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Damping Off: Why Your Seedlings Are Falling Over and Dying

Help! Did your seedlings suddenly fall over and die overnight? Find out what damping off disease looks like and how to prevent this common fungal infection from happening in your garden.

It’s a sight that every seed starter dreads: a seemingly healthy seedling, perhaps even the first to sprout, suddenly slumped over the next day with a wizened stem.

You may have blamed old seeds or even lousy seed germination for a meager crop of seedlings, but more than likely, microscopic plant pathogens were at work below the surface.

Collectively, these pathogens cause a condition called damping off disease.

What causes damping off disease?

There’s never any warning when damping off might occur. The disease can take hold of a seed before it’s even sprouted, or a seedling before it’s formed its first true leaves.

Caused by several species of seed-borne and soil-borne fungi including Pythium, Rhizoctonia, Fusarium, and Phytophthora, damping off disease can move through an entire tray of seedlings in a matter of days and once they’re infected, they’re near impossible to treat.

The plants that do survive the infection are often stunted and afflicted with “wire stem” symptoms: twisty, constricted stems that result in abnormal growth and smaller yields.

Damping off disease occurs in all types of seedlings, from tomatoes and peppers to leafy greens and root vegetables. One variety is not more susceptible than another, and disease-resistant strains will not prevent it from occurring.

While damping off can strike seeds and seedlings started outdoors, it most often affects indoor seedlings due to high humidity, poor ventilation, and overcrowded seed trays.

What does damping off disease look like?

Damping off is a fungal infection that’s generally characterized by the absence (or rotting) of roots, and thin, thread-like stems where the seedlings are infected.

But, it can also wreak havoc in seeds below the soil.

In pre-emergence damping off, fungi infect the seed as it germinates.

The infection progresses swiftly and the seed decays before a stem ever emerges. This is sometimes the cause for thin and patchy stands of seedlings where unviable seeds tend to take the blame.

In post-emergence damping off, fungi infect the stem near the soil surface.

The stem takes on a discolored, water-soaked appearance from the bottom up, weakens and withers and eventually collapses, unable to support itself. It often looks like someone — or something — just pinched it off.

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How do you prevent damping off disease?

Plant pathogens exist everywhere inside and outside, but they thrive under certain conditions that are typically found in poorly ventilated greenhouses or indoor seed starting environments.

As with most seed starting problems, it’s easier to stop damping off from happening in the first place, than try to fix it if it does. Once a stem shrivels at the base, there’s nothing you can do to save that seedling.

The good news is, damping off disease is easily preventable and you don’t need any chemicals to control it. The key is to give your seeds a clean, healthy start and keep moisture in check.

Common causes of damping off disease

1. Reusing dirty containers.

You don’t have to wash your pots if you didn’t have any problems with them last season, but it’s best to discard pots that previously held diseased plants.

To ensure healthy seedlings and minimize the chances of fungi spreading, start with fresh pots and plant markers, and tools that have been properly cleaned.

2. Using infected soil or heavy garden soil to start seeds.

When starting seeds indoors, always use clean seed starting mix that was not infested with disease last season. Make sure your seed starting mix is light and fast-draining (mixing in some perlite can help with drainage).

Resist the temptation to simply dump the soil from your yard into a pot to start your seeds. Garden soil is too heavy for seed starting pots and trays, and it often brings on other problems (like dormant weed seeds sprouting and competing with your seedlings).

2. Sowing a seed too deep.

Seed packets usually have instructions for sowing seeds, and it’s important to pay attention to seeds that need light or darkness to germinate.

As a general rule of thumb, seeds should be planted as deep as their size (measured by thickness or length).

For example, a pea seed should be planted about 1/4 to 1/2 inch deep, while a pumpkin seed should be planted about 1/2 to 1 inch deep.

For tiny seeds like basil, mustard, or carrots, sow your seeds on top of the soil, then add a layer of vermiculite or very fine granite (like chick grit) to cover. The drier, grittier surface is less likely to harbor fungi that cause damping off disease.

3. Overcrowding

Seedlings need proper airflow and spacing to not only strengthen their stems (which is part of the process of hardening off) but also to promote good root development and reduce the chances of disease.

After your seeds germinate and the seedlings grow their first true leaves, remember to thin the seedlings as needed to provide good air circulation around them.

4. Overwatering

Seedlings don’t have very deep roots, so they do better with frequent but shallow watering where the roots are concentrated.

Because of this, it’s easy to water too much, especially if your indoor seed starting mix or outdoor garden soil is on the denser side. Try to keep the soil evenly moist but not waterlogged, and make sure the water drains freely out the bottom of your pots.

At the same time, don’t let the soil dry out between watering because peat-based soil mixes are very difficult to rewet once dry, leading you to water more than you have to.

5. Wet leaves

Do you constantly find moisture on the leaves after watering? It happens easily when you water with a spray bottle, squirt bottle, or watering can from overhead, even if you try to be careful.

Soil splash is a common cause of fungal disease in plants, especially with seedlings that don’t have the benefit of mulch to protect them.

To solve this problem, try watering your pots from the bottom up to avoid wetting the stems and leaves.

6. Too much humidity

Seedlings started in greenhouses with poor air circulation tend to suffer from damping off disease if humidity levels are too high.

The same goes for seedlings started under plastic humidity domes (which essentially act as mini greenhouses). These domes work well to trap heat and provide the warm environment that most seeds prefer for germination, but once they sprout, the domes should be removed.

