For the same reason you don't store your bag of potatoes in a well lit place, you should not store your seeds in one. Light is another important cue to the seed that it is time to sprout. When storing your seeds in see-through glass and plastic containers, it is important to put these containers in a dark, dry place.
Plant ¼” deep and cover with vermiculite. Keep the seed and media moist by using a plastic cover over the seeding tray. Zinnias need darkness to germinate so use a black plastic cover if possible. Seeds will germinate in 4-8 days at 70-75°F.
Stratification is the process of giving your seeds a period of 'cold' to prepare them for better germination. If you dont stratify seeds, they can still germinate but the rate is often much lower and they can actually take 2 or 3 times longer to germinate.
Generally, native plants grown in cold climates will require cold stratification before you plant them in the early spring. Common seeds that require cold stratification include common milkweed, St. John's wort, and many coneflower species.
Light is required for some lettuce seeds to grow. When seeds fail to germinate in the dark, they're called “photosensitive” or “photodormant.” Once they do emerge, to grow a field of lettuce with heads that are all relatively the same size (uniform), the seedlings must all spend an equal amount of time in the sun.
Germination Conditions
Tomato seeds do not need light to germinate, but they do need proper warmth and moisture. Temperatures around 70 degrees are ideal. Temperatures between 50 and 75 also work. Tomato seedlings prefer well-draining sandy loam soil at a pH between 6.0 and 7.0.
Zinnia seeds do not require any treatment (eg soaking, stratification) before sowing. Zinnia seeds can be sown directly into the garden OR seedlings can be raised in trays or other containers and transplanted to the garden once established.
Your seeds will require dark to germinate, so they must be planted at the appropriate depth. For most sunflower varieties, that's somewhere between a half and three-quarters of an inch deep, but you should look up the depth specific to your variety just to be sure.
Many people soak the seeds in water for several hours before planting them to soften them. Once the seeds are planted, they need plenty of light and warm temperatures to germinate. After 2-3 days of watering the seed, you should see a green sprout pushing through the soil.
If your seeds are larger (like beans or peas) or they require darkness to germinate (check the instructions on the seed packets), cover them with a layer of vermiculite or seed starting mix equal to their height, usually 1/4 inch to 1/2 inch.
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.
It's official: beans, peas, and pumpkins are among the top ten easiest plants to grow from seed, according to a list created by the Home Garden Seed Association. Also on the list: cucumbers, zinnias, cosmos, sunflowers, lettuce, radishes, and squash.
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.
Too cold and they'll be very slow to sprout and too hot will also reduce the speed of germination. Far too cold or hot and they'll just fail. Academic research carried out in the USA has charted these temperature ranges for a number of vegetables.
– Too Much Heat or Too Cold
The tomato seed germination temperature needs to be between 70 to 80 degrees Fahrenheit. If you expose the seeds to temperatures that are off this range, the seeds won't be able to cope or germinate. If the weather outdoors is too cold, tomato seeds will not sprout.
The seeds need light to germinate, so cover them with just the very finest layer of potting soil or vermiculite. This will help to trap moisture around the seeds to prevent them from drying out. Water from below then remove pots once you can see moisture at the top. Celery seeds need gentle warmth to germinate.
Onions don't need light to germinate, but they do need moisture and warmth. I usually put ours on top of our grow shelf so the warmth from the lights below acts as a heating mat. This really jump-starts the germination process. As soon as the onions begin to sprout, get them into as much light as you can.
When planting pumpkin seeds—indoors or out—place seeds into soil one-half to 1 inch deep with the pointed end facing down. Indoors, place seed-starting pots under artificial lights or in a bright south-facing window. Pumpkin seeds germinate best in soil that's 80 to 85 degrees.
The seeds of most annual garden flowers and vegetables require no stratification. However, many trees, shrubs, perennials, and wildflowers will only germinate after their seeds are stratified.
Another tip is to not start stratification too early, if the seeds require 30 days of cold stratification, plan to stratify for 30 days, because if you stratify for 60 days that's a extra 30 days where they might get moldy. Because this is a potential issue, it's best to check on stratifying seeds every couple weeks.
Freezing and thawing:
Freezing and thawing of the seeds seems to speed up the stratification process compared to storing them at a constant refrigerator temperature.