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Seed sowing: where did I go wrong?

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.

How can you prevent weed seeds from germinating in your garden?

Cover crops differ from ‘regular’ crops in that they are grown solely so the soil is covered, rather than for harvestable things. Cover crops are used by lots of folks – grain farmers, vegetable farmers, flower farmers, and they offer lots of soil benefits, as described in this blog. But they can also help control weeds! Let’s explore how.

First, let’s think about the life of a weed seed. Better yet, let’s pretend we are a weed seed trying to grow in your garden. We’ll start sitting in or on the soil. One of the biggest threats to a seed is something most people don’t normally think about: getting eaten. Mice, crickets, beetles, ants, birds (including chickens) – these things all love to eat the seeds sitting in the soil. Often the seed-eaters are themselves constantly in danger of getting eaten. A cover crop provides protection for seed-eaters. It’s harder for a hawk to see a juicy mouse running along the ground if there’s a cover crop. The mice protected by the cover crop will eat a lot more seeds.

Pretend you, the weed seed, didn’t get eaten. It’s time to think about germinating. But you, the weed seed, can only germinate if you get the right ‘cues’. Weed seeds are incredibly smart. A lot of weed seeds will only germinate when they sense ‘pure light’. Light changes as it passes through green leaves. Weeds don’t want competition, so they will wait until there are no other living plants around before they germinate. So, what if you planted a cover crop? The cover crop, alive or dead, is blocking that pure light from hitting the soil, where you and your weed seed friends live. You might never get the cue to germinate.

Another cue seeds look for is large swings in temperature. If the soil gets really warm during the day, then cools back down at night, this is a cue there isn’t anything trying to compete with it. Under a cover crop, the soil is shaded during the warm parts of the day, so the temperature swings are much less drastic. You might sit there waiting for a cue for a long time. But the longer you sit there, the higher the chance you’ll get eaten by one of the seed-eaters.

Let’s say you managed to get all the cues you needed to germinate. Congratulations, you are a weed seedling! But your fight is just beginning. The cover crop is hogging a lot of the things you need – light, water, nutrients – it’s stealing resources. And the cover crop is bigger than you, you’ll most likely just get the ‘leftovers’. The cover crop is making your life hard, so you are not going to flourish. And again, there is the threat of being eaten. Mammals love to eat tender little seedlings, and again they love to hang out under the protection of the cover crop, so your chances of survival aren’t great.

As you can see, using a cover crop can make the life of a garden weed much more difficult. In fact, many community gardens plant cover crops in plots that don’t have an owner, just to prevent weeds from taking over. To recap, cover crops can prevent weeds by:

  • Providing protection for seed-eaters
  • Preventing weed seeds from germinating
  • Competing with weeds for resources

Are you sold? Here are three ways you can start integrating cover crops into your garden.

1. Fall-planting

A simple way to get started is to plant a winter rye cover crop in the fall (October/November) as you put the garden to bed. Many gardening seed companies offer winter rye seeds. It’s a hardy plant that survives most winters if it gets to be one soda can tall before winter truly sets in. It also puts a satisfying ‘green’ in the garden during months that can feel dreary.

2. Spring-planting

If you are reading this in December, you might think you’ve missed your cover-cropping chance. You’re wrong! You can plant an early-season cover crop such as oats and hairy vetch as early as March. Good garden areas for these include places destined for crops you’ll transplant in the summer (pumpkins, eggplants, tomatoes), or pathways you want to keep from getting weedy.

3. Summer-planting

If it gets to summer and you find you have some empty space, buckwheat is an excellent summer cover crop. It grows quickly, bees love the flowers, and is easy to kill by mowing or pulling.

For all cover crops, you need to make sure the cover crop is dead before you plant your harvesting crop. Some cover crops will die if you mow them, but others need to be pulled (you can place the pulled plants back on the ground to keep it covered), crimped (imagine stomping on the plants to break their stems), or tilled. If the cover crop is still alive, it will compete with the main crop for nutrients and light, which you don’t want.

Some other common cover crops are clovers, peas, tillage radish, mustards, barley, wheat, and Sudan grass. Many gardening companies also offer seed mixes. Once you start using cover crops you might find they are just as exciting as the food-producing plants in your garden. As a rule of thumb if you see bare soil you might have an opportunity to use a cover crop, the quiet weed fighter. Happy cover cropping!

Answered by Gina Nichols, Iowa State University

Please visit our Seed Week webpage for more information.

Read the other blogs in our seed series!

About us: This blog is sponsored and written by members of the American Society of Agronomy and Crop Science Society of America. Our members are researchers and trained, certified, professionals in the areas of growing our world’s food supply while protecting our environment. We work at universities, government research facilities, and private businesses across the United States and the world.

“Why Can’t I Grow Cilantro?” Common Cilantro Growth Problems

Cilantro really grows like a weed, and often self-seeds so a cilantro patch often cultivates itself year after year, but when starting your own cilantro from seed, I’ve noticed a lot of people have had trouble with it.

