‘My porridge is too hot! My porridge is too cold! My porridge is too salty! My porridge is just right!’ Just like Goldilocks and the three bears individual seed varieties have different sensitivities and environmental requirements for optimum/ best germination chances. So before you sow your seed first find out what kind of environment they need and how long they might take to germinate. I’ve put a checklist at the end so you can see what to look for.
So What does a seed need to grow?
The key requirements for seed germination that we are taught in school are the need for moisture, warmth and oxygen. These initiate the growth and development of the seed. Seeds are not dead but dormant as they are conserving energy for the optimum time to grow. Moisture enables the activation of the seed and the breaking down of the seed coat to enable the sprout to emerge. Oxygen is needed for respiration for the seed to use the energy stored there. The temperature enables the processes to take place. These are basic requirements but some seeds require additional environmental conditions before germination can take place. More on that later..
Naturally seeds have a dormancy or rest period before germination. This often goes with a seasonal weather cycle where germination is suppressed if conditions are not good for the emerging seedling and so this protects the new plant from emerging in hostile conditions - whether they are too hot or too cold or too wet or too dry. As gardeners we use methods of encouraging our seeds out of dormancy such as soaking or artificially mimicking winter months or a change of season and warmer temperature. Sometime seeds may develop secondary dormancy as a result of adverse conditions such as heat which is why storing seeds on a window ledge in full sun, a hot greenhouse or a shed in midsummer might be the death of them or if it isn’t might cause them to go more deeply dormant.
When the seed is set it has all the resources to create a new plant. For a plant species to survive it may need to be transported away from the parent plant in order to have room and resources to mature.
How the seed is transported varies from windblown dandelion seeds to raspberries eaten by birds and mammals such as badgers; each seed may have specific requirements - for example to survive the acid in a mammals gut and still be a viable seed once it has been deposited elsewhere it develops a tough seed coat, or it may be that the chemicals in the animals gut aid germination in some species.
Many seeds have an optimal or best temperature for germination. Many of the plants we grow for our gardens are non natives meaning they are not at home in our cool, temperate climate.. They are tender plants from subtropical and tropical areas that we grow as annuals and so will sulk if we try to grow them in our gardens. My brother in law sowed some french beans in March. Nothing came up as the weather was far too cold this spring. Broad beans are happy at that time of the year but French and Runner Beans are both frost tender so wouldn’t have stood a chance if they had germinated due to the late cold snap. If planted too early seeds tend to rot in the soil.
When germinating seeds requiring consistent higher temperatures be aware of what the temperature is doing at night. Even on my sunny windowsill by a radiator the night time temperatures got down to 16-17 degrees C which for a seed such as peppers needing 20 oC plus, meant they sulked, fewer seeds germinated and those that did took longer to germinate than expected.
Germinate at cool temperatures 10-17 oC e.g. Outside in spring with protection or in a cool room or garage.
Germinate at warm temperatures 18-24 oC e.g. Room temperature in many houses especially near a heat source such as a radiator.
Germinate at hot temperatures 25-32 oC e.g.Usually need a constantly warm radiator/sunny windowsill but will do better in a temperature controlled propagator.
Once germinated seedlings usually need a slightly lower temperature than that required for germination.
Optimal moisture conditions for seeds are consistently moist but not waterlogged - even for most bog plants. Too much water can reduce the space for oxygen in the soil and compact the soil structure.
Maintain moisture and humidity while seeds germinate by covering with a sheet of glass, a plastic bag or a propagator lid. These help maintaining the consistent availability of water to the germinating seedling. Once germinated the new seedling needs increased ventilation to prevent damping off caused by fungal and bacterial issues.
Is present between the particles in soil aided by humus, worms and other insects.
Specific conditions required by some plants include:
Sunshine/Light/Surface sowing or Depth/Dark sowing - to enable seeds which need light to germinate and conversely those that need dark. Many are happy in either but check.
Soaking - where seed coat needs to be softened and for some seeds that need additional moisture to activate the embryo.
Scarification - where the seed is roughened or sanded by its environment or journey through an animal which thins the seed coat to enable moisture to be taken up and the seed to emerge.
Stratification - which mimics the seasonal changes that cause germination such as cold periods or a sudden change in temperature.
Smoke or fire - which mimic the bush fires which are needed for some species in Australia and Africa and parts of America.
Which germination method should I use?
This is often a matter of personal preference, experience, seed requirements and space and the growing medium available!
A Sowing in pots and seed trays with seed compost or multipurpose compost is the most commonly used method for many seeds.
Using clean pot or tray. Fill with seed sowing compost.
Sow the seeds at the required depth.
Cover with plastic bag, glass sheet or propagator lid to retain moisture while seeds are germinating. Allow air to circulate once seeds have germinated.
B Kitchen towel (moist but not waterlogged) and plastic container or ziplock plastic bag.
Label your plastic bag/plastic container
Moisten a square of paper towel and fold seeds inside.
Place in container leaving a gap so the container is not fully closed
C Vermiculite. Can be used in Pots, seed trays or plastic bags. Moisten before sowing the seed. Vermiculite provides good aeration and moisture retention for the seedling roots and is lightweight so seeds can easily emerge. Mist daily. It is poor in nutrients so seeds in pots will need feeding once a week with a dilute plant fertiliser until ready to pot on or used mixed with a traditional seed compost.
Sprouting larger seeds in these enables the seed to grow in a moist aerated environment. Some seeds may need soaking. Seeds need rinsing in fresh water at least once a day. Once germinated transplant to pots or use as shoots.
E Outdoors in situ.
Remove any weeds and rake to a fine tilth. Using a rake or hand fork make lines where you want the seedlings to grow. Lightly sprinkle the seed in the lines and cover according to the seed requirements. Water using a fine-rosed watering can after sowing the seed. Label the area well.
Many seeds especially vegetable seeds germinate quite quickly and we can expect to see the first green shoots in 7-10 days providing the requirements for their germination are met.
Some seeds take much longer to germinate than others so don’t despair if some varieties sprout before others from the same sowing.
It’s wise to label everything and note the date of sowing and usual time of germination. This enables you to keep track of how and when you might expect to see shoots appearing. I know I don’t always manage it and think I’ll remember when I sowed something but inevitably life gets in the way!
Checklist of seed germination requirements:
- When to sow in your area?
- Where to sow (Indoors, Outdoors, Cool Greenhouse)?
- Kind of growing medium?
- Germination temperature range?
- How long will it take to germinate?
- Depth of sowing?
- Light requirements?
- Specific instructions?
- Comments, tips or tricks?