How to Prevent Damping-off Disease

When growing plants from seeds indoors, you may notice white, gray, or black fuzzy mold. This mold or "fuzz" causes freshly sprouted seedlings to collapse at the soil level. The conditions caused by these fungi are collectively known as "damping-off" disease, a death sentence for seedlings.
Plants suffering from damping-off may look like they were "pinched" at the soil line. The stem becomes water-soaked and thin. The first leaves that appear, known as cotyledons, turn soft and mushy and look grayish. The seedlings' leaves shrivel and turn brown. At this point, the roots are stunted or gone. There may also be a fluffy white cobweb-like growth that appears on the infected plant. Unfortunately, once seedlings are infected, they must be destroyed and the soil disposed of.
As a gardener, you play a critical role in preventing damping off and raising healthy plants. By following the steps outlined below, you have the ablity to reduce the risk of damping off disease signficatly.
What Is Damping-Off Disease?
Several soil-borne fungi, including Pythium spp., Rhizoctonia solani, and Fusarium spp., cause damping-off disease. The good news is that this disease can be mostly prevented with good hygiene and moisture control. However, once a plant has dampening-off disease, it can not be saved.
When are seedlings at risk of Damping-off Disease?
Seedlings are vulnerable to the fungi that cause damping-off disease shortly after they germinate and sprout. That is because the seedling depends on the cotyledon leaves that appear before true leaves emerge. After the plant has several sets of true leaves the risk of dampening-off is gone. With seeds that are slow-germinating, you'll need to be watchful for longer before the risk of damping-off disease decreases.
Ensuring Sucess
Cool, wet soil and stagnant air are the perfect conditions for damping off disease to take hold of your seedlings. One of the best ways to avoid the disease is to ensure your seed starter trays are kept adequately warm (but not hot). Damping-off can be discouraged with these practices:
- Avoid using garden soil when starting seeds indoors. Most garden soil has fungal spores that can lead to damping-off.
- Use seedling starter mix instead of potting soil. The seed-starter mix is a well-draining mixture of fine particles such as peat moss, perlite, and vermiculite. Another advantage is that commercial seed starter mixes are sterilized during packaging, so they should be free of living fungi.
- Seedling starter mixes containing peat moss have a natural acidity that helps prevent fungal disease. Rehydrated peat moss discs can also offer an excellent medium for starting seeds.
If you follow the tips outlined below, your soil stands a good chance of avoiding damping off disease.
Use Clean Tools
Before filling trays with seed starting mix:
- Clean and sterilize pots and tools with diluted peroxide to kill pathogens.
- Rinse with clean water after scrubbing.
Use Fresh Seed-Starting Mix
Old potting mixes can sometimes be infected with damping-off disease and should never be reused for seed starting. Instead, use fresh seed-starting mix and steer clear of regular potting mix or garden soil for indoor seeds. Standard potting mixes and garden soil don't drain as well as seed-starting mixes, and garden soil may also contain damping-off spores.
Avoid Soggy Soil
The presence of fungus is usually a sign that your potting medium is staying too wet, causing the delicate roots of your seedlings to rot and the seedlings to die. It's a balance when it comes to watering because it is also important that your seed-starting mix does not dry out completely. If the soil dries up completely, it will damage the young roots of your seedlings. I aim for soil that feels like a damp sponge, not dry and not dripping wet.
Check the containers daily to determine watering needs. If the soil feels moist, there is no need to water. Using trays or containers with drainage holes in the bottom can help prevent the soil from becoming overly moist.
Increase Airflow
Damping off thrives in cool, moist conditions with stagnant air, particularly in closed-up growing rooms with poor airflow. However, adding a small fan to the space can boost air circulation and keep seedlings healthy. Also, remember to remove humidity domes after seedlings sprout. Install a fan near your seedlings and run it for at least a few hours daily. If your seedlings grow in a covered tray, prop the top open or remove it to increase airflow. Good airflow help prohibit fungal growth and the movement of air encourages strong stems, resulting in sturdier seedlings.
Ensure Adequate Lighting
Paying close attention to the amount of light your seedlings receive is crucial. Most seedlings require 12 to 16 hours of strong, indirect light daily to grow well. Strong indirect light not only helps the water dissipate and not sit stagnantly but also ensures the health of your seedlings. Avoid direct sunlight because covered trays get too hot and may damage the seedlings.
Temperature Control
Most seedlings are unable to grow well in a cold or hot environment. Photosynthesis occurs best when the temperature stays between 77 and 82 degrees Fahrenheit. Be aware of how much heat the heating mat under your seedlings puts out. Once the seedlings have sprouted, turn down the temperature or off to avoid overheating your plants. Damping off is more likely to occur in slow-growing seeds that take a while to germinate, while fast-growing seeds tend to be more resistant.
Thin or Pot-up Seedlings
Most plant several seeds in the same cell or tray when planting seeds. If all of the seeds sprout, they will crowd one another once they start to take root. Crowded plants don't have adequate airflow, which can lead to fungus.
Thinning out your plants by pinching out a few seedlings from each pot allows you to avoid overcrowding and increase airflow. Once the seedlings sprout two sets of "true" leaves, it's time to pot-up the seedlings into larger pots.
Properly Water the Seedlings
Most mold develops as a result of overwatering. Check the soil's moisture with your finger or a soil moisture meter. Plants only need water if the soil is dry. Just be careful not to allow the soil to dry out completely. When watering, make sure the water drains and don't allow seedlings to stand in water.
Finally, consider setting up a bottom watering system. To do this, Add water to a solid-bottom tray, allow the insert with the seedlings to soak up the moisture for an hour, and then pour off the excess water. Avoiding watering the delicate stems and new leaves can help keep the soil and plants healthy.
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