This year I also had difficulty growing cilantro. I had very, very poor germination rates, maybe less than 5% of the seeds I planted (and it was a lot of seeds) actually sprouted. I have also had some issues with young cilantro plants being stunted or dying off in previous years, but with such poor germination I had never seen before, I thought I was doing something wrong.

I later found out that the reason was likely because my seeds were old, around 5 years old, and cilantro seeds (also called coriander) lose viability relatively quickly compared to other large seeds. If you’re wondering why you can’t grow cilantro, the problem isn’t with you but likely environmental factors or poor seed quality.

As I learn more about growing cilantro from seed, I may add more common problems to the list.

Cilantro Seeds Aren’t Germinating/Sprouting

Cilantro is pretty finicky when it comes to germination. In fact, reasonably fresh cilantro seeds can sometimes have germination rates lower than 50%. In my experience, they also tend to rot easily if sown into soggy soil.

There are a few reasons why your cilantro seeds aren’t germinating.

First, it could be that your seeds are too old. Cilantro seeds can last up to 2 years without a significant decline in germination, but since the germination rate is already unreliable, that means you need to sow a lot more seeds in order to get a good set of coriander sprouting.

This is also why some people have trouble germinating cilantro from coriander seeds from the grocery store. Store-bought coriander seeds can sprout, but as a dry spice, they can already be too old to sprout by the time you buy them, and if they have been dehydrated with heat, that will make them unviable.

Your seeds may have been sown in soil that is too wet. Sopping wet soil not only leads to root rot and fungal diseases (more on that later) but can also cause seeds to rot before they even have a chance to germinate. Ensure the soil, potting mix, or seed starting mix is moist but not soggy.

It’s also possible you’ve planted your coriander seeds too deep. There is only so much energy in the seed to push the sprout up high enough to breach the top of the soil. Try to plant your coriander seeds no more than 1/2 an inch deep.

Cilantro Sprouts Keep Dying

This is a common problem many gardeners face, and it doesn’t only affect cilantro. There are many potential causes of cilantro sprouts dying, from drying out to facing a surprise killing frost. But in most cases, the problem is too much water.

The culprit is usually a disease called damping off. It’s caused by different molds that infect and kill young seedlings. These molds, such as species of Fusarium, thrive in wet, cold, dark environments with little airflow, and their spores are commonly found in nature.

Once present, you can’t stop it, but you can prevent it by making sure that the potting mix or soil is well-draining and kept moist but not soggy. If you notice this is a consistent problem, you can take it a step further and sterilize your seed-starting pots with a diluted bleach solution and use fresh potting mix.

If direct sowing outdoors, sow cilantro somewhere where the soil isn’t soggy, and is getting enough sunlight to keep the soil warm to speed up germination and growth.

Once your cilantro plants start getting more true leaves and become established, they will be strong enough to ward off any threats from damping off molds.

Cilantro Leaves Are Getting Thin

If your cilantro is already growing but now you’ve noticed the leaves are getting thin, it almost always means one thing: your cilantro is getting ready to bolt.

When you see cilantro leaves getting thin, this is the natural process of your cilantro plants switching from vegetative growth to flowering, which is called bolting.

There isn’t much you can do at this point, although some gardeners harvest the thin leaves to try to prolong vegetative growth.

Fortunately, there are ways to delay bolting. Bolting is triggered by hot and dry weather. This is why cilantro/coriander is considered a cool weather plant. The easiest way to avoid bolting is to plant coriander in the middle of summer and harvest it as a fall crop, so it grows and matures over increasing cooler days.

For spring-sown cilantro, you can plant it in a partially shady area so it stays cooler during hot summer days. Some people also drape shade cloth (blocking anywhere from 30% to 50% of sunlight) over their cilantro to keep it from bolting longer.

There are also varieties of cilantro that don’t bolt as quickly, such as ‘Slow-Bolt Cilantro’. Reviews on Baker Creek seeds report that the Slow-Bolt variety can grow well into the height of summer in a partially shaded area without bolting.

Cilantro Plant Stays Small

Cilantro that has stunted growth is often the result of temperatures that are too cold (and thus slowing down growth) or root damage.

While cilantro loves cool weather, it’s a physiological fact that plants grow more slowly in colder conditions. If you think this is the reason your cilantro is still small, you can cover your plants with some garden fleece or clear plastic (even a plastic jug for small plants) to create a mini greenhouse and warm up the soil, thus increasing their growth rate. However, just be mindful not to do it on a warm day or when the sun is too bright, as your cilantro can quickly overheat.

It’s also possible that your cilantro is stunted because of root damage. This could be due to serious root damage during transplanting, or it could be due to root rot damaging significant portions of the roots. If you suspect this is the reason, I would recommend replanting more cilantro. You can still keep the original cilantro plants there in case they start growing again; and if they don’t, they will get overtaken by the new cilantro, anyway.