TL;DR : It tells them the conditions for their germination are perfect (that spring has come for most plants and that it is time to come out of their dormancy).
Germination is the first and one of the most important steps in a plant’s life cycle. If you’ve ever grown plants from seeds you must have noticed that not all of them germinate and that they require special conditions to start growing. Most of the seeds you will grow require approximately the same conditions in order for their growth spurt to initiate. Some seeds require very special conditions in order to start their life cycles, conditions which may be hard to reproduce in a garden so there are also ways to try to replicate the elements needed artificially or at home. Plants may need various circumstances like fire (and the chemicals resulting from a forest fire) or animal interaction. Some seed need their outer shell to be dissolved by going through an animal’s digestive system (seeds ingested by birds or baobab seeds digested by elephants).
Seeds can wait for very long periods of time if not all of the right conditions are met. This is depends on the seeds, salad seeds can be kept in dry and cold conditions for only a couple of years whilst tomato seeds for example may last around 8 years sometimes (some seeds may also be frozen, there are many ways to store your seeds). The seedling will just wait inside its protective shell for spring to come.
In this first part we will explore the principal needs of a plant in order to begin germination (especially water) before later talking about plants requiring exceptional conditions to grow and the way to replicate these conditions the best way possible at home in order to accelerate this process.
Common needs
Important facts
Four main factors are required for successful germination:
- Water
- Oxygen
- Warmth
- Light
So how exactly does a seed germinate and more importantly what are seeds made of?
This is what most seeds are made of :
Seed coat
The seed coat is a tough protective outer covering or shell. Depending on the plant species it can be pretty soft (orange seeds are pretty soft, you might accidentally bite through them whilst eating your favorite fruit) to very hard (try chewing through baobab seeds). This also depends on other factors like the amount of time the seed had to mature on its parent plant. The more time seeds spend attached to the plant, the harder they get. This is why some seeds need to be picked at the beginning of the season in order to have the best germination chances. The harder a seed gets the harder it is for the embryo (or baby plant) to break through this tough shell.
Embryo
This part of the seed consists of the young root and shoot which will develop into the adult plant. It is very fragile in its first days so handle it with care!
Food store
This is a store of food (also called starch) for the new plant to use until it is large enough to make its own food, that is, when it gets its own leaves and when its root system has developed in sufficient quantity. This part is made up of one or two cotyledons, which are the food sources for baby plants. These may either stay underground or come up with the stem and the first leaves and eventually fall off when their resources are depleted (you may have seen this with beans for example).
Prerequisites
When trying to grow plants from seeds you should make sure you are not only giving them the proper conditions or in house climate to germinate but also that you are aware that seedlings are very yummy, soft and squishy to small invertebrates like slugs and that if you don’t protect them there may be a genocide overnight. Seed domes are pretty good at protecting plants all the while providing them with a warm and moist environment to grow in. You can buy a seed dome or make your own DIY miniature seed domes with plastic bottle or jugs cut in half. These will stop most pests getting in (unless they reaaaally want to). Read more about garden pests on our guide on how to regulate garden pest population.
The perfect temperature
When gardeners refer to temperature, they are talking about the temperature of the soil, not of the air. If you are planting in small plant pots, the air temperature and the temperature of your soil are usually one and the same. Sometimes that is simply not the case. For example, you can start growing seeds in hot beds (garden beds with decomposing manure warming the soil, learn more from experts : http://www.telegraph.co.uk/gardening/howtogrow/9811470/Hot-beds-beat-cold-gardens-when-you-want-to-grow-veg.html) before the air temperature starts to be acceptable for plants in spring. Most plants do not mind the cold air as much as you would think. What they really don’t like is their roots freezing in damp soil.
Hot beds are great for growing vegetables (that are adapted to your climat) early. Yet you might also want to grow other plants. Plant species and varieties have each adapted to the environment they are endemic to. This is why they will start growing in different conditions. If you like traveling around the world you have without a doubt noticed that the plants you find naturally in each country or area are sometimes totally different. You don’t find many banana trees in the North of France do you? Seems pretty logical.
Well seeds are just the same. A tropical plant is very unlikely to start growing in spring in a garden in Norway. You would not expect a tropical seed adapted to a uniformly warm-to-hot environment to thrive in cool temperatures, would you?
So if you want to start growing tropical plants, you can either get them to start growing in summer and hope they have enough time to build up resources or start them inside with the proper temperature, which sometimes requires special material (or imagination).
For example we brought back Suicide Tree or Cerebera Odollam (https://en.wikipedia.org/wiki/Cerbera_odollam) seeds from Thailand in February and they took 5 months to start growing and they only did start when the weather in France was said to be one of the worst heat-waves in years.
In a garden the soil temperature is usually a few degrees cooler (or warmer on cold winter nights) than the air temperature because the soil is cooled by evaporation from its surface. So don’t worry if your plants aren’t sprouting as soon as the weatherman announces the ideal temperature for your plant. It takes a while to warm up in spring.
Gentle bottom heat is usually best to give your seed the optimal temperature for best germination; your seed will start quicker, in a more uniform way and will be ready just in time. It might be a good idea to set your growing table on a radiator (not too hot or too dry) in front of a window at the end of the winter to get them started and ready for spring.
