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Seed sowing: where did I go wrong?

Growing plants from seed is incredibly rewarding when all goes well
Image: Shutterstock

There’s nothing quite like the exciting promise contained in a handful of seeds, and nothing more disappointing than their failure to germinate. Even worse is watching your precious seedlings emerge, only to see them fail to thrive or wither and die.

Here are some of the most common ways that things go wrong, and how to avoid them:

Why didn’t my seeds germinate?

These tiny seeds require just a thin dust of soil to cover as they need light to germinate
Image: Shutterstock

There are many reasons why seeds fail to germinate, and not all of them are your fault! In order to germinate successfully, seeds require several needs to be met. These include water, oxygen, temperature and correct levels of light. Once you know the things that can go wrong, these setbacks are easy to avoid.

The seed was old:

Check the ‘sow by’ date on the packet. Seed that’s beyond this date will often still germinate but the success rate is reduced. Some seeds, such as parsnip, lose their viability rapidly so it’s worth buying a new packet each year.

It was too hot or too cold:

Always check the recommended germination temperature on the seed packet. Extremes of heat or cold may prevent seeds from germinating so it’s well worth monitoring the soil temperature with a soil thermometer. Most species can be sown successfully indoors at temperatures between 13C – 21C – easily achieved in a heated propagator or on a bright windowsill. Once germinated, you can move your seed trays to a slightly cooler position.

Outdoors: Keep an eye on the weather and avoid sowing if the soil is cold and wet, as this will cause the seed to rot. Seed packets usually advise when to sow direct outside but this will vary between warm southern gardens and cold northern locations. In the north it may be necessary to sow a month later than the seed packet suggests if the soil remains cold. Help early sowings along by using cloches to warm the soil.

The soil was too wet or too dry:

Too dry, and your seeds won’t germinate. Too wet, and they’re liable to rot. Ensure that seeds are kept evenly moist by thoroughly wetting and draining the compost before you begin. After sowing you can cover the seed tray with a sheet of glass or clear plastic to retain moisture – the compost should remain damp for several days or more.

If the soil surface begins to dry out, simply stand the seed tray in water until the surface becomes moist – but be sure to let it drain again. Remove the glass or plastic as soon as the seeds begin to germinate to prevent the seedlings from rotting.

Outdoors: Wet, poorly drained soils or dry, sandy soils can be difficult environments for seed germination. Both can be improved by adding plenty of organic matter such as well rotted manure or homemade compost. On wet soils this will improve drainage and air circulation, while on dry soils organic matter acts as a sponge, holding water in the soil for longer.

The seeds were sown at the wrong depth:

Some seeds need light to germinate, and some don’t. The amount of light that the seed receives is determined by how deeply it’s sown. Check the seed packet before you bury your seeds beneath the soil – if they need plenty of light to germinate they’ll only require a thin dusting of compost or vermiculite to get them underway.

If no instructions are provided, the size of the seed gives a good indicator of how deep to sow it. Very small seeds such as begonia and lettuce only need a light covering of sieved compost or vermiculite. Larger seeds like sunflowers and beans need to be sown several centimetres beneath the surface. As a general rule of thumb, most seeds should be planted at a depth of 3 to 4 times their own width.

The seed needed special treatment:

Did the seed packet mention pre-chilling, chipping, scarifying or soaking? Some treatments may sound a bit strange but they’re essential to help the seed germinate. You can find a full description of different techniques in our specialised sowing information article.

The seeds were eaten:

Outdoor sowings of beans, peas, sunflowers and other large seeds are often at risk from attack from the moment they’re sown. Mice and birds love to dig them up for an easy snack. Protect your seeds with cloches, chicken wire or netting to give them time to germinate safely. If you use netting, secure it carefully to avoid entangling birds.

For a quick recap on how to sow seeds correctly, read our seed sowing guide.

Why did my seedlings fail?

This gardener carefully checks the size of the roots before pricking out his seedlings
Image: Shutterstock

Transferring delicate seedlings from seed trays to individual pots provides each seedling with the space, light and nutrients it needs to develop into a strong, healthy plant. But this can be a critical time in the plant’s development and things don’t always go smoothly.

Here are some of the most common mistakes to avoid:

The seedlings were pricked out too early:

As a rule of thumb, most seedlings can be pricked out when the first true adult leaves show (i.e. the second set of leaves after the initial seed leaves or cotyledons).

