A few notes about seed germination.
There are few things more saddening than planting a pot or tray of seed out and after several weeks seeing that nothing has come up and started to grow. Sometimes you will get the even more annoying scenario of a flourish of weeds that seem to have come from nowhere to populate your container.
The process of saving seeds can seem complicated as there are so many different types of plants and possible environmental conditions that they can grow under – rain forests, deserts, high altitude cool mist, lowland flooding, seaside winds, riverside, swamps, and open meadows.
However there are some basic concepts that once you understand will give you some better success.
Seeds are plants way to sexually reproduce and are a simple but amazing system. They usually have all that is needed to grow included in the seed. However they also usually need a few additional things to start the process and help them out.
It’s useful to look at the where these plant originally came from to get some ideas about how to improve their growing conditions successfully.
Environmental conditions or requirements to help seed germination.
Most plants have developed in a specific location with very specific conditions that have helped them grow successfully. Some have been lucky and grow naturally in very hospitable environments with plenty of sun, water air and nutrients. However these local conditions can also sometimes be very harsh and so they have been most successful when they have adapted. An example of this is adapting to what we call seasons where levels of light, water nutrients and temperature sometimes change radically over time.
Many of our common edible food plants are fairly easy to germinate and you can get OK results by simply dropping them into a pot of generic soil, adding water and leaving them sitting in the sun outside.
But there are some that respond to certain techniques that will give you better results – and then there are some that have very specific requirements and are a pain to get started.
Most plants have seeds that respond to the changes in the local environment. Some plants have developed the ability to package their seeds up in different ways to help deal with the changes and also to make best use of them.
Here are some examples:
Squash and cucumbers package their seeds in large fruits that add a layer of jelly-like germination inhibitors around each seed. This means that to successfully germinate and grow the fruit has to break down first and then the jelly coating needs to be removed that contains the chemicals that stop them from germinating. This can happen by being eaten and go through an animals digestive tract, being washed by large amounts of rain, sit in a rotting pool of the fruit fluid that ferments, or simply dry out in the sun. All of these methods mean that after some time the chemicals are removed or deactivated and the seed by that time is usually also in a good new location away from the parent plants and able to grow with less competition.
Solanums like tomatoes, eggplants and chilis use a similar system. But they have a need to be fully dried out as well – usually with a hot dry summer period – to about 10% moisture content before germinating. You will find tomato seeds will germinate in very low numbers down at only about 5-10% if you try to plant fresh seed without the drying process – but if you dry them out and then you add water to germinate them you will often get around 90% or more germination. This imitates the rainy season coming after a hot summer.
Some swamp plants like Celery and Parsley can take a very long time to germinate because they are not fully ripened when they fall from the plant. They may look brown and dry and ready but they require up to another month or more to complete the seed ripening process after falling from the plant to become fully viable seeds.
Carrots also originally from riverside areas generally require light to germinate properly but also require constant moisture and are quite slow. So there is always a balance of keeping them moist but out in the open on the surface in the light. There is an often used trick of placing the seeds out, watering them and then covering them with a plank of wood till you see the first seeds germinate and then taking the wood away – this seems to be an OK balance that imitates the plants natural experience.
Sun – Light or dark
Plants need light for photosynthesis to grow. There are two types of ‘Phytochromes’ in plants that help photosynthesis happen – type 1 & 2 – which respond to red and far red UV light which is just at the edge between visible and UV light. (This is why UV ‘grow lamps’ often have a red glow). Plants that usually live in low light conditions need different light from those that come from out in open high light areas.
Some seeds will not germinate without light directly on them. And some will not germinate well if the light level is low and they do not get the right kind of light. This can happen when the seeds are planted too deeply or covered too densely or just shaded.
Some seeds require light to germinate. Examples: lettuce, carrots, basil
Some seeds do not like to have light directly on them. Examples: onions and the allium family in general, sunflowers, Calendula, Nasturtium.
Many seeds do not care about light levels until the leaves pop out and start to grow out of the soil. Examples: brassicas, tomato, eggplant, cucumbers, squash family
Water or moisture
Most seeds require moisture to germinate and grow. The level of moisture in the soil required can vary a lot. If the seed has a thick coating like a sunflower or squash or melon they often need a lot of moisture to germinate successfully – but usually along with the other requirements such as air movement.
