2 | Seed Germination Basics

2 Sep 2020
by Francois

If there is one thing that counts in our favour, it is that seeds actually want to grow into plants and produce flowers and seed to ensure they are reproduced. As humans we find other purposes for plants and flowers, but to a seed, their only purpose is to grow and reproduce. Each and every seed holds all the genetic material and nutrients to ensure it gets off to a good start. And then mother nature takes it from there.

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Germination requirements

Even though seeds are programmed to grow, they require the presence of three specific things to initiate the process of germination, namely light, moisture and temperature. While you might think that seeds will eventually germinate when the conditions are right for them to do so (and you are correct in thinking that), sometimes as growers we need to imitate specific conditions to force mother nature’s hand when it comes to seed germination. And when we do, we don’t want to then be in the position where our favorite seeds fail to germinate because they don’t have the right conditions, so let’s look at these germination requirements in more detail.

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Light (or darkness) – when we normally plant seeds in the ground, we bury them in the soil, right? While most seeds require darkness for best germination (in fact the presence of light even inhibits germination for some seeds), this is not true for all. Some seeds require the presence of light for optimal germination. When we work with specific flower seed varieties, it is best to know the light requirements of each. Something to keep in mind is that once seeds have germinated, all seedlings require light to grow and establish themselves. Preventing light after germination will result in their death.

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Moisture – when seeds mature and drop from the plant, their water content is very low and they enter a state of dormancy, meaning that their metabolism slows down. This is what allows them to survive in the soil (or in our case, survive during storage) until the conditions are right for them to emerge again. When we want them to germinate, we provide them with water, which they immediately start to absorb. When their internal water content reaches a specific level, they commit to the process of germination and their metabolism kicks up a few gears. At this stage if the seeds are not kept consistently moist during the process of germination, their internal water content drops again and they die. 

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Temperature – seed germination is a complex process that involves different reactions and stages. It is so precise that these stages even have minimum, optimal and maximal temperatures at which they perform. The optimal temperature range (defined as the temperature which results in the largest percentage of seeds to germinate in the shortest amount of time) is quite large – for most seeds between 15 and 30 degrees Celsius, while the maximum temperature is between 30 and 40 degrees Celsius. Above 30 the enzymes inside the seeds start to break down. However, in general, seeds are more forgiving to being outside the optimal temperature for germination than not having sufficient water. In most cases, if the temperature is not optimal, the time that it takes to germinate will just be longer.

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A note on germination efficiency – this is an indication of the number of seeds that germinate successfully (given perfect conditions) and is indicated as a percentage. It is not always indicated on commercially sold packets, but is almost always less than 100%. Germination efficiency depends on the age of a seed and is something that differs between varieties, with some varieties boasting a 99% efficiency and some even as low as 50%. However, most seed varieties have a fairly good germination percentage and fall in the 80-100% bracket. Rest assured, we ensure that all our varieties have a good germination percentage and also indicate it on our individual packets.

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DID YOU KNOW?
When it comes to germination requirements, a rule of thumb for optimal germination temperature, is that cold hardy plants prefer a lower germination temperature (13-16 degrees C), whereas heat loving plants prefer a higher germination temperature (18-23 degrees C).

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Growing medium – technically not required for the germination process, this is the next requirement on the list directly following germination. Seeds contain genetic material as well as food storage for when they germinate. Upon germination, they first send down a root into the soil. This means that when you start to see the first little leaves pop up from the soil, the seedlings already have a lot going for them inside the soil! At this stage their food storage is low or depleted, which is why the seedlings now have a functioning root system and leaves above the soil which, in essence, enables them to make their own food. While the leaves of the seedling now require light for photosynthesis, a key requirement for the optimal functioning of its root system, is a healthy growing environment. This includes the exchange of gas, the availability of nutrients and the ability to absorb these nutrients. 

