It is very disappointing when you excitedly sow your new seeds, only to find that germination rates are low. You might even encounter the problem of having no seedlings appear at all. You need to work out why your seeds aren’t germinating.
Fortunately, it is often quite easy to pinpoint the cause, and there are a number of simple measures you can take to solve the problem, whatever it turns out to be.
Environmental Problems Causing Poor Seed Germination
The first thing you have to do is think about environmental problems. Environmental problems are often the most likely cause of germination problems. Different factors in the environment will be important in determining how successfully seeds will germinate.
The three key factors in germination for common crops are how much water they get, oxygen levels and temperature.
1. Too Little Water
Water is usually required for seed germination to take place. As seeds mature, they dry out. In order to germinate successfully, these mature seeds need to take in a lot of water. It is only when they have absorbed sufficient water that cellular metabolic processes and growth can take place.
When seeds absorb water, hyrolytic enzymes will begin the process of turning stored food resources into chemicals that are necessary for processes in germination.
Seeds also often require water for the coating of each seed to break down, so that the seedling can emerge.
If you have poor germination rates, this may be because you have not provided enough water for these processes to take place. If the soil in your seed trays, containers or planting areas is too dry, you should be able to see or feel this fairly easily.
Water well, taking care not to wash your seeds away or push them too deep into the growing medium, and your seeds may well still germinate in time.
2. Too Much Water
Generally speaking, the goal will be to provide enough water to moisten the seeds. But you do not want to soak them. Of course, the amount of water required will depend on the particular type of seeds you are trying to germinate.
Overwatering is one of the leading causes for poor, patchy or non-existent germination. Watering too much can cause waterlogging and compaction, which ties into the point below. An overly humid environment can also make it more likely that you will have a problem with damping off – more on which a little later in this article.
If you have watered too much, you may be able to recover things by letting the seed growing medium dry out somewhat. However, unfortunately, if the overwatering has led to one of the other problems described below, it may be too late to save them and you may need to start over.
3. Seeds Are Not Getting Enough Oxygen
A germinating seed needs oxygen for metabolism until the process of photosynthesis takes over. Before a seedling’s leaves develop, it largely derives its energy from aerobic respiration.
Oxygen needs are interlinked with water requirements. Coatings of certain seeds need to be broken down before they can absorb water and oxygen from the environment.
Both under watering and over watering could cause seeds not to get enough oxygen for germination. Under watering may have caused problems with the coating not breaking down. Over watering may have caused the soil to become waterlogged and compacted. Compactions makes it more difficult for oxygen to get through.
But another mistake may have meant that seeds did not get the oxygen they needed. You may have buried your seeds too deeply.
Check the seed packet, in gardening books or online to see what depth seeds should be planted at. Then, if you feel this may have been the mistake you made, have another go.
You may also have chosen the wrong growing medium for the seeds you are trying to grow. This too could lead to problems with seeds not getting the oxygen (or water) they need to germinate. Make sure you know what type of growing medium is required, and replace your growing medium if you made the wrong decision last time round.
4. Temperatures Are Too Low
Other common problems with seed germination revolve around temperature. Temperature will have a bearing on cellular metabolism and growth rates.
Seeds will generally germinate within a certain temperature range. They will not germinate at all outwith this temperature range, and at the extremities of the temperature range, germination rates may be significantly reduced.
Many common garden crops germinate effectively at around the average room temperature in heated homes (60-75 degrees F.). However, there is a wide range in temperatures required.
Some seeds germinate at temperatures just above freezing, some when the soil is surprisingly cool, and others only when soil has warmed significantly. A period of cold (vernalization) is required to break dormancy for some seeds. Meanwhile, others germinate only in response to an abrupt swing in temperatures (like that that marks the changing of the seasons).
Successful growing depends on understanding the role that temperature plays on the seeds we wish to grow.
Problems with the temperatures being too low are usually experienced when seeds are sown directly outdoors. You may simply have sown your seeds too early. Or the temperatures may have seen a sudden and unexpected night time dip. In a cool or cold temperate climate, late frosts can sometimes be a problem with early sowings.
To avoid this problem, you may wish to start seeds indoors before transplanting them to their final growing positions once the weather (and the soil) more reliably warms up.
If you have a short growing season, it can be important to start sowing seeds early. As well as considering starting seeds indoors, you could also consider creating a hot bed or a cold frame in which to sow your seeds, or protecting seeds and young seedlings with a greenhouse, polytunnel, row cover or cloche.
Soil will warm more quickly under one of these structures. So it could be easier to achieve the temperatures that are required for germination.
5. Temperatures Are Too High
If you are starting your seeds indoors, or in the height of summer in a warmer climate, you may have the opposite problem. Many seeds will fail to germinate above around 90-95 degrees F. If they have experienced temperatures approaching those inside your home, or in the garden, that may be the reason for the poor or non-existent germination.
If you are starting seeds indoors, check that there are no heat sources causing a problem in the vicinity of your seed growing area. Sometimes, temperature fluctuations that are too extreme may be the problem.
