 hours of light each day.
Telltale Signs of Too Much Light
The most apparent sign is leaf burning. This typically causes the yellowing of leaves at the top of the plant but the veins stay green, and the leaves take on a yellow or brown, burnt look.
As a rule of thumb, aim for 20 to 40 watts per square foot. Divide the wattage of your bulb by 20 (such as 400 watts divided by 20 = 20), and then divide the wattage of your bulb by 40 (400 divided by 40 = 10). The answer gives you the extremes of your light intensity range.
All seedlings require sunlight. Seedlings will become leggy and fragile and will not produce to their potential if they do not have sufficient light. Table 1. Soil temperature conditions for vegetable crop germination.
Seedlings have a natural tendency to grow toward light. When the light source is too dim or far away, the seedlings kick into survival mode and grow quickly in height to try to get closer to that light.
Typically, plants use more blue and blue-green light when they are seedlings, and more red light later on in their life cycles when they begin to flower and produce seeds.