Seed Germination

‘Seed saving’ is not just one activity – it’s more a description of a whole life cycle process – the whole point is that the seeds be used to grow new plants to continue the cycle hopefully forever.

The issue of germinating seed is a point of discussion I find comes up a lot when talking to local gardeners planning a new home vegetable patch and trying to work out when and how to get their gardens started. Picking the right time and way to get seeds growing  sometimes seems a mysterious circumstance. And even more so when trying to plan out growing and harvesting to make the most of the space available and local environment.

Germinating seeds can often be a fairly straightforward process. However sometimes they require very specific conditions to spring into life. Depending on where the plants originate from there can be many different requirements for them to become active and then grow successfully.

The majority of our common vegetables tend to be easy to germinate and grow once you have grown them for a while in your local environment and worked out a regime of direct seeding and transplanting etc. but some do require a little help to get started if it’s not an ideal gardening space you have with lots of sun, wind protection ample water and a deep composted soil. And it is best to assume that most likely we all don’t have a lot of space and ideal growing conditions where we can let our crops just all self seed and regrow as they would do naturally and still produce enough to feed a family.

Plants have developed in environments that vary greatly all over the world. Most of our common edible or primary food plants originate in fairly stable climates that only have to deal with a few occasional extremes.

But they all have to deal with issues such as temperature, moisture and light variations and then the animals, insects and microbes that predate, eat and damage  them. And then there is also the issue of other plants that may just out compete them for available resources – even at the early germination stage.

Various climates and situations have produced many adaptations to help them succeed – what follows is a discussion of some that commonly affect the germination stage of some seeds we regularly grow as food. I am mainly referring to  common culinary vegetables and herbs as examples –  the sorts of plants many ‘backyard farmers’ would grow here in Australia and New Zealand.

I use a lot of words such as “often” and “usually”  and “likely” here because there are so many variations in nature that you can only really give rough guidelines from collected experience and it is important to explore and experiment yourself with your own local conditions.

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Moisture

In environments that have distinct wet and dry periods often plants will wait for a wet period to make sure the seed has the best opportunity to grow and then flower and go to seed very quickly to catch that rain or flooding and make the most of it. ie. They tend to grow very quickly and complete their full cycle from seed though to a flowering plant in a short time and will respond very quickly to the level of moisture available.

An interesting example of this is the Capsicum & Chili pepper family that gives better germination results if their seed is first dried down to about 15% moisture content and then put back into a moist environment to grow. If the seeds are left moist, as when freshly taken from the pepper fruits, they tend to have a much lower germination rate. The regions they come from often have dry hot periods and then substantial rains that push them back into growth.

The opposite situation occurs with a plant like Parsnip where the seed needs to be very fresh and almost direct from the plant to germinate well, and if it dries out tends to become non viable very quickly.

A possible response for plants in dry or arid environments is to form succulent or moisture retentive methods to survive and avoid the need to rely on large amounts of moisture to reproduce with seeds. An example of this is to reproduce very rapidly using asexual division by growing small plantlets or having the ability to root very quickly from broken pieces of leaf or stem when put in contact with water.

Another is to have a very succulent fruit or seed pod that contains the seeds and gets them off to a good start as it decays and breaks down.

Another is to encase the seed in a hard water proof surface. This means that the amount of water has to be very large to get it to soak in and germinate the seed. The seed then only germinates when there is a known large water supply to grow on.

But the most common response in plants is to just be able to take advantage of any water that comes their way very quickly. So plants from these types of environments tend to germinate very quickly and freely once in contact with any moisture and  then go through their full growth stages rapidly to seed again.

‘Bolting’ is when a plant senses a change in the environment towards being dry again and then quickly responds by  flowering and trys to make seed before moisture is limited. It can be brought on by even a very short dry period of time.

An example of this is celery which is a swamp boundary plant that reacts very quickly to a dry change and obviously senses this as a threat to itself and will  trigger flowering after even a small time without ample water available. ( Sometimes as little as a few hours)

This is generally considered less desirable in food plants where you are trying to get the most leaf material from them – e.g. lettuce or leafy Brassicas like Cabbage. You want these plants to stay in leaf growing mode for as long as possible. However this also means that seed from these plants will likely respond very quickly to moisture and will likely germinate very quickly if the seeds are kept moist.