But before you begin, it’s always worth checking that your seedlings have sufficient root growth to cope with the transplant process. Simply lift one or two seedlings out of the tray with a dibber and take a look. If the roots are still very tiny then postpone pricking out for a few more days. It won’t do them any harm and the extra time will help them cope better with the transplant.

The seedlings were pricked out too late:

It’s easy to sow too many seeds and then find that you don’t have time to prick them out. Delays in pricking out, especially for fast growers like tomatoes, can lead to competition for light and nutrients. If left for too long, your seedlings will start to look sickly as the nutrients in the soil are depleted. This can cause a significant check in their growth even after pricking them out.

The seedlings were damaged during pricking out:

Your delicate seedlings can be easily bruised and damaged so you should never handle them by the root or stem. Use the cotyledons as ‘handles’. Once the true leaves have formed, these seed leaves are no longer required so it doesn’t matter if they get damaged.

The seedlings just died:

Did your seedlings mysteriously keel over, or rot away at the base of the stem? These symptoms are signs of damping off, caused by a number of fungal diseases that often occur if the soil is persistently wet. To reduce the risk of damping off take the following steps:

  1. Use fresh, commercially-produced compost instead a half-used bag from last season.
  2. Always wash and dry pots and seed trays before re-using them. Disinfect them with a little diluted Jeyes Fluid.
  3. Don’t over water – let the compost dry out slightly between watering to keep fungal spread at bay.
  4. Water with clean tap water instead of using rain water.
  5. Keep seedlings well ventilated to ensure good air circulation.

The seedlings are tall and spindly:

Seedlings naturally grow towards the light, but when light levels are poor it can cause the growth to become tall and spindly. Warm temperatures will encourage leggy growth too. If you’re growing plants on your windowsill, this can be a real problem, resulting in thin spindly stems that flop over. Try to use the brightest windowsill possible (although it’s best to avoid direct strong sunlight as this may scorch your plants.)

The plants all died when they were moved outdoors:

Always check the weather before you move your plants outside. Cold temperatures, scorching heat, wind, and heavy rain can all damage or even kill your young plants. Even if the weather conditions are favourable, plants that have been grown indoors need to be hardened off before you can plant them outside. This allows them to acclimatise to the temperature, air movement and weather conditions before you plant them out. Place them outdoors in a sheltered position during the daytime and bring them back in at night. After 7 to 10 days, they should be able to cope with the big outdoors!

To properly refresh your mind and get the process clear, read our comprehensive article on pricking out and hardening off.

There’s nothing quite as satisfying as raising a plant entirely from seed. We hope we’ve given you lots of ideas to try if your seeds are failing to produce results. Good luck!

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Written by: Sue Sanderson

Plants and gardens have always been a big part of my life. I can remember helping my Dad to prick out seedlings, even before I could see over the top of the potting bench. As an adult, I trained at Writtle College where I received my degree, BSc. (Hons) Horticulture. After working in a specialist plantsman’s nursery, and later, as a consulting arboriculturalist, I joined Thompson & Morgan in 2008. Initially looking after the grounds and coordinating the plant trials, I now support the web team offering horticultural advice online.

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If you have ever experienced problems with seed germination or with pricking out and hardening your seedlings, we’ve put together all the possible reasons for these failures, and how to avoid them next year!

5 Fatal Mistakes For Germinating Seeds

It’s a few weeks before spring, and gardeners everywhere are starting baby plants from seed. Germinating seeds isn’t usually a difficult process, and for most veggies, the process is quite simple.

For complete instructions for starting seeds, get the seed starting guide.

But what do you do if your seeds don’t germinate?

When seeds don’t sprout, you should always take time to evaluate what happened. So I thought it would be helpful to talk about the most common reasons you might have seed germination problems.

Some years our germination is a little patchy, and occasionally whole rows of seedlings will not germinate. It is important to keep up with our germination rate to evaluate our technique and seed health.

For us, a minimum acceptable germination rate is when at least 80% of our seeds sprout. But ideally, 100% of our seeds come up, so anything less than 80 or even 90% germination rate, and we start looking at what went wrong.

Learn the 5 fatal mistakes for germinating seeds

When vegetable seeds are not germinating, there are a few common problems that you should look for.

