What are the ideal germination conditions for herbs and leafy greens?

Question

I'm new to home gardening. I just bought Sustainable Seed Company's Herb Collection (Basil, Chives, Cilantro, Dill, Lavender, Oregano, Parsley, Rosemary, Sage, Thyme) and Mountain Valley Seed Company's Leafy Green Collection (Kale, Lettuce, Arugula, Chard, Spinach). The herb planting guide that comes with the seeds recommends the paper towel method to test the germination of the seeds. It also says,

"[Seeds] are widely variable. For example, lettuce need a temperature between 65-80°F and a good quantity of light to germinate, while peppers or other warm season crops need temperatures between 75-85°F or higher to germinate, and squash, melons, and cucumbers like the paper towel to be a little drier. Do a little research on the crop and the ideal germination conditions before starting."

As I understand, the germination conditions they're referring to are: moisture, temperature, lighting, and airflow. Am I missing any? Does pH or other properties of the water impact germination?

Is there a table or other resource, where I can look up all these "ideal germination conditions"? The seed packets themselves give some - but not all - of this information. I'm a scientist by training, and I'd like to minimize the time it takes to germinate these seeds.

Answer 1

Most seeds will do fine in fresh potting soil, I never use paper towels for germination of small herbs or vegetables. However, like you mention many factors are important for successful germination, if you read the instructions on the labels it will usually be fine. Especially sowing on the right time is important, this will give you automatically the right amount of light (length and intensity), the right temperature, etc.

I start often indoors already with germination in small pots (or germination box) with fresh soil. Like in February for instance, then in April/May they are ready to be planted outside.

Answer 2

That is a wide range of species with somewhat different needs, though I don't recognize any of them as needing cold or warm stratification or other special treatments. Most lettuces need some light directly on the seeds, so don't bury them just press in the surface.(though some modern breeds or certain seed pre-treatments can avoid the need for light.) lettuce will germinate as low as 40f and is actually inhibited by high temperatures. All of those leaf greens would sprout well around 65f, 80f is the very upper limit, and they should do well even at 55f though it will take a few more days. The chives also sprout well between 50f and 70f.(onion crops can germinate as low as 35f but it will take more than a month)
I would sprout the remaining herbs between 70f and 80f, no more than 85f. Some seeds sprout better with some day-night temperature change of 5f to 10f. Watermelon are the only seeds that I know to prefer germinating at or above 90f

Answer 3

Soil or seedling mixes definitely impact germination a lot. If you find a good one, take note of it. Avoid seedling mixes that have lots of wood chips and uncomposted material.

Nitrates in the soil may enhance germination of weeds (and I assume other plants). Some people soak old seeds with some nitrates or other chemicals to help stimulate germination.

pH does have an impact on germination. A neutral pH should be best for most plants.

Arugula is super easy to germinate even in tough soils. Chives should be able to germinate in cooler temperatures than many things, whether or not they prefer it. Sorrel will sprout in very cool temperatures. Corrales azafrán safflower germinates in cold, cool, warm, or hot conditions, in shade or in sun, even in soil that other plants won't sprout easily in.

Some species of plants can be direct-seeded (planted directly in the ground outside) without problems, while others are better off started indoors, or such, and later transplanted.

From those on your list, you can direct seed at least arugula, spinach, dill, and lettuce, if not others. Cilantro and lettuce have a harder time sprouting in my soil than some things.

Basil is one you'd want to start indoors, as is done with tomatoes.

How quickly the soil dries seems to be another factor that influences germination, unless you water differently to compensate. Some soils dry out quickly, and this can have a negative impact on some plants. Increased organic matter and container size can prevent it from drying out as fast. You won't want super large containers for starting seeds, though. Just avoid the tiny ones you have to water more than once every two days.