5 Tricks to Prevent Damping Off in Your Seedlings This Year
Damping off is nothing short of disheartening, but with a fresh start, the next round of seedlings can thrive. Gardening expert Katherine Rowe explores how to prevent the fungal disease from the get-go when seed-starting this year.
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Damping off leads to swift decimation of entire flats of seedlings. One day, our little sprouts are emerging, and the next, they’re toppling. A host of fungal pathogens are the culprits, and a few key cultural imbalances are the accelerants.
To deter fungal issues at the offset, several tricks help set the foundation for healthy seedling development free of disease. Prevent damping off to start, and we’ll be on the way to a viable yield.
While there’s no hope for seedlings already troubled by damping off, there’s plenty of good news for the next set. A fresh start with preventative measures keeps the disease at bay, and your next round of seeding with a few cultural adjustments can be problem-free.
Epic 6-Cell Seed Starting Trays
This design gives you the convenience of having all of your seedlings in one tray. At the same time, you can easily remove a single Epic 6-Cell Tray at a time as seedlings mature, without having to prick out individual seedlings like you would with a standard cell insert tray.
What is Damping Off?
Damping off is a common fungal and mold problem for seedlings. It often results from overwatering and soggy conditions, but it can impact seedlings in well-draining situations, too. It carries over in growing supplies, splashes in water, travels on the wind, and through pests. The fungal pathogens thrive in cool, moist situations, making seed-starting setups vulnerable.
Damping off presents with brown stems at the soil level. The stem weakens and can’t support upper growth. Seedlings collapse and die back. Several pathogens like Fusarium, Pythium, and Rhizoctonia cause the condition (we see these in the garden as wilt and rot issues). The fungi spread quickly and impact all seedings in a flat.
Once damping off occurs, there’s no cure. Toss the affected seedlings and their potting media, but keep them out of the compost pile to prevent harboring and spreading the mold and fungal spores in future applications. Start fresh for a viable round of seeding.
Symptoms of Damping Off
Damping off happens quickly in the germination process and in young seedlings. Common signs of the disease include:
- Lack of germination
- Shriveling at the soil level
- Stunted growth
- Sprouting and growth, followed by browning at the stem’s base
- Quick collapse/toppling over
- Soft, mushy leaves
- Fluffy white webbing
- Visible algae or mold on the soil surface
Sterilizing Growing Containers
The first step to prevent damping off is to sterilize pots and other seed-growing supplies if you’re not directly sowing outdoors. Pots carried over between seeding seasons can harbor remnants of disease-causing pathogens, fungi, and other organisms like insects. They remain in the debris and small particles and can spread to fresh soils and seedlings.
Remove loose debris and remnants with a brush or cloth. Next is a bath in soapy water for pots, trays, and cell packs. Dish soap or detergent works well. Wash individually or place the supplies in a tub of soapy water and rinse each clean. Two tubs come in handy: one for the soapy water and one with clean water to dip in as a rinse.
Bleach or Alcohol Solutions
Two easy methods for sterilization include a bleach and water dilution or an alcohol spray or wipe. Add one part household bleach to nine parts water in a large bucket or tub. Soak the supplies for 10 to 20 minutes. Have a clean tub of water nearby to dip and rinse the soaked pots or rinse them under running water.
As an alternative disinfectant to bleach, wiping or spraying with alcohol is an easy way to sterilize seeding supplies. You can do this as you work or for smaller batches of containers and trays.
Starting with clean, debris-free containers, use 70% undiluted isopropyl alcohol (rubbing alcohol) on a cloth or in a spray bottle. Wipe the equipment with the alcohol cloth or spray all surfaces with the solution. There’s no need to rinse with water after application.
Alcohol is also useful for disinfecting pruners and other tools at any time during use. A spray, dip, or wipe with the alcohol sanitizes tools against the spread of fungal or other disease problems as you move from plant to plant when thinning, pruning, and clipping.
Start With a Fresh, Well-Draining Seed-Starting Mix
A new, sterile seed starting mix is the best foundation to prevent damping off. Don’t reuse old potting or seed-starting media for new seedlings.
