What’s going on under the soil?
Many wildflowers seeds are tiny and understanding what happens under the soil can be tricky! Sarah Pocock, UK Native Seed Hub Project Assistant at the Millennium Seed Bank, outlines the processes your seeds go through on their journey from sleeping seed to striving seedling, and sheds light on why some seeds spring to life faster than others...
Germination is the process of a seed growing into a young plant. The main factors that affect the success and speed of germination are water, temperature and light.
When seeds ripen they naturally dry out, holding them in a fixed state until they get a chance to germinate. Sowing seeds onto damp soil allows the seeds to soak up moisture. The uptake of water in seeds, known as imbibition, kicks off a seed’s germination journey. The size and shape of the seed affects the speed at which it can take up water. Some of the wildflower seeds you will have sown have very hard outer seed coats, which must be broken down in the soil before the seed can absorb any water and get growing.
Coming to life
As water enters, the seed swells and biological processes fire up. Germination has started but can only continue if the seed encounters specific conditions.
All seeds are sensitive to light. Some require light for germination, particularly small-seeded annuals that tend to emerge when soil disturbance brings their seeds to the surface. Temperature is also an important factor, and all seeds need to be within their preferred temperature range – not too hot, not too cold - for the germination process to carry on. Most seeds have stored food reserves, which are activated at this stage and head towards the embryo, the tiny plant-to-be at the heart of the seed. The embryo then grows inside the seed until it has enough energy to burst through the outer coat!
A fine balance of plant hormones contributes to the control of germination, and if these chemical signals aren’t at the right levels, seeds won’t be able to start sprouting and may enter a dormant phase.
Down to earth
The most obvious first sign of germination is the emergence of the embryo, known at this stage as the radicle tip. This develops into the plant’s roots and grows downwards in response to gravity. These young roots develop sensitive root hairs which seek out water and nutrients from the soil, providing the resources needed to spur on the young seedling’s development. Make sure your plot stays moist all the time at this early stage, as the germinating seed will die quickly if it does not find water.
Shoot for the stars
Following the development of the root, a shoot is sent out which will grow into the stem and leaves. This shoot heads towards the light, in the opposite direction to the root. You might see the soil hump up a little before the shoot pushes itself through the surface. Seedlings are very delicate at this stage, so it’s important to leave your wildflower patch to itself for the time being to allow the seedlings to grow stronger.
The first leaves that you’ll see are called seed leaves, or cotyledons. These leaves allow a seedling to start making its own food via photosynthesis, the production of energy using water and carbon dioxide in sunlight. This gives the seedling a power boost and helps it to grow larger and stronger each day. The amount and type of light that reaches these young leaves is key. If they don’t get enough sunlight, the stem stretches to search for more, which can weaken the seedling and make it topple over.
The next leaves that develop are known as true leaves and may look very different to the cotyledons. These leaves are a sign of what the plant will look like when it is mature, and this is probably the first time you’ll be able to start identifying your wildflowers!
Find out more about sowing and growing wildflowers at How to Grow Wildflowers!