:strip_icc()/101999169-1_preview-aa7b7df0279a48b3bb93fc35a8a29e2f.jpg?w=1920&resize=1920,1420&ssl=1 "7 Ways to Stop Mold from Ruining Your Homegrown Seedlings")
Key Takeaways
- Mold on seedlings is common and typically doesn’t harm the plants.
- Seedling mold is usually caused by poor airflow or overwatering the seedlings.
- Simple fixes like scraping off the mold and adding fresh seed starting mix are very effective in reducing mold.
Discovering silver or white, thread-like mold on seedlings or seed starting mix is a common issue that can occur when seeds are started indoors or in a greenhouse. While moldy seedlings may look alarming, they don’t automatically need to be thrown in the trash. This guide explains why seedlings often get moldy indoors, and simple ways to treat and prevent mold issues so your seedlings can thrive.
Why Do Seedlings Get Moldy?
Mold spores naturally exist in the environment, seed starting mixes, and on the coats of the seeds you plant. Most of the time, these spores lie dormant. But they can sprout into mold if they encounter the perfect growing environment, like a warm and humid grow room, or overly soggy seed starting mix that’s kept warm with a seedling heating mat.
Luckily, the type of mold or fungus that grows on indoor seedlings feeds on the organic matter in seed starting mix or potting soil and doesn’t directly harm seedlings or garden plants. In fact, this mold variety can actually benefit seedlings by making soil nutrients more available to seedling roots. However, the presence of seedling mold can indicate that your growing conditions are less than ideal and need to be adjusted to avoid more serious problems like damping off.
How to Fix and Prevent Moldy Seedlings
While seedling mold doesn’t normally cause major damage, it’s still wise to take action at the first sign of mold to prevent more significant problems. Whether your seedlings are displaying mold already or you just want to avoid the problem from the start, here are seven ways to treat and prevent mold on your seedlings.
1. Remove Visible Mold
If there’s mold already growing on your seedlings, use a toothpick or other small tool to gently scrape away as much of the mold from the surface of the seed starting mix as you can. Be sure to use a gentle touch, and don’t remove too much soil so the seedling roots are exposed. The goal is to get rid of as much of the visible mold as possible, but you don’t need to remove all of your seed starting mix.
2. Add Fresh Seed Starting Mix
Once you’ve scraped away some of the mold, add a light dusting of fresh seed starting mix over the top of the soil line. This fresh layer makes it harder for mold spores to regrow.
3. Use Hydrogen Peroxide or Cinnamon
To further ensure that seedling mold doesn’t regrow, spray your plants with a mixture of 1 tablespoon of 3% hydrogen peroxide blended into 1 quart of water, or sprinkle cinnamon powder across the soil line. Hydrogen peroxide and cinnamon powder both have anti-fungal properties that can keep mold from growing on your seedlings.
4. Avoid Overwatering
The main reason why seedlings develop mold in the first place is due to overwatering. So if your seedlings have started to mold, it’s a clear sign that you’re watering them too much. On the other hand, if your seedlings don’t have mold yet, you can avoid mold issues altogether by watering carefully.
Most seedlings only need to be watered lightly when the top of the soil begins to feel a little dry. However, if your seedlings have started to mold, you may need to slightly reduce watering and allow the top of the soil to dry out more between waterings. Make sure to not let your seedlings get so dry they wilt.
Switching from top-down to bottom watering can also reduce mold issues. Place seedling cells or pots in a shallow tray filled with ¼ inch of water for 30 minutes, allow the seedlings to absorb the water, and then let the seedlings drip dry before returning them to their original growing spot.
5. Improve Airflow
Whether your seedlings have mold or not, it’s important to remove humidity domes as soon as seedlings sprout. Leaving humidity domes after the seedlings germinate can increase the risk of mold and other seedling problems. You may want to add a small fan to your grow room to boost airflow and help seedlings develop sturdier and healthier stems.
6. Turn Off Heating Mats
Seedling heating mats can help plants like tomatoes germinate faster. Be sure to turn off heating mats as soon as seedlings sprout because keeping the mats on for too long can increase the risk of mold issues.
7. Thin Out Extra Seedlings
Aside from humidity domes, having too many seedlings growing in a single pot or tray or keeping seedling trays too close together can reduce airflow and encourage mold growth. To avoid this, thin out extra seedlings when the plants have sturdy stems and at least one to two sets of true leaves. Space seedling trays a few inches apart.