Understanding Seed Types

The disconnect of contemporary gardening is highlighted by the absence of seeds. In the way the modern child thinks milk comes from a carton in the fridge, the modern gardener knows plants only as ready-made advanced plants in black plastic pots purchased from the garden centre. By growing from seed we are empowered to become not just the consumers of food and garden plants but the producers.

Seeds are biological time capsules. They are complete plant packages containing embryo, food storage and protective outer coat. They allow plants to weather adverse conditions and germinate when times are good.
The oldest full seed to mature was a 2000 year old date from Herod's palace in Jerusalem. As the result of sexual reproduction, the seed carries with it possibilities of variation and evolution that do not exist when plants are grown vegetative from cuttings. This has allowed for the breeding of the myriad varieties of plant cultivars.

As home gardeners the most important part of seed biology is to know how to promote germination. In germination the seed absorbs water, its root tip emerges along with its cotyledons or seed leaves.

This is perhaps a plants most vulnerable life stage. For germination to start, three conditions need to be met. The seed must be viable, that is, it must be alive and capable of growing. It must find itself in the appropriate environmental conditions with the right degree of water, light temperature and oxygen. Finally, any dormancy needs to be broken.

Seed dormancy is a mechanism that inhibits seeds from germinating in unfavourable conditions. It pays to know the original habitat of a plant to know what conditions it may be avoiding. It can involve a tough outer shell or a chemical. Dormancy is affected by temperature, water, air and light. Seeds of winter annuals from Mediterranean climates avoid germinating in hot dry summers by requiring cooler temperatures to break dormancy, like winter lettuce, onion, celery, primula and delphinium. Famously, the dormancy of many Australian natives is broken by the heat and smoke of bushfires.
Summer plants like corn and tomato that originate in the subtropics won't germinate below 10°C. Plants like Alyssum, with fine seed need certain light levels to avoid germinating when buried to deep.

While some plants of desert origin, like nigella, amaranthus, allium and phlox are inhibited by light to encourage germination deep where soil moisture is higher. Some seeds like legumes and wattles benefit in being soaked to soften their had protective skin. This is why it so important to read your seed packet to get the full details of when and how deep to sow your seed along, with any other treatments.

Beyond basic biology gardeners need to grapple with the terminology of seed varieties. We are told to avoid GM, or hybrid seed and grow heirlooms or open pollinated varieties. Many of these terms get conflated with one another. So here is my attempt to unpack and explain these terms.