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There are a number of activities occurring at root level at any one time, one of which is gas exchange. Roots exchange gases within the air spaces in soil, which requires the soil to have a relatively open structure and to also not be waterlogged (saturated with water) – the reason why soil structure is so important. Roots are also tasked with the uptake of nutrients – plants require certain nutrients in large amounts (macronutrients such as nitrogen, phosphorus, potassium, among others) as well as some nutrients in small amounts (micronutrients such as iron, zinc, copper, among others). While the availability of these nutrients in the soil / growing medium is important, this does not necessarily mean that the roots are able to take up these nutrients. This is where soil pH (among other aspects) plays a role – if the pH is too high or too low, the roots are not able to perform optimally and the plant will suffer from nutrient deficiency, even though all the nutrients are available in the soil. All of this is to drive home the importance of choosing the correct growing medium for our seedlings and plants to ensure they thrive, which is why we recommend starting your seeds in an optimal germination mix.

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The above mentioned germination requirements (light/darkness, moisture, temperature and growing medium) are of course applicable to all seeds, whether direct sown or not.

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To direct sow or not

Some seeds need to be sown directly into their growing space instead of being started in trays first. The reason for this is that some seedlings are more sensitive to root disturbance than others. Most often it is those plants that grow a single, long taproot instead of a fibrous (branched) root system. Damaging a taproot system during transplanting is much more detrimental to the seedling than damaging only a part of its fibrous root system. However, it is not impossible to successfully transplant a seedling with a taproot. Where possible it is always recommended to start seeds in trays as we have much more control over their germination and growing environment which means a better germination result and healthier seedlings. We will always indicate which varieties are recommended to be direct sown versus starting in trays. 

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As you can see, when it comes to seed germination it is crucial that we provide our seeds with the correct conditions. They have their whole life in front of them, so let’s ensure that we have everything in place and ready for them to get off to a great start! Now, let’s focus first on some practical aspects of seed germination in trays.

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Germination setup and components

Location – Your germination / growing area should receive adequate sunlight, but should also be protected from the harsh midday sun. Ideally you want to put up a shade net / plastic that can filter the direct sunlight so that your seeds / seedlings still receive adequate light, but are protected. Dappled light shining through trees or shrubs will also do.

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Cleanliness – Young seedlings are susceptible to infections; bacterial, viral, fungal. Although many of these are transmitted by insects (more on that later), as humans we are often the culprits when it comes to infecting our plants. It is important that your germination / growing area and all equipment / tools are kept clean and hygienic at all times. Keep all unrelated and dirty items like clothes or shoes out of your clean space.

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Trays – Seed starting trays are usually available at garden centres. A multitude of different tray and cell sizes exist and in general the greater the number of cells in a tray, the smaller the individual cells. The reason that different cell sizes exist is because some seedlings grow more vigorously than others and will need more growing space over the same period of time compared to slower growers. Generally seedlings are kept in trays for anything from 30 to 60 days. Flower growers most often use 128 or 200 cell trays due to the large number of plants required. Pictured below is a 48 cell (included in our seasonal boxes) and a 200 cell tray. If you are reusing old trays, ensure they are cleaned properly before you start. Once you have had algae / mold growth on them, it can easily start up again. Use a chloride  / peroxide solution to clean off any biological matter followed by a proper rinse with clean water.

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Germination mix – As mentioned above, the ideal growing medium composition is one that has a somewhat coarse and open structure. However, it should not be too coarse as it will not hold moisture well and dry out too quickly. On the other hand, if the mixture is too fine, it will stay waterlogged and your seedlings will fail to thrive. The goal is to have a consistently moist, but not wet germination environment. You can make your own germination mix using a combination of vermiculite (see below), river sand and sifted (but not too fine) compost. Mix these in equal amounts. If you are not able to make your own, there are many seed germination mixes available commercially.

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Vermiculite – An inexpensive, mineral-derived sterile element that has a high water holding capacity. This should also be available at garden centres and is often included in germination mixes to help retain moisture. We will use it specifically at surface level where seeds have been sown to ensure moisture levels stay consistent throughout the germination process.

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Water source – It would be ideal to have a water source close by so that you can connect a pipe and use a hand-held sprayer to water your trays. Choose a good-quality spray head with adjustable spraying strength.

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When you have all your components ready to start your seeds, head over to Germination Procedure for easy to follow steps to get your seeds germinated.

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