Starting seeds is on top of mind for most at the beginning of the year, so this is a post of tips on getting seeds to germinate successfully. Hopefully you might find it useful.
The Basics
Let’s start with the basics! There are some non-negotiables when it comes to seed germination. We’ll have a look at these basic requirements below.
1. Water (Moisture):
Purpose: Water activates the enzymes within the seed, softens the seed coat, and facilitates the metabolic processes required for growth.
How to Provide: Keep the soil consistently moist but not waterlogged. Excess water can deprive the seed of oxygen and lead to rot.
2. Oxygen (Aeration):
Purpose: Seeds need oxygen for cellular respiration, which provides the energy required for germination.
How to Provide: Make sure the soil is loose and well-draining. Overly compacted or waterlogged soil can reduce oxygen availability.
3. Temperature:
Purpose: Different seeds have optimal temperature ranges that promote enzyme activity and growth. (We’ll look at temperatures separately later).
How to Provide: Use a soil thermometer to monitor temperatures and adjust planting times or use seed-starting mats for warmth.
4. Light or Darkness:
Purpose: Some seeds require light to trigger germination, while others germinate better in darkness. This information should be on the seed pack. Most seeds germinate in darkness.
How to Provide:
For light-requiring seeds, sprinkle them on the soil surface and press them in gently.
For dark-requiring seeds, cover them with soil according to the recommended depth on the seed packet.
5. Viable Seed:
The seeds you’re using must be alive and capable of germination. The batches of seed we are selling now have all been tested for germination quality within the last 4 months to make sure it is of good quality. Germination quality can reduce over time, you can read more about that here. We do our best to make sure the seeds we are selling are of good quality. Very occasionally, a batch might lose its germination quality before we have realised, as mother nature is constantly at work.
The Basics Conclusion
Like anything in life, getting the basics right sets you up for success and gives you the best chance. Pay most attention to these!
Fun Seed Fact!
Some seeds can remain viable for incredibly long periods, entering a state of dormancy until conditions are just right for germination. For example, a 2,000-year-old date palm seed discovered in Israel's Masada fortress was successfully germinated in 2005.
Temperatures
Soil temperature is very important. While most vegetable herb and flower seeds are not too fussy and will germinate with no problem somewhere either side of room temperature, there are some varieties worth singling out as the germination of their seeds is more affected by temperature.
Warm Season Seed Germination
In Ireland, the most common seed varieties that people seem to have trouble germinating are below, as we certainly never get the temperatures required outdoors in Spring, and the majority of the insides of our houses wouldn’t always be at these temperatures either!
| Vegetable | Temperature Range (°C) | Germination Time (days) |
| Tomatoes | 20–30 | 6–12 |
| Peppers | 22–35 | 7–21 |
| Aubergines | 24–32 | 7–12 |
| Cucumbers | 24–35 | 3–10 |
| Zucchini & Squash | 24–35 | 4–10 |
| Corn | 18–35 | 7–10 |
What to do?
For these varieties, it is recommended to get the soil the seeds are planted in to at least the minimum requirement (20 degrees for tomatoes for example). Below are some ideas to create the required conditions.
Use a Seed Heat Mat:
A seed heat mat placed under your seed trays or pots can provide consistent warmth. These mats are designed to maintain the optimal temperature for warm season seed germination, typically between 20°C and 25°C..
Create a Humidity Dome or Greenhouse Effect:
Place a clear plastic cover or dome over your seed tray or pot. This helps maintain moisture and warmth. You can also use cling film, but make sure it doesn't touch the seeds or it doesn't block the seedlings from growing when they sprout. You'll find equipment to help with this here.
Place Seeds on a Warm Surface:
Place your pots or trays on a warm surface, such as near a radiator, heating vent, or on in the hot press! Just make sure that the heat source is not too direct to avoid drying out or overheating the seeds.
They are just some ideas. If you can’t get the soil to these temperatures, some of the seeds should still germinate slightly below the required temperature, but the rate of germination will be reduced.
Cool Season Seed Germination
Not nearly as big an issue as above, but worth noting is that people sometimes have trouble germinating Lettuce, Spinach and Onion seeds in mid Summer. These varieties can germinate less when they are at above room temperature.