Basil needs the moisture to set off a chemical reaction that produces a jelly like substance that exudes from the seed coat and helps it germinate by ‘saving’ the water. People sometimes panic when they see this and thinks its a slime, mould or fungi – buts its just a self protection system that was developed to help basil seed germinate in Sandy soils that it usually grows in. It’s the equivalent of adding water saving crystals to potting mix. The you see this is means the seed is viable and will likely germinate well.
Some seeds benefit from being ‘presoaked’ for a few hours before planting. An example of this is peas that are all shrivelled and crinkly that expand and become fully rounded again. That way you know they have enough water in them to germinate. Once that has been done you don’t need to add much extra water to the soil when you plant them and can often leave them for a few days and let the soil dry out a bit before watering again.
Moisture levels also need to be balanced wit the temperature and evaporation levels. You can often water less by using a cover to help keep moisture around the seeds if it is very hot and there are high winds for example – which will evaporate and remove moisture from the soil.
Air and oxygen
Plants need air and specifically oxygen and carbon dioxide to grow. When you plant the seeds in soil it is a good idea to make sure they have plenty of air passing across and around them by using an open and aerated type of soil. There are only a very few aquatic plants that will grow in wet and almost airless soil. High levels of moisture will also allow fungi and moulds to grow – they love it! It is always a careful balance between keeping the moisture levels high enough to help the plant grow and yet allow access to air. This means don’t plant your seeds too deeply in soil where air cannot get to them easily as they sprout.
Most edible plant seeds we grow need a temperature of around 10c up to about 27c to germinate well combined with water and air. Seeds will often germinate in small numbers at the lower end and increase in speed and number as you get higher temperatures.
There are significant groups that have requirements at either end of that range – the solanum family ( tomatoes, eggplants and chilis), squash and cucumbers etc all love higher temperatures and will germinate in larger numbers and faster when above 25c. Peas, broad beans and lettuce all love the lower end of the scale and you will get better and faster results at about 18c and below.
The germination temperature is often very different from the growing temperature for the plant.
Many long growing plants like brassicas will germinate faster and better at higher temperatures but then grow better at lower temperatures – so you can see it probably is best to germinate these in and to late summer and grow them on into winter for harvesting.
Some plants need a long time to mature and It is useful to get seeds going long before you out them into their final growing location. So it is often a good idea getting your summer seedlings going inside or under cover well (months or many weeks) before you want to plant them.
Nutrients & available chemicals
Generally most seeds have all they need to get the plant seed to grow the first 2 leaves – and can be actually germinated in any inert substances like sand, foam, cotton wool, or vermiculite. However once they get to that leaf stage you will need to give them some sort of nutrients in the form of actual soil and compost with nutrients in them. This means potting them on to a new location or adding soil and nutrients in the form of fertilisers – be they liquid or solid.
Some plants don’t need much more than this as evidenced by Hydroponic system growth where you can very successfully grow plants like tomatoes, basil, lettuce, melons, cucumbers, many brassicas and watercress just suspended in water with all the nutrients required added to the water.
Space and competition and predators
Seeds will generally not care how close they are to each other during the first stages of germinating and growth.
However as the plants start to grow and compete with each other for nutrients and water they will start to need separating and putting into suitably larger growing spaces or containers. Doing this early is a good idea before roots start to entangle with each other.
But mutliplanting with several seeds is ok for many fast growing plants too. as they will continue to grow happily with each other in many cases. You can get extra value out of this by planting several different seed types together that will simply push each other apart and can be harvested at different times. Example – try planting a beet, a radish and a lettuce seed together in one hole. Beet seeds already do this as they have 2-3 viable seeds embedded inside each seed capsule and will simply push each other apart as they grow and expand in size.
Obstructions can be an issue for seeds trying to get to the soil surface, so its good idea to try and make sure that your seed mix is fairly fine and that you either sift out or remove large bits of woods and chaff from the soil before you put the seeds in.
One good reason to not plant direct onto the ground for many vegetable seeds is the inability to control the environment very easily and therefore have a much lower number of seeds germinate and then have the issues of other plants crowd them out or have pests eat or damage them.
There are numerous ways to control seeds more easily when planted in seed pots and trays like mesh and fabric covers, glass and plastic boxes and containers etc. But these can also work for seeds planted direct in the ground as well.
We will post more specific guides about some of these germination issues but hopefully this overview will provide some things to think about when planting out your next seasons seeds.
Here’s a quick tip to keep the mice and other pests out – place a flat sheet of perspex or plastic over your seed trays till the seeds get big enough to be leafy and transplantable. It works well to keep the seeds moist, let light though and the temperature up.