Most seeds germinate best under dark conditions and might even be inhibited by light (e.g., Phacelia and Allium spp.). However, some species (e.g., Begonia, Primula, Coleus) need light to germinate (Miles and Brown 2007). Don't confuse seed light requirements with what seedlings need. All seedlings require sunlight.
Light is not necessary for a seed to germinate, no. The majority of seeds grow most effectively in the dark. Light, which is essential for seedling growth, may actually hinder the germination process. The three primary and necessary conditions for a seed to germinate are water, oxygen, and temperature.
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.
In case the germination takes place in the darkness, the following consequences will occur: Seeds will not germinate well in absence of light. Light decomposes the carbonic acid gas, and releases oxygen, utilizing the carbon. This causes a hardening of all the parts of the seed, thereby preventing vegetation growth.
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.
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.
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.
Most of the seeds germinate best in dark environments. The presence of light tends to inhibit their growth. The light decomposes carbonic acid gas and expels oxygen which leads the seed to harden. These gases are key factors that promote germination.
Most seeds will not germinate without sunlight and will perform best with 12 to 16 hours each day. Indoors, place seed containers in a sunny, south-facing window and give the container a quarter turn each day to prevent the seedlings from overreaching toward the light and developing weak, elongated stems.
Cloddy and compacted soils that are high in clay will inhibit seed germination and emergence. Soils with a lot of plant residue in the top four inches and soils that form a crust when dry may also prevent effective germination and emergence. Seeds need air and moisture to germinate.
Bioactive gibberellins (GAs) promote seed germination in a number of plant species. In dicots, such as tomato and Arabidopsis, de novo GA biosynthesis after seed imbibition is essential for germination. Light is a crucial environmental cue determining seed germination in some species.
Germination is induced most commonly through the imbibition of water at a species-specific temperature. Imbibition of dry seeds activates a series of events (Bewley, 1997) including oxidation, degradation, and mobilization of accumulated reserve components (Penfield et al., 2005a).
First, true enough, light isn't necessary to germinate most seeds: the majority are perfectly capable of germinating in complete darkness. But there is a significant proportion of seeds that will not germinate if they aren't exposed to light. This includes maybe a third of the plants we commonly grow from seed.
Seeds of many species germinate equally well in light and darkness, and others have been found to germinate to higher percentages in light, while a smaller proportion germinate better in darkness (Baskin & Baskin 2001; Fenner & Thompson 2005; Rana et al., 2012).
Place the seeds in a warm location.
Check the seed packets to understand the ideal soil temperature for each plant. Then place the seed tray in front of a windowsill that receives partial sun, or place the seed kits on a heating mat to maintain an even temperature and light. South-facing windows generally work well.
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.
Light intensity can cause severe damage to your seedlings to the point where they die or are stunted.
Will grass seed germinate on top of the soil? Yes; in fact, germination will suffer if too much soil is placed on top of the seeds. The experts at Jonathan Green recommend placing a thin layer of mulch or topsoil over them to help keep them moist and warm and promote growth.
Different seeds have different germination requirements. The relationship between light and plant growth is complex. Some seeds will germinate only in light, some in darkness and for some the requirement for light is related to the temperature.
Seeds require a certain temperature in order to germinate. Each plant has a specific optimum and a range within which germination will occur. The closer the temperature is to optimum, the quicker germination will occur. Most seeds germinate when the soil temperature is between 68° and 86°F.
For seedlings, LED grow lights should generally be mounted between 24-36 inches above the plant canopy – however, this depends on the power (wattage) of the light source.
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.
Myth #14: LED Lights Can't Damage Plants
The reality is that modern LED grow lights can produce a very high level of light and it can cause photo-bleaching and burn leaves. This depends very much on the plant, but a PPFD of 800 is enough to damage some plants.