Environmental factors such as temperature, light, pH, and soil moisture are known to affect seed germination (Chachalis and Reddy 2000; Taylorson 1987).

Light isn’t strictly necessary for germination in most plant species. However, some seeds germinate best in absolute darkness, and others perform well with continuous sunlight. Light does become vital for every species after germination, because the initial sprout will not survive if it cannot reach a light source.

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 on the soil is not necessary for seed germination because warmth, water, and oxygen are the only conditions necessary for a seed to germinate.

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.

Contrary to popular belief on how to germinate seeds, sunlight is not a standard factor that influences seed germination (unless otherwise stated on the seed packet). In fact, sunlight can do more harm than good, as it may overheat the seeds and seedlings, killing them.

Tomato seeds can be sown directly outdoors but may not have enough time to grow to full size and produce, depending on your climate. Seeds don’t need light to germinate, although after germination, you should ideally give the seedlings 14 or more hours of light a day.

The primary reasons for failed germination are: Seeds get eaten – mice, voles, birds, and wireworms all eat seeds. Seeds need specific conditions to germinate – temperature and moisture can be difficult to control beneath the soil, and are easily affected by weather, human error, and other factors.

To germinate tomato seeds on a paper towel, wet the paper towel until it is damp (not soaking wet). Then, lay out the tomato seeds so that they are separated (not touching). Be sure to keep the paper towel and seeds in a warm place, to encourage faster germination and higher germination rates.

65° to 85°F

The fastest germinating seeds include everything in the cabbage family – bok choi, broccoli, kale, cauliflower etc, and lettuce. The slowest seeds to germinate are pepper, eggplant, fennel, celery, which may take 5+ days. The rest such as tomato, beets, chard, squash, onions, will take about 3 days.

Germination of Tomato Seeds Seeds need water, oxygen and warmth to start growing.

Soaking. Soaking is beneficial in two ways; it can soften a hard seed coat and also leach out any chemical inhibitors in the seed which may prevent germination. Anything from 1-3 hours in water which starts off hand hot is usually sufficient. Seeds of some species swell up when they are soaked.