Are your seeds, for example, too close to a radiator, stove or oven that goes on and off? If your greenhouse or polytunnel is getting too hot, be sure to open the structure up to create adequate ventilation.
If you are trying to germinate seeds during a very hot summer, try to provide shade to bring the temperatures down. Make sure that the soil is mulched to reduce evaporation, and water well to make sure water needs are met and to create cooler soil and air temperatures.
6. Damping Off
If your seedlings germinated, but perhaps patchily, and soon after wilted and died, you may be experiencing a problem called ‘damping off’.
Damping off is a problem that can affect most seedlings. Pre-emergence damping off will mean that seedlings fail to emerge at all. Post-emergence damping off will cause seedlings to collapse some time after germination.
It is a problem seen most often when sowing early indoors or in a greenhouse. It is most damaging in the spring when light levels and temperatures are low, and humidity can often be high. This is because seeds grow most slowly at that time. However, it can occur at any time of year.
Damping off is caused by a number of different soil-borne fungi and fungus-like organisms. These include Pythium, Phytophthora, Rhizoctonia and Fusarium.
These attack the seedlings just after germination and cause them to collapse and decay. You may see a white mold around affected seedlings, which is a give away that this is the problem.
How To Reduce The Chances of Damping Off
If you are growing your seeds in commercial compost, the fungus should not be present in your growing medium. If you are growing in home-made compost, it may have been the source of the damping off organisms.
If this is a recurrent problem with your home-made compost, you can consider using steam to sterilize the mix and destroy pathogens. However, this is rarely required and most people will have no problems using their own compost.
If you are using rainwater to water your plants, the organisms may have come from there. Make sure your water butts and containers are all clean, and sealed to stop organic material from getting in. With mains water, this should not be an issue.
Make sure your trays, pots and containers are all clean before you use them. And if damping off has been a problem, do not reuse those containers. Maintain good hygiene and carefully dispose of affected material well away from your garden growing areas and compost heap.
Sow your seeds thinly to avoid overcrowding, which can make it more likely for damping off to occur again. Don’t overwater. Make sure that the seed growing area also has good ventilation and airflow, to reduce humidity.
Why Seeds Aren’t Germinating When Environmental Conditions Are Right
Sometimes, you might be convinced that the environmental conditions were perfect. Damping off was not the problem. So what went wrong? Here are a few more reasons your seeds aren’t germinating:
7. Low Germination Rates Are Normal For the Seeds You Are Attempting to Grow
It is a fact of life that some seeds naturally have a higher germination rate than others. With any seeds, it is common for a certain proportion to fail.
For some particular species, however, you may find that only half of the seeds germinate – or even fewer. This may be due to a problem. But it could also be the case that seed germination rates are usually low for the seeds you are attempting to grow.
Check seed packets and information online or in books to see whether the results are normal for the plants you are trying to grow before immediately jumping to the conclusion that something is wrong.
8. Seeds Were Stored Incorrectly
Another reason why your seeds aren’t germinating might be that they are no longer viable. Unfortunately, seeds can lose their viability if they are not stored correctly.
For example, if your seeds were stored somewhere with temperatures that were too high, this could be the problem. They may also have been exposed to high temperatures or other environmental hazards in transit to a garden centre, to a store, or to your home.
Unfortunately, if this is the case, the seeds will not germinate at all and are no longer any good. They may have been damaged enough that they can no longer mature into healthy plants.
9. The Seeds Are Simply Too Old
It is also important to realise that seeds do have a ‘use by’ date. It may simply be that the seeds you are trying to germinate are simply too old. Seeds are only viable for a certain time period, and some will lose their viability more speedily than others.
Carrots and parsnips, for example, are amongst those seeds that lose viability at a quicker pace. Of course this means that it is important to plant your seeds in time.
Aim to plant seeds from these plants, and others that lose viability quickly, within a year. Alternatively, collect or buy these seeds afresh each year.
Seeds packets often come with a ‘sow by’ date on them. This is not a hard deadline and some seeds may still germinate after the date given. But sowing seeds after this date will often lead to lower rates of germination.
If you are saving your own seed, be sure to mark containers with the date when you collected them, so you know when to use them.
10. Seeds Were Eaten Before Germination Could Occur
If no seedlings have appeared at all, there is one final potential answer to this puzzle. If you sowed seeds outside or in an open greenhouse or polytunnel, something may have eaten the seeds before they had a change to germinate!
Birds, rats, mice or voles are the likely culprits. Though it could also have been a number of other pests.
If you think that pests eating your seeds is the problem, you can increase your chances of avoiding this problem in future by sowing seeds inside your home, or on a hanging shelf in a polytunnel or greenhouse. You can also try to protect your seeds with a cloche, row cover or mesh.
In gardening, not everything always goes according to plan. But when you slowly work through the various options to find the source or sources of a problem, then seek solutions to each one in turn, you are sure to have plenty of great success stories. If at first you don’t succeed – try, try again!