A great deal of our common leafy salad type vegetables and herbs are in this category and will germinate quite quickly if just kept moist in virtually any growing medium.

Pre-soaking seed for a few hours before sowing can often aid with germination – especially the larger seeds such as the legumes like broadbeans, peas etc.

Light

Seeds will often respond to available light and germinate much more successfully if either exposed to or hidden from light.

This is often seen in combination with ‘Vernalising’ – which means making the plant go through an alternating cold or hot period to trigger them to flower – or – making them respond to a specific period of light and dark imitating changing seasons where the light is more or less intense along with the temperature. Changing day lengths are often triggers for fruiting and flowering.

Pumpkins and squash often show this in the way they produce male or female flowers at different times of the year and in response to temperature changes. They tend to produce more male flowers at the beginning of the growing season when it is warmer and the days are getting longer and then switch to more female flowers when the days start to get shorter and  temperatures cool down (especially at night) going into autumn.

Or you might see it because  they are often covered by mud, leaf fall or other plant matter and growth for a period of time  and then be uncovered by weather events such  as flooding or high wind or drought that displace the soil or plants around them. You often see the results of this when  a patch of seemingly empty ground is cleared and turned or dug over by humans or animals and suddenly there is a proliferation of new plants growing up simply because the seeds have been suddenly exposed to sunlight.

A lot of wind  distributed seeds fall into this category where simply being blown from their capsules and to a new patch of soil in an open space is enough to get them to start growing.

Most common garden vegetables are generally not known to have a strong preference for being covered or uncovered when sown.

Examples:

Some plants that germinate better if they are exposed to light – sitting on top of the soil are: basil, chamomile, lemon balm, marjoram and oregano, sorrel and thyme

Some plants that germinate better if they are not exposed to light – sown under the surface of the soil are:parsley, sage, chives, coriander, dill

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Temperature

Some seeds require a minimum or maximum temperature to germinate. And there will always be an optimal temperature which lies somewhere in between where you will get the best results.

Soil and not air temperature is the most important thing to measure. You can do this by using a temperature gauge with a probe pushed into the soil about several cm deep.

Using a dark coloured container or pot to germinate seedlings can help with warming up the soil they are sitting in, or sitting them on a warm heat retentive surface. Placing them next to a dense object or wall will help with keeping the temperatures more stable and allow for heat to radiate back at them overnight.

During winter or early spring when the nights are still cold a heated pad can help with getting early seedlings growing.

In most garden spaces it is unlikely you will overheat seeds in soil unless you are placing them in a very hot sunny place with long days of direct sunlight. It is more likely you will create a problem with the water evaporating and damaging them than having being cooked by the heat.

Examples:

These are approximate guides obtained from a number of sources using minimum average night time soil temperatures below which you would expect virtually no germination to occur and the same with the maximum. Optimum temperature is when the shortest amount of time for germination occurs. You can see that some seeds are biased towards cool or warm climates by how close their optimum temps are to their min or max temps.

Vegetable Min C Optimum C Max C
Lettuce 1.7 23.9 29.4
Onion 1.7 23.9 35.0
Spinach 1.7 21.1 29.4
Parsnip 1.7 18.3 29.4
Beet 4.4 29.4 29.4
Cabbage 4.4 29.4 37.8
Carrot 4.4 26.7 35.0
Cauliflower 4.4 26.7 37.8
Celery 4.4 21.1 29.4
Chard, Swiss 4.4 29.4 35.0
Parsley 4.4 23.9 32.2
Pea 4.4 23.9 29.4
Radish 4.4 29.4 35.0
Turnip 4.4 29.4 40.6
Corn 10.0 35.0 40.6
Tomato 10.0 29.4 35.0
Asparagus 10.0 23.9 35.0
Pepper 15.6 29.4 35.0
Pumpkin 15.6 32.2 37.8
Bean 15.6 26.7 35.0
Bean, Lima 15.6 29.4 29.4
Squash 15.6 35.0 37.8
Cucumber 15.6 35.0 40.6
Eggplant 15.6 29.4 35.0
Muskmelon 15.6 32.2 37.8
Okra 15.6 35.0 40.6

Examples for some herbs:

Requires a minimum temperature of above 7C (45F) to germinate: chamomile, chervil, chives, lovage, sorrel

Requires a minimum temperature of above 10C (50F) to germinate: Fennel, dill, lemon balm, oregano, parsley, thyme, purslane

Requires a minimum temperature of above 13C (55F) to germinate: borage, marjoram, sage, winter savory

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Physical and Chemical protection or moderation

Scarifiing seed – Some seeds are encased in a very hard surface to help protect them. However they often cannot actually germinate till that seed coating is broken or damaged to allow moisture, air or light in. Some times this may actually be a coating so complete that it stops oxygen and surrounding air from getting to the seed and the germination occurs simply from exposure to air when it is broken.