You can also use a waterproof seedling heat mat with a thermostat. You can find some online at a relatively cheap price if you can’t make a hot bed or if your radiators dry out the soil too quickly. This is a reliable and easily controlled way to give your little seedlings exactly the heat they require. Just be sure to use a heating mat with a thermostat because otherwise the sudden changes in temperature might damage your plants. You can set it for the temperature your seeds require and it will monitor the temperature for you, making sure you don’t accidentally bake your plants or slow their growth down by being too cold.
The ideal temperature simply signals to plants that the time is right to start a budding new life.
Some species also need a different temperature for germinating than they do for seedling growth. This might be an important thing to take into account. You really need to research what each plant needs if your want to stack the odds in your favor. We’d like to provide you with some ideas from our seed bank. We haven’t quite finished it yet unfortunately, but we should get there soon!
The right amount of moisture
Seeds need water to:
- Break open their shell: The seed coat becomes imbibed with moisture, swells up and breaks open (hopefully). Some seeds like baobabs or almonds are impervious to water and gases. This may delay or completely prevent germination. In some cases plants may need a little help from you if you wish to be successful at growing them. There are a few ways of getting through the testa (another name for the seed’s shell). Any process of breaking, scratching, or altering it through chemical, physical or thermal methods to make it permeable to water and gases is known as scarification. You may already have heard of this.
- Activate hydrolytic enzymes: Enzymes that are necessary in order to metabolise the food reserve (starch) are activated with water’s helping hand.
- Wash away abscisic acid: Abscisic acid is a plant hormone that is responsible for seed dormancy. Excess water helps to wash away this abscisic acid, allowing the plant to leave its dormancy stage.
- Help with photosynthesis: Once the food reserves in the cotyledons are all used up (you can sometimes watch this happen in beans: the cotyledons shrivel up and fall off the plant), the developing embryos produces food via photosynthesis. Water is extremely important to plants, for photosynthesis and other vital functions, if you want to learn about this, we recommend you read our post on why plants need water.
You do need moisture for seed germination, but you need it in the right quantities if you want to be successful at growing seeds. The planting medium must be kept evenly moist, but never waterlogged: too little moisture and germination will not occur; too much and your seedlings will rot.
Ready to start planting?
Be aware that the best way to start off is to have a growing medium that is already moist before adding your seeds to it. This should be done no matter the medium you are using even soilless mixes.
If you experience difficulties with gentle top watering (if you displace seeds, plants or turn over too much soil) you should definitely change your strategy and switch to watering your soil from the bottom. Try placing your container or plant pots in a tray(s) and water the tray(s) and just let the growing medium soak up what water it needs from the bottom. Do not let water sit in the tray after the plants have soaked up the water they need. The soil should be moist not drenched. Bottom watering can minimize disease, keep the soil evenly moist without overwatering, and more importantly it may prevent accidental dislodging or washing away small seeds that are just getting started, exposing them to possible death.
Personally we like growing our seeds in cleaned food containers stop with see-through lids with small holes in the for aeration. These will stop most humidity from leaving the container. Water will evaporate and condense on the walls and lid. Once the condensation merges into droplets these will just fall back into the soil. You will need to water your seedlings much less often.
While seeds need a humid atmosphere to germinate, seedlings need good air circulation to thrive. So if you try to use this method please remove the lid as soon as your seedling grow their first leaves. Just take the cover off and rely on the growing medium to supply the moisture needed (with your help), not the air.
Sunlight (or artificial lighting)
Providing your seeds with the right lighting conditions is as important as giving them the temperature and moisture they need. Most seeds need light to germinate, some require darkness, and some pretty much don’t care one way or another. Once more it’s up to you to learn what each seed’s needs are.
If light is a vital element in your seeds growth, simply plant them on top of the medium and cover it you see-through matter (like cellophane or plastic) or do not cover it at all. Some seeds grow well in wet white paper towels for example. If darkness is required, completely cover the seed with planting medium (no more than three times its diameter), unless they are too thin to be covered.
Once your seed have germinated, the seedlings will need light as much as air or water. Indeed, light is vital for plants to convert water and carbon dioxide into sugar (which plants use for food), in a process known as photosynthesis (Read about why plants need water and light). If light intensity is too low, which often happens during the short days of winter or during prolonged cloudy periods, the plants will be unhealthy, tall and spindly. This is why it is sometimes hard to start your seedlings inside in early spring. This is especially the case if you don’t have a greenhouse, a sunny window or the right material (artificial lights, …).
Find them a sunny spot (free from predators and hostile elements like strong winds) or use the right artificial lights to help you plants grow sturdy. Artificial lights.
Be sure to leave some room on windowsills for your cat (if you have one), or you’ll probably find it sleeping on your seedlings at some point. This is a common problem we have!
Air
Well, at least this one shouldn’t be too hard. There’s pretty much no way to screw this one up, so don’t worry too much about it. Just don’t try to get seeds to sprout in a closed jar.
Well you’re all set now! Just remember some plants require very special conditions in order to begin the germination process so before try on rare or expensive seeds please start with easy seeds or read about their specific germination process.
If you are really into growing from seed, you can keep a record book of when you planted, how long it took to germinate, whether you started your seed too early or too late, or whether you grew too few or too many. You should also note your plants survival rate. This way your harvest will be that much more effective the following year.
Growing plants from seeds is a constant experiment which is a lot of fun. So we recommend trying out new stuff and letting your imagination roam free.
I hope our next article will be on the best ways to get a seed to germinate!
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