An Alameda Garden: Save Your Seedlings! 7 Ways to Prevent Damping Off

Wednesday, March 20, 2013

Save Your Seedlings! 7 Ways to Prevent Damping Off

We've all had it happen: You sow a tray of seeds, use a good potting mix, keep it watered and warm, and then rejoice to see the little seedlings emerge from the soil. They grow up and up, stretching for the sun, and then--disaster! You awake one morning to find them stricken, stems discolored, leaves wilted, perhaps an entire crop of seedlings collapsed on top of the soil. You've just encountered the dreaded "damping off" disease.

In fact, damping off is not one disease but a general term applied to the affliction of any of a number of fungal diseases, including Botrytis, Fusarium, and Phytophthora, that affect seeds and seedlings. For a look at how damping off affects seedlings--in nature as well as in greenhouse settings--check out this video:

There's no cure for damping off, so prevention is best course of action. If you want to give your seedlings the best possible odds of avoiding damping off and surviving those tender early days, here are 7 tips to follow:
  1. Start with as sterile an environment as possible. That means using a sterile potting mix; cleaning pots or seed trays with a diluted bleach solution; treating tools like trowels, soil blockers, hand seeders, and labeling stakes with disinfectants; and using seeds that have been properly stored in a cool, dry, air-tight container.
  2. Improve the drainage of the potting mix by adding perlite, vermiculite, or clean horticultural sand.
  3. Avoid overwatering and if possible, avoid watering from above. A better approach is to set the pots or trays in a tray of water long enough to moisten the soil completely. Then empty the bottom tray of excess water.
  4. Do not add fertilizers to the potting mix when you sow the seeds. Excess nitrogen can encourage growth of fungal diseases and besides, seeds can't utilize it. Seedlings will not really benefit from fertilization until after the first set of true leaves has emerged.
  5. Good air circulation is necessary so putting a fan on a low setting over the seed trays can be helpful. A light breeze on young seedlings can also strengthen the stems.
  6. Proper light from above and heat from a heating mat below will also keep moisture under control and encourage healthier seedling growth.
  7. Avoid touching seedlings unnecessarily, especially when wet, as that can spread fungal spores, if they are present. But once you seen signs of damping off, dispose of any affected plant material as well as the soil right away before it spreads further.
With these precautions your young seedlings should have an excellent chance of growing up strong and healthy.

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