When germinating these in mid Summer, don’t leave them in the greenhouse, polytunnel or similar as it is too warm. Put them in the coldest area you can find.
Temperature Conclusion
While we only looked at the most common varieties that temperature is an issue, there are certainly others I didn’t mention, so it is always good to double check this to make sure you have the best chance at success.
Fun Seed Fact!
Seeds Can Sense Gravity Before They Sprout!
Seeds contain specialised cells with structures called statoliths that help them detect gravity. This allows the emerging roots to grow downward into the soil, even if the seed is positioned upside down. This phenomenon, known as gravitropism, ensures that plants establish strong roots for stability and nutrient uptake.
Other Processes That Help (SOME) Seeds To Germinate
Not all seeds will benefit from the below processes, and they would actually damage some seeds. The majority of seeds don’t need these processes, but they might be helpful to know if a variety you have ever does.
Cold Stratification
Cold stratification is required for seeds that need a period of cold temperature to overcome dormancy. This method simulates the winter conditions that some seeds need before they can germinate.
How to Do It
1. Place the seeds in a moist medium (such as sand or vermiculite) in a plastic bag or container. The medium should be damp but not soggy.
2. Store the seeds in the refrigerator (typically at temperatures between 1°C to 5°C) for a specific period, usually between 4 to 12 weeks, depending on the plant species.
3. After the cold stratification period is complete, remove the seeds and plant them in a suitable growing medium.
Some perennial flower seeds like Echinacea, Aquilegia, Comfrey etc. can benefit from this. Some of the seeds should still germinate without doing this process but this can increase the germination rate.
Pre-Soaking Seeds
Pre-soaking vegetable seeds can help some varieties to germinate more quickly and successfully. The practice of soaking seeds before planting is used to soften the seed coat, which can promote faster water absorption and trigger the germination process. This technique is particularly useful for seeds with hard or thick coats. However, it’s not necessary for all vegetable seeds.
How To Do It
1. Place the seeds in a container with room-temperature water.
2. Soak the seeds for a period of time, typically 6 to 24 hours. It’s important not to soak them for too long, as this can lead to rotting or the seeds starting to sprout prematurely.
3. After soaking, drain the seeds and plant them immediately.
Big seeds with hard shells can benefit from this e.g. Peas, Beans, Corn, Cucumber, Squash etc.. However, the seeds should germinate very successfully without doing this process.
Nick The Seed Coat
Nicking the seed coat refers to making a small cut or scratch in the hard outer shell (seed coat) of a seed to help water penetrate it and trigger the germination process. Some seeds have thick, tough coatings that can prevent moisture from entering the seed, which slows down or even prevents germination. By nicking the seed coat, you break through this barrier, allowing the seed to absorb water more quickly and begin the germination process.
How To Do It
1. Use a Sharp Tool: You can use a sharp knife, a small file, or even a nail clipper to make a small, shallow cut or scratch on the seed coat. Be careful not to cut too deep, as this could damage the seed inside.
2. Gently Scratch or Cut: You only need to nick the seed coat, not cut it all the way through. A small scratch on the surface is sufficient.
3. Soak the Seed: After nicking, soak the seeds in water for 6-12 hours to allow the seed to absorb moisture and begin germination.
Again this isn’t a very necessary step, and it shouldn’t be done to most varieties, but it really helps with some seeds. It is a particularly good method to use to help Nasturtium seeds to germinate.
Other Processes That Help (SOME) Seeds To Germinate Conclusion
These methods can definitely help germination, but most people will likely go through their seed growing lives without ever doing them and still get satisfactory results.
Last Fun Seed Fact!
Some tree seeds have evolved to require fire as a means of breaking their dormancy, a process known as pyrogenic germination. These seeds have adapted to the natural fire cycles in their environments, where the intense heat from a fire can trigger the seeds to sprout. Fire can break down the hard seed coat, remove chemical inhibitors, and stimulate germination after a fire clears the landscape.
Overall Conclusion
Hopefully this didn’t make seed starting sound hard and complicated. The vast majority of seeds will germinate really easily if the basics are followed. Hopefully you might have found this useful and perhaps it might help your growing success rate this year.