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.
They perform important respiratory functions at night. Seedlings should have at least 6 hours of darkness per day, and more mature plants at least 8-10 hours a day.
Once those seeds sprout, proper seedling care is essential, and that includes supplying the growing plants with the right amount and quality of light. 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.
Seedling Daily Light Needs
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.
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. Affordable plant lights can be found at many garden supply stores for less than $100.
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.
Plant stems become “leggy,” meaning stems become long and thin and appear to be reaching toward the source of light. A lack of sufficient light causes the plant to grow long spaces on stems between the leaf nodes (the point where a leaf grows out from the stem).
This 100W LED light was just too close to the seedlings, causing them to get burned and turn purple and suffer, they can get burned just like we do in the bright sun! It is true that your seedlings need bright light to grow healthy and strong—but, too bright a LED light could actually damage them if it's too close!
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).
Ordinary LED shop lights work incredibly well for starting plants. When plants first go outside, as long as they are outside receiving most of a day's natural light, there is no need to supply them with additional LED lighting. Especially if you are bringing them back in at night.
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.
Plants may grow taller in a dark place for a while: They respond to the lack of light by growing "taller" and more spindly, and the plant stem and leaves may be yellow and not as leafy. The growth in the dark is caused by auxins, which are substances that regulate plant growth.
If we look at the matter from the gardener's point of view, however, we can use the rule of thumb that most cultivated plants on sale in seed form prefer to germinate in the dark.
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.
The light slows stem elongation through hormones that are sent down the stem from the tip of the stem. In the darkness, the hormones do not slow stem elongation. The seeds in the dark-grown condition rely upon the stored chemical energy within their cells (lipids, proteins, carbohydrates) to power their growth.
Seedlings should be watered once a day or every other day, depending on how much sun and heat they get. Remember that seedling roots are fairly close to the surface and they're growing in a small amount of media, so they don't need a deep soak the way larger plants do.
Location is Everything – grow lights should sit no more than 3″ above the leaves of seedlings. Anything further away will cause legginess as the plants reach for the light source. Make it Windy – plants also need a little stress to develop strong stems. Blow on your seedlings every day, or install an oscillating fan.
Vegetative Growth & Flowering
During the seedling phase, when plants are tender, lights are suspended higher. Generally, LED lights should be about 24-26 inches during this phase, and then lowered to 18 to 22 inches during the vegetative and flowering stages of growth.
For most home gardeners, a plug-in shop fluorescent or LED light fixture is the perfect type of light to use for seed starting. When shopping for fluorescent lights, look for high-output, full-spectrum (sometimes called “daylight”) bulbs.
Light color
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.
Some seeds like Allium 'Purple Sensation' and Eryngium giganteum need a long period of cold-moist stratification with alternating temperatures. These are the most difficult seeds to germinate.
All seeds need water, oxygen, and proper temperature in order to germinate. Some seeds require proper light also. Some germinate better in full light while others require darkness to germinate.
Soaking your seeds in hot water held to a specific temperature will also break down the seed coating. But this one is a double-edged sword. Soaking seeds in hot water will help speed up germination but can come at the cost of lower germination rates.