The Science of Seedlings

Seeds are a wonder of life. The nutritious and flavourful food we enjoy every day is somehow derived from a small, seemingly insignificant capsule. There are many stages in the journey a seed takes to eventually satisfy a stomach. One of these, of course, is the transition from seed to seedling – but how does this happen? Understanding this process Seed to seedling_flickrwill help gardeners create the perfect conditions for germinating seeds.

Each seed contains the basic components of a plant, called an embryo, which include the leaves (cotyledon) and a root (hypocotyl). Seeds also contain stored nutrients and calories called the endosperm. That’s why many seeds are eaten by animals and humans alike. An embryo is activated by special enzymes that help to duplicate plant cells. Since the seed is in soil and has no leaves to generate energy from the sun, the plant cells access the energy for growth from the endosperm. In order for an embryo to be activated, the seed must be exposed to the perfect conditions. But what are these conditions?

Moisture and water is required for metabolism and enzyme activation. When seeds are exposed to water, the seed expands, which results in the breaking of the seed coat. The embryo can then grow upwards so the leaves reach sunlight, and the roots grow downwards to access more nutrients in the soil.

Temperature affects rates of cellular duplication and growth. Most seeds will germinate at around room temperature, while others can tolerate cooler temperatures such as radishes or spinach. A full spectrum fluorescent light fixture can provide some heat to ensure seeds and soil are warm enough. In some cases, you may need a heating mat depending on where your seedling are starting to grow. Remember that windows can be drafty and make significant temperature variations. The best temperature for most seeds is between 17 and 21 degrees Celsius.

Oxygen is needed for converting energy (endosperm) in the seed into cellular growth that will transform the embryo into the first roots and shoots, called the cotyledon. These first leaves, which do not photosynthesize, will eventually drop and form true leaves. Oxygen is present in pores within the soil, so if soil is waterlogged, the seed could be starved of oxygen and the germination process can be stunted or cause a seed to rot. You want to keep your seedling wet, but not soaking. A fine misting is usually enough until the seedling germinates and starts reaching for the light.

Light is required by some seeds for germination, but this is mostly limited to forest plants that will only grow if there is enough light in the canopy. Once leaves have grown from the embryo, light is immensely important for seedlings. By this point, the energy in the endosperm is depleted and the seedling must derive its energy from light. If seedlings do not get enough light, they are susceptible to fungal diseases. Window light is usually too weak and directional. A south-facing bay window can provide a decent amount of light but to ensure consistency, full spectrum fluorescent lights are recommended.

Soil is where microorganisms and plant roots interact to provide nutrients to a plant. Soil mixes have been specifically formulated to ensure that seedlings can easily access the necessary nutrients required for growth. Seed starting mixes also discourage bacteria and fungi that can present challenges to new seedlings, and ensure retention of both air and water.

Understanding the conditions that result in germination and seedling development will help you grow healthy plants both indoors and outdoors. Starting seeds indoors will help you get the most out of a growing season. Check out this chart to see a planting calendar for the Halton region showing the ideal times to sow seeds indoors and outdoors. You can also sign up for email reminders to receive planting reminders twice a month which is extremely helpful for new and experienced gardeners alike.