While it is true that the whole phenomena of seeds sprouting is rather mysterious, it doesn’t need to be a mystery to get them to sprout. The magic is all packaged to bursting in the seed and it is just waiting for the some basic signals that it is time to eject, as it were. There are some general guidelines that will make most common garden seeds sprout.
1. Seeds need a steady exposure to water. It is by absorbing water that they expand and break free. If the water dries up too much while they are still in the process of germinating, they get stuck, either still in the seed case or under the ground. This is why so many seeds sprout in the spring, when it is typically raining enough to maintain a certain level of ground saturation.
This can be mimicked when starting things in pots. I find it works best to keep the damp soil covered with plastic for at least 2 days to really help the seeds soak up water. This way, I usually get germination in 2-7 days, depending on the seeds. Outside, it takes diligent sprinkling if the rain is not occurring. Another way to facilitate it is to pre-soak some larger, harder shelled seeds before planting. I have done this with sweet peas, in particular.
It is true that while all seeds need some degree of saturation to sprout, if they will grow into a warm weather loving plant, such as corn, peppers, squash, or beans, the seeds will not want to be kept soggy wet or they will rot.
2. Seeds need soil contact. While seeds can and will sprout in something like a damp paper towel, or even soaking in a cup of water, they have to have some sort of soil for their roots to proceed with the program. The roots provide stabilization and are designed to convey most of the needed water and nutrients to the plants from the soil. Because of this design, roots do not do well exposed to light and air.
3. Seeds need to be planted to an appropriate depth. The larger the seed, the deeper it needs to be planted, and the rule of thumb of planting it to a depth twice it’s diameter is good. Part of the reason a seed needs to be planted deeper if it is bigger is because the sprout will be bigger, too. If a large sprout does not begin growing at a deep enough level, it’s roots will be too near the surface and it will be top heavy. Conversely, if a seed is planted too deeply, it can never make it to the top and obtain vital sunlight and air for the leafy portions. (click to enlarge any photo)
4. Seeds need the correct amount of light. Fortunately, this is related to their size. Any seeds that are very small either need light to germinate or don’t mind it. Seeds that are buried deeper, like the dark. If a seed packet is not clear about this, it probably is taken care of by the depth of planting. If in doubt, you can also check a good resource like The New Seed Starters Handbook.
5. Seeds need to be able to break through the top layer of soil. Again, the size of the seed often affects this. Larger seedlings can push through heavier soil than tiny ones. For this reason, when I plant seeds like carrots or lettuce, I either make sure the soil I am sprinkling thinly over them is very crumbly or I use some dry potting soil.
6. Seeds need the right temperature range to sprout. Conveniently, plants that thrive best in cooler weather have seeds that prefer cooler temperatures to sprout in. Peas and spinach are an example of this. Plants that like warm weather, want the average temperature of the soil to be closer to that in which the pending plant will do well.
Another occasional consideration with temperature, is that some seeds need to have been exposed to low enough temperatures at some point before they will sprout. This is not a necessary for most common garden seeds, but rather for things like trees, shrubs, or very unique flowers.
7. Seeds need time to sprout. It seems that the little computer inside of some seeds wants to be really sure that conditions are right, so they like the sprouting conditions to be steady for a long time before they show their pretty little green tops. Other seeds are quicker to the punch, but none of them show right up the first day, so some patient monitoring is required for all of them.
Applying these few basic principles will get most garden seed sprouting. It takes the time of planting and maintaining, but you don’t have to understand any biochemistry or computer programming. Seeds are the ultimate easy to use packaging.