Five ways to increase your seed germination rates

When you start plants from seeds one of the most important things you want to achieve is a very high and fast germination rate. However if you try to do seed germination without any additional effort you will most likely reach sub-optimal results since there are some natural factors that hinder seed germination that need to be eliminated in order to achieve the best possible results. Today we are going to talk about five things you can do in order to provide the best conditions for the germination of your seeds.

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Temperature is very important. When doing seed germination one of the most critical factors is seed temperature. Some plants require cold temperatures to germinate – for example spinach’s germination rate drops to about half when you go from 15 to 25°C – while other plants require higher temperature – for coriander it’s basically the opposite. For your seedling emergence rate to be as high as possible ensure that you are giving them the temperature they ideally want, which depends on the plant species. Below you can see a table with germination temperatures for several plant species.

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Pretreat seeds with PEG-6000. Polyethylene glycol treatments can dramatically increase seed germination rates (see here). We have known this since the mid 1970’s and we have also known that the optimum treatment duration and air-drying effects change according to plant species. Applying a general PEG-6000 treatment, as a I described here a few years ago, might or might not work depending on the plant you’re trying to work with. For best results you need to search the scientific literature for the best PEG-6000 treatment or – if this information is not present – design your own experiments to figure this out.

Seed disinfection. Seeds are usually covered in microorganisms that can seriously impair seed germination rates. In order to eliminate this issue seeds need to be disinfected prior to germination with a chemical agent (most commonly either hydrogen peroxide or sodium hypochlorite solutions). For this purpose solutions in the order of 0.1-2% NaClO are generally used with different soaking times varying between different papers. You can read more about this sort of process here. Treatments are usually quick with disinfection lasting only a few minutes with subsequent plain water baths to eliminate any excess oxidant.

Introduce some good guys. In the same way that there are pathogens that can hinder seed germination there are some “good guys” that can stimulate seed germination. In particular there are trichoderma species that have been known to increase germination rates for some plant species. For example in this paper using okra (see here) there was an important increase in germination rates when using T. harzianum as a beneficial fungi. You should look for some scientific literature surrounding the species that interest you or – if that’s not available – apply a product that contains a few trichoderma species.

Using GA3 for stimulation. The final trick in your arsenal to increase germination rates is to use Gibberellic acid to stimulate your seed germination. Optimum concentration of gibberelic acid, treatment lengths and effects depend fundamentally on the plant species used but this is acknowledged to be a quite universal stimulant for seed germination rates in the general scientific literature. You can read this paper to see the effects of gibberelic acid on a wide variety of species found in western Australia (so that you can grasp how different its action can be). For particular species you can find articles like this one – for tomatoes – where different GA3 concentrations are tested to figure out the best application rate. The effect can be quite dramatic as in the image below (taken from this paper).

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In the end there are many things we can do to improve seed germination and the above is by no means an exhaustive list. For particular plant species there can be other tricks – for example things like scarification – which can lead to important improvements in germination rates as well. However the above advice is quite general and can probably help you increase germination rates for a wide variety of plant species.



Improving Seed Germination : The Science of Seed Priming

When we want to produce large amounts of plants or simply when we want to start our gardens fast and get the most out of our purchases improving seed germination becomes a large priority. One of the largest concerns of world agriculture as well as the home grower is the decrease in germination time and increase in germination percentage since both of these factors can bring great benefits. Some seeds – especially some flowers and herbs – are often quite difficult to germinate and using certain techniques to increase the rate and speed in which they sprout has been the focus of a large amount of scientific research. On today’s article I will be discussing the use of priming to decrease germination time, especially what priming is, what types are available and which ones you can use to decrease the germination time of those very difficult seeds.
To understand the concept of priming we first need a good grasp at the general concept of seed germination. A seed is a dormant embryo which carries within it the potential for a new plant’s life. The seed is alive, yet has a very slow metabolic rate due to the low mobility of substances within the embryo’s cells. This low metabolic rate allows the seed to remain alive, yet survive extremely long periods of time (some seeds can survive even hundreds of years) before actually sprouting into new plants.

Germination – which is the process in which we awaken the embryo – increases seed metabolism and toggles the massive reproduction that causes a new plant to grow. The main mechanism that triggers this process is simply liquid water. When water gets into the embryo and hydrates its cells, it speeds up metabolism and allows the process of cell division and growth to rapidly increase. However it is not always this simple to start this process since several impairments – both chemical and physical – can exist for successful germination.

Priming is simply a process done prior to conventional seed germination which allows the inhibiting mechanism to be broken and the metabolic speed increase to begin. There are several types of priming that can be done. A seed can be submerged in simple water (hydropriming), it can be soaked in a solution of a simple salt (halopriming) or it can be set in a non-ionic solution with high osmotic pressure (osmopriming). It is not entirely well established why one technique might work better than another but certainly some species tend to respond much more efficiently to one or another.
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In general, priming offers the opportunity to almost always germinate seeds at much higher speeds without detrimental effects in germination percentages. For example, a two day treatment of parsley seeds with a PEG 6000 (PolyEthyleneGlycol) solution can reduce germination times substantially, from a few weeks to just a few days. Other seeds such as coriander might also benefit from similar treatments with PEG or with treatments with NaCl solutions. In general if you are looking to test priming on some difficult seeds you own you can try three small experiments to know which one works best for your particular seed variety and germination conditions. Do one experiment in which the seeds are simply soaked in water for 24 hours, another in which seeds are placed in a 200mg/L NaCl solution and another one in which the plants are submerged in a PEG 6000 20% solution, then let the seeds air-dry after the treatments. After comparing the results of these experiments with a control with no priming you will be able to see which priming technique is better for you and most effectively increases your seed germination rates.

To sum it up priming your seeds is a very efficient technique to increase the speed of germination without sacrificing germination rates. This methods are not very useful for seeds such as lettuce or tomato – which germinate easily – but they are invaluable for plants such as parsley, coriander or carrots which are generally much harder to germinate. If you have some seeds that have been giving you a hard time or seem to take ages to germinate then setting up some priming experiments might be the best thing to do.