blog-yard-garden-news.extension.umn.edu/2020/04/troubleshooting-seedling-problems.html

Gardeners across Minnesota have been starting seedlings at home. While we hope your seedlings are healthy and vigorous, some of you are likely seeing some common problems such as seedling collapse, or tall, spindly plants. This guide is meant to help you troubleshoot issues.

Not enough light

Are your seedlings looking leggy? This is the term used for seedlings with very long, skinny stems. “Legginess” in seedlings is caused by low light, one of the most common problems when starting seeds at home.

Eventually this will result in weak stems, and the plant will struggle to support itself. If you have a sunnier window, consider moving your plants there. Otherwise you may need to include artificial lights. If you have artificial lights already, try moving them closer to the plants.

Too much water

This is another common issue with seedlings grown at home. The seedlings in the photo below are tipping over from the top; a condition known as epinasty. When your soil is water-logged it becomes hypoxic, or oxygen-deprived.

This condition can be a bit misleading, because it can look like wilt, which may cause you to want to water even more! Many people think they need to water seedlings daily, but that’s often more water than your plants need. Especially when plants are small, their root systems are not yet developed, and they will not take up very much water.

Keep your soil moist, but try to avoid soaking it. As your plants’ root systems develop, they will take up more water each day. Your potting mixture will also determine how well water drains from your system.

Seedlings suffering from limited light and too much water.
Photo: Chris Barth

Damping off

One of the most common problems affecting seedlings is damping off. This problem is caused by a number of pathogens including Rhizoctonia spp., Fusarium spp., and Pythium spp. This condition typically results in seedlings collapsing at the base of the stem, and you can often see fungus growing where the stem meets the soil.

Damping off. Photos: Michelle Grabowski, UMN Extension

Seedlings infected by damping off rarely survive. To avoid damping off, clean all of your potting media (trays, pots, any tools) thoroughly with soap and water. Sanitize if possible. Plant with clean hands, and use sterile potting media, such as a store bought potting mix.

Fungus gnat damage. Photo: Chris Barth

Insect damage

If you’re seeing small dots on your plants such as those in the photo below, check for the presence of small insects like fungus gnats. These insects typically show up when you have wet, exposed soil.

Adapting your watering routine to avoid over-saturating your soil should help to minimize insect problems. Adding a fan to promote good ventilation should also help.

Are you having any other problems with your seedlings? Feel free to post comments and ask more questions in the chat below!