Seed-starting mix differs from potting soil. Seed-specific mixes are light and fluffy, often soilless, with fine materials to reduce compaction. They’re sterile at bagging, meaning fewer introduced pathogens, and free of weed seeds. Look for a peat-free mix that relies on more renewable materials.
If you use potting soil for starting seeds, sift it to remove any chunky bits that become impediments to young roots. Bulky pieces also create air pockets that cause problems for development, as soil may not contact the roots for moisture or nutrient uptake.
Make sure there’s ample aeration from perlite or sand to create a less dense and compacted situation. A sifted potting mix is best for seed starting in soil blocking or winter sowing techniques rather than traditional indoor sowing.
Drainage Test
For seeds started indoors or out, good drainage is essential in preventing damping off and other fungal diseases. Any pots or cell trays should have drainage holes. In good cell packs, these holes are dual purpose – they allow for easy transplanting by popping the seedling out from below.
Along with draining containers, seeding media needs to be well-draining with the balance of retaining moisture. If water pools or holds on the soil surface, this indicates slow or halted flow.
High-quality seeding media is formulated for good aeration, moisture retention, and drainage. To check yours, a simple drainage test before sowing gives a good idea of runoff. Fill a few cells with the mix and water it in. Once saturated, water should flow out of the holes rather than sitting on the top or spilling over the sides.
Prevent Overwatering
Giving too much water is often the top cause of damping off. It’s easy to overwater in the spirit of nurturing our seedlings. To minimize overwatering and prevent damping off, use the soil surface as a gauge. Check the moisture level every day:
- If the surface feels dry to the touch, it’s time to water.
- When the top centimeter is dry or the surface feels crunchy or crumbly, water is in order.
- If it feels moist and sticks to your finger, hold off.
The growing environment (sunlight, temperature, humidity), container size, and potting media are variables in when to water. Observing the soil is the best indicator, rather than irrigating based on frequency or timed intervals.
Water from below to limit damp conditions on leaves. To bottom water, add water to a bottom tray for the pots or cells to absorb from the drainage hole up to the surface. Use lukewarm water in irrigating seedlings; it won’t shock roots or slow growth like cold water.
Keep Seedlings Warm
Cool temperatures foster fungal pathogens by keeping the environment moist, but moderately warm areas can help prevent damping off. Whether too cold or too hot, seedlings stressed by temperatures outside their preferred range may have weaker resistance against problems. Soils below 68°F (20°C) are susceptible to a proliferation of pathogens, as are those in hotter media above 77°F (25°C).
To prevent struggling sprouts, aim for temperatures in the ideal germination range. This is often around 70°F (21°C), signaling to the seeds that conditions are warm enough for growing. Outdoors damping off is more common in seeds sown in temperatures that are still too cool for optimal germination. Or, a snapback cool spell slows germination and growth. Wait until air and soil temps are conducive to your crop, as they vary by selection.
Indoors, place seed trays in a warm location, or opt for a heat mat if your growing space stays cool. Heat mats let us control the soil temperature close to the roots, triggering germination, strong new growth, and staving off pathogens.
Strong seedlings also need plenty of bright light for healthy development. A spot near a sunny window (but out of intense rays) works well. If your space lacks enough light, a grow light comes in handy. You can adjust intensity levels and timing, even in small-space setups.
Don’t Crowd Seeds
Cramped quarters lead to competition for space, nutrients, moisture, and light and create all-around crowded conditions with reduced airflow. Like poor drainage and excess moisture, a lack of air circulation is prime for mold and fungal development. The three are the trifecta in creating damping off situations, but fortunately, it is easy to prevent.
Minimize excessive seeding in each cell or in the garden bed using recommended spacing guidelines. If you overseed (a common practice to yield a viable crop), thin quickly as seedlings develop. Choose the most vigorous one or two seedlings to keep and clip away the others at their base. Do this early to reduce competition and increase airflow.
Thinning opens the crown for leafy development without close contact, leaving space between seedlings. Many greenhouses use fans to promote circulation and minimize stagnant air. The movement also simulates a gentle breeze to increase stem hardiness. At home, a fan can limit lingering dampness. Place a fan on a low setting five feet or more from the seedlings. Check often for dryness, as soil may dry more quickly with the added airflow than without.