7. Other environmental stress, like low light or cool conditions

Damping off disease is sometimes exacerbated by environmental stress such as too little light (common when germinating seeds in a window), cold temperatures, early pest damage, or excess nitrogen.

When seedlings are stressed, their immune defenses are down, leaving them susceptible to pathogens they otherwise might have been able to fight against.

Can home remedies save a seedling from damping off disease?

Since the key to treating damping off is preventing the infection in the first place, it might make sense to preempt the problem by applying chamomile tea, clove tea, or a sprinkle of cinnamon to your soil.

All of these standard treatments for damping off disease are known for their antifungal properties, but they’re 50-50 on whether or not they actually work.

Personally, I approach seed starting as a process of natural selection. Allow your seedlings to develop naturally and the strongest ones will adapt to their environment.

Should you sterilize your soil to prevent damping off disease?

Various sources advise gardeners to sterilize their soil by baking it in an oven… literally spreading it out on a sheet pan and baking at low heat to rid the medium of microorganisms.

When you start with a clean, blank slate, no nasty pathogens are threatening to claim your poor defenseless plants.

But by sterilizing your soil this way, you’re also removing the good microorganisms that plants depend on in the circle of life, rendering them even more defenseless.

Without populations of good microbes to balance the bad, you’re inadvertently lessening your seedlings’ chances of survival in the real world.

“Living soils” — those inoculated with fungi and bacteria — simulate the environment your plant will eventually move into.

Rather than starting your seeds in a sterile potting medium, use a clean potting medium (free of disease) and drench it with compost tea as your seedling grows.

The compost tea will gradually build the microbial populations in the soil and strengthen the seedlings’ immune systems, in the same way that humans need bacteria to boost our own health.

Truth is, most cases of damping off result from overwatering and low ventilation.

Neither of these problems can be solved with fungicides.

Watch for signs of excess moisture or poor airflow as you start your seeds, and you’ll have a greater chance of raising strong, healthy seedlings.

This post updated from an article that originally appeared on March 10, 2015.

Linda Ly

I’m a plant lover, passionate road-tripper, and cookbook author whose expert advice and bestselling books have been featured in TIME, Outside, HGTV, and Food & Wine. The No-Waste Vegetable Cookbook is my latest book. Garden Betty is where I write about modern homesteading, farm-to-table cooking, and outdoor adventuring — all that encompass a life well-lived outdoors. After all, the secret to a good life is. Read more »

Help! Did your seedlings suddenly fall over and die? Find out what damping off disease looks like and how to prevent this fungal infection in your garden.

Why Are My Seedlings Leggy? What Causes Leggy Seedlings And How To Prevent It

Seed starting is an exciting time for many gardeners. It seems almost magical to place a tiny seed into some soil and watch a small seedling emerge just a short time later, but sometimes things can go wrong.

We watch with excitement as the seedlings grow taller, only to realize that they have grown too tall and are now a bit floppy. This is known as leggy seedlings. If you are wondering what causes leggy seedlings, and more importantly, how to prevent leggy seedlings, keep reading.

What Causes Leggy Seedlings?

At the most basic level, leggy seedlings are caused by a lack of light. It could be that the window you are growing your seedlings in does not provide enough light or it could be that the lights you are using as grow lights aren’t close enough to the seedling. Either way, the seedlings will get leggy.

This happens due to the natural reaction of plants to light. Plants will always grow towards a light. Leggy seedlings happen for the same reason crooked houseplants happen. The plant grows towards the light and, since the light is too far away, the plant tries to accelerate its height to get close enough to the light to survive. Unfortunately, there is only a limited amount of growth a plant can do. What it gains in height, it sacrifices in the width of the stem. As a result, you get long, floppy seedlings.

Leggy seedlings are a problem for many reasons. First, seedlings that are too tall will have problems when they are moved outdoors. Because they are thin and floppy, they can’t stand up as well to natural occurrences like wind and hard rain. Second, floppy seedlings have a hard time growing up to be strong plants. Third, seedlings that are falling over can be more prone to disease and pests.

How to Prevent Leggy Seedlings

As discussed earlier, the best way to prevent leggy seedlings is to make sure the seedlings are getting enough light.

If you are growing seedlings in a window, try to grow them in a south-facing window. This will give you the best light from the sun. If a south-facing window isn’t available, you may want to consider supplementing the light the seedlings are getting from the window with a small fluorescent bulb placed within a few inches of the seedlings.

If you are growing your seedlings under lights (either a grow light or a fluorescent light), the best way to prevent leggy seedlings is to make sure that the lights are close enough to the seedlings. The lights should remain just a few inches (7-8 cm.) above the seedlings as long as you have them indoors, or your seedlings will get too tall. Many gardeners put their lights on adjustable chains or strings so that the lights can be moved upwards as the seedlings get taller.

You can also force seedlings that are too tall to grow thicker by brushing your hands over them a few times a day or placing an oscillating fan to blow gently on them for a few hours every day. This tricks the plant into thinking that it is growing in a windy environment and releases chemicals in the plant to grow thicker stems to be better able to withstand the supposed windy environment. This should not replace providing more light, but can help prevent leggy seedlings in the first place.

We watch with excitement our seedlings grow taller, only to realize that they have gotten floppy. If you are wondering what causes leggy seedlings and how to prevent them, read this article.