There are not many of the common garden vegetable seeds that need a lot of scarifying and damage to the seed to get them to germinate but some like a good soaking to get them started which some times helps break the hard casing on them. Some seeds are encouraged by using hot water to start the soaking.

Many native Australian plant seeds require quite a lot of work on them,  including fire and heat to open the seed casing or pods to release the seeds and also smoke or smoke water to promote the germination process. The various odd chemicals that result from burnt wood in bush fires reacts with the seed coatings to initiate the germination.

Germination inhibitors – Some seeds are located inside fruits that have chemicals that stop them from germinating till they are carried a great distance away from the parent plant. It takes time for the chemicals to be washed away or dissipate naturally by being washed with rain or in a stream or even by passing through an animal or insects digestive tract and being neutralised by that process.

Parsley is an example of this and requires a great deal of water to wash the seeds to remove chemicals that inhibit germination.  A long soaking and removing that water several times  before sowing them will help with germination.

 Symbiotic biota – bacteria and fungus

There are some plants that require certain types of symbiotic bacteria and fungus to survive past the first stages of germination. This ‘biota’ actually grows in combination with the plant and provides nutrients directly to the plants. A classic typical example of this type of relationship is the legume family that has special nodes that form on the roots that holds bacteria that fixes Nitrogen from the air and supplies it as food to the legume plant roots. Peas and beans are the most commonly grown examples. Orchids are another very well know group of plants that rely on this type of growing arrangement. But new studies suggest that it is a much more common arrangement in our environment that previously thought and that many thousands of unnamed and unidentified bacteria and fungus contribute directly to our soils and commonly grown plants.

Often when you buy legumes an ‘inoculant’ powder is provided with them that contains suitable known strains of biota to add to your soil. This only generally needs to be added to the soil once when you first grow the plants and then forever after those bacteria etc will theoretically be present and contribute to the growing of the plants. Often they are not required because you have suitable biota already growing in your soil. But it is also a good thing to sometimes obtain a small handful of soil to scatter on your soil when you get seeds and plants from other people that have been growing them successfully.

This type of relationship is hard to define and identifying the relevant biota almost an impossible task, so the ‘best option’ scenario is to promote good soil development with lots of varied compost in it and try not to use additions that reduce variation in your soil like fungicides and antibiotics.

Testing germination of your seeds

Test procedures – an easy common way to work out if you have viable seed is to do a viability test. This just involves placing some seeds on a moist tissue or similar medium that will hold moisture but allow air to circulate and then – either in the dark or in shade – leaving them to do their thing. You just count the days and take note of how many of them and at what stage they germinate and start to grow. Usually you do this with more than 10 seeds so you can get a good test sample.

There are huge variations in germination based on all the factors previously mentioned but there is also the basic issue of how old the seeds are as well. Some seeds viability drops off very quickly while some can stay viable if properly stored in low moisture and cool and dark for many years. This is the basis for seed banks. Generally these banks are storing the seeds in very stable conditions in controlled containers at very low temperatures, in the dark and with low moisture levels.

Seed is often sold commercially with viability shown as a percentage and with a fixed date of expiry – although seed viability will often taper off at different rates as the seeds get older depending on the species and variety.

Some useful references:

3 responses to “Seed Germination

  1. Wow I agree totally, lots of useful information, especially in regard to seeds prefering to be sown above or below the soil. It could well explain why I have experienced such haphard germination with basil seeds. Thanks !

  2. Another tip for germination – Carrots are notorious non starters because they so easily dry out during the first stages – so sow the seed on the surface of your soil and then drop or place a piece of plywood or similar flat material on top and leave them for about a week or so till they are fully germinated and starting to grow. This traps moisture near the surface and gets them off to a really good start along with suppressing many other weed seeds. Although in the same general family as Celery and Dill which prefer light the issue of moisture is more important to them. Fennel is another anomaly in that family that prefers the dark.

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