1. You used old seeds

The first thing to consider is whether the seeds were viable in the first place. If your seeds have not sprouted within the appropriate number days (this will depend on your seeds), then you may want to consider using a pen or pencil to gently dig around in your soil and find the seed.

  • If you don’t find the seed, think back. Did youforget to put the seeds into the mix? Don’t laugh! It could happen!
  • If you find the seed, take a good look at it. You may see that it looks just the way it did when you put it in the soil. In this case, the cause for a low germination rate might be that it was an old seed or not properly stored.

If you have some old seeds and are unsure of whether your seeds were viable, you can always sprout a couple of them in a wet paper towel to check prior to planting.

For new seeds or seeds you saved last year:

  • When you saved seed, did you put them away without letting them dry completely? This can cause seeds to rot or mold.
  • Were they exposed to extreme temperatures during storage? For example, if you left seed packs in your car over the summer. High temperatures over 90 can kill the plant inside the seed.
  • Was the parent plant healthy? Seeds can harbor infection from the parent plant that may prevent sprouting, however, this is not usually the case.

2. You didn’t use new or sterilized containers

Disease issues can be a factor in seed germination. Think back to last year and whether you had any disease issues with your seedlings.

  • Most plastic containers can be reused for several years, but they need to be sanitized.

We clean ours by submersing them in bleach water at the beginning of the season.

If you are looking for a bleach alternative, try the environmentally friendly bleach alternatives that use hydrogen peroxide as their active ingredient.

Fungal and mold infections are the most common infection from dirty containers. If infection occurs you will notice a fuzzy growth on the top of the planting medium.

  • You may also see that a seed sprouts, but then rots at its base and falls over.

This is called damping off and is caused by a funal infection in your soil. A hydrogen peroxide or colloidal silver solution can help treat fungal disease on your tender plants.

3. Your technique is not right

  • If you started seeds in any mix that includes non-sterilized soil from the yard, your seeds may have been affected by disease organisms in the soil.

In order to use garden soil for starting seeds, you should sift it carefully to remove sticks and clumps. Then bake it on a cookie sheet in the oven at 180 degrees for 30 minutes. That should kill most weeds and pathogens.

You’re better off using a seed starting mix. Seed starting mix is usually a soiless mixture that has a finer grain and is free of clumps, sticks, and pathogens.

  • Did you plant your seeds too deep?

Planting your seeds too deep can cause problems with sprouting. You should also avoid pressing down on top of your seeds after you plant them. If the soil in your container is too compacted, the seeds cannot sprout or form healthy roots.

4. You didn’t provide the correct temperature

The temperature of your soil is of utmost importance in getting a good seed germination.

  • Temperatures that are too high or too low can cause problems germinating seeds.

Given all else is equal, even tray germination requires even temperatures. If temperatures plunge at night, or peak over 100 for a prolonged period, seeds will either remain dormant or die.

  • Did you leave the heat mat too high or too low?

Even when using seed starting heat mats, accidents happen. If you forget to put the temperature probe into the seed tray, the heat mat can overheat and cook the seeds.

Sometimes heat mats get accidentally turn off, or you forget to plug it in.

An alternative to the heat mat is to put them in a sunny south facing window or on top of the refrigerator. You can also use grow lights to provide heat above, and I have even seen people use rope lights to generate warmth.

5. You watered incorrectly

Seeds need to be moderately moist to sprout.

  • Seed germination is highly dependent on watering. Too dry and they won’t get the message to sprout, too wet and they will rot in the dirt.

Very young seedlings are even more tender. Seedlings do best in what we call the “Goldilocks zone.” You know Goldilocks. She likes her porridge not too hot and not too cold, but juuust right.

  • Tender seedling babies can’t tolerate drying out. While young, even a short dry period can mean death after the first wilt.

On the other hand, their tender roots will be the first victim of conditions being too wet. They can’t get the oxygen they need to carry about their business, and it will stunt or kill the seedling.

What other problems have you had germinating seeds?

If you’ve had troubles germinating seeds and this article didn’t answer your question, leave me a comment below. I’m happy to help you work out what’s going on.

It's a few weeks before spring, and gardeners everywhere are starting baby plants from seed. Germinating seeds isn't usually a difficult process, and for most veggies the process is quite simple. But what's a gardener to do if they're having problems germinating seeds? The first thing to check is