Seeds are amazing little packets designed to explode with growth in the right conditions. They are tiny living, hibernating plant embryos waiting for just the right conditions. All the energy a plant needs to start it’s growing process is stored inside the seed, it just need a little water and the right temperature to unlock it.
For non-dormant seeds it’s really pretty simple. Seeds have built in germination inhibitors to insure the seed doesn’t try to sprout under difficult environmental conditions. Once the seed detects moisture and the right ambient soil temperature (78 degrees Fahrenheit for most plants) some of these inhibitors are destroyed and the seed is able to take in water. This process of taking in water is referred to as imbibition (from imbibe which means “to drink”).
As seeds take in water they expand and the internal enzymes and stored food supply hydrate and become active increasing the plant’s metabolism. Hydration also happens through osmosis at the cellular level creating a type of hydrostatic pressure called turgor pressure that forces the cells to expand. This pressure is what gives plant cells the structure they need to push through soil and against gravity as the the plant grows.
To jumpstart this germination process, gardeners have long used a process called “pre-soaking”. Soaking your seeds for 12 to 24 hours in warm water before planting will soften the seed coat, leach out any moisture dependent germination inhibitors and trigger the chemical reactions inside the seed for germination. This can decrease germination time in many common garden seeds.
The first sign of a successfully germinated seed is the expansion of the radicle out of seed and into the beginnings of a root. This immature root will reach into the growing medium in an attempt to anchor the seedling for growth and to seek out nutrients. In dicots, the radicle will continue to develope into the tap root and more root structure will form as secondary or branch roots. In monocots, there is no tap root and more roots will form in a loose bunch directly from the base of the stem.
Next in the germination process the shoot will expand and, using the same hydrostatic pressure as the radicle, push out of the seed and extend upward in its search for light. The food stored in the seed’s cotyledon only provides enough energy for germination. To manage its dwindling resources, the seedling will slow root growth and transfer energy into elongating the shoot in an attempt to emerge from the darkness and into the light where it will find a new source of energy through photosynthesis.
Once the plant emerges into an environment with a light source and the photosynthesis engines are producing energy for the plant, it goes through a dramatic transformation called photomorphogenesis. This is where the plant turns green, begins to grow leaves and it’s growth rate increases dramatically.
How to Pre-Soak Your Seeds
Pre-soaking your seeds is a pretty straight forward process and is exactly what it sounds like. There are a couple of details to pay attention to though.
To soak your seeds you really just need two things: Seeds and water (and something to put the seeds and water in).
Start by getting a small bowl or glass jar and filling it with hot (or very warm) tap water. Tap water is fine for this process. There’s no need for fancy distilled or filtered water as it will not have an adverse effect on your germination process. Some people will recommend using a liquid solution that is slightly acidic to help get through the seed coat, but it’s not really necessary.
Now place the seeds you want to soak in the bowl of water. Allow the seeds to rest in the water as it cools down, the warmth will help convince the seed it’s time to germinate. If you have any floaters, it might be a sign that those seeds are bad or they may just need a little more time. Let the seeds soak for 12 to 24 hours in a place out of direct sunlight where the water won’t get too cold. You can likely let them soak for up to 48 hours without harming the seed but any more than that and you run the risk of drowning the seed before it can germinate.
Some larger seeds with harder seed coats might need a little roughing up to help them hydrate. Breaking down the seed coat a little by scarifying with sandpaper or a serrated knife can help the seed start absorbing water faster and speed up germination.
After soaking your seeds, you’ll see that they have softened and grown in size. You might even notice the radicle extending a little. At this point plant your seeds in your growing medium as you normally would and enjoy a much shorter germination process and earlier sprouting.