All seeds need to start growing (a process called germination) by breaking through the tough outer coating that keeps their insides safe and snuggly until conditions are right.
This is called breaking seed dormancy, and how they do this can be surprising!
1. Getting eaten
Some plants, like raspberries and blackberries, need to be gobbled up and, erm, pooed out (or 'excreted' if you want the technical term) before they can start to grow. They tend to hide their seeds in tasty fruits, which animals chow down on. While the seed passes through the animal's stomach, digestive acids break the seed's coat down, leaving seeds ready to germinate post toilet break.
Handily, the newly prepared seeds also start the growth process buried in nutritious manure, which acts as the perfect growing material (or 'substrate') for seedlings.
2. Burning in forest fires
Forest fires can be destructive, but ‘pyrophile’ or heat-loving plants rely on raised temperatures and chemical signalling from the smoke and burnt plant matter to damage the seeds’ protective coat and kickstart germination.
Other plants keep their seeds sealed up in cones or fruits that are closed with resin. The direct heat from a fire melts the resin, thus setting the seeds free to begin growing.
3. Being chilly
Some seed coats break down because of very cold conditions, called cold stratification. Seeds that use this method aren’t likely to make an online order for winter woollies any time soon!
As winter conditions, like frost, soggy ground and low temperatures, wear away the coating, the baby seed (or 'embryo') is prompted to get searching for sun, water and minerals. This is why autumn sowing works so well in the UK – our damp, dicey winters give way to spring and provide perfect conditions for cold stratification to occur.
4. Soaking in water
Being submerged in water or buried in particularly soggy ground can be great for a variety of seeds that need to germinate. Their seed coats are softened, which lets water inside to wake up the seeds. Although seed coats start off waterproof, being wet for a long time can make them much more permeable (which means liquids or gases can pass through), allowing this process to happen.
5. Being scratched
Although most of us dread the day that our phone screens get dinged up, some plants take full advantage of scratches on their seed coats; this process is called mechanical scarification. Although it sounds sci-fi as anything it’s actually pretty simple.
A lot of seeds delay germination because their seed coats keep out water and air. Scraping away the seed coat over time means eventually enough water, air, and other useful things, get through to the seed embryo inside. This usually happens around the time when growing conditions are perfect, so the seed can start germination.