Seed Rot

Warm winter days and glossy seed catalogs lure many novice gardeners into starting seeds too soon.


Okay, it’s true. Veteran gardeners are vulnerable to the same overly idealistic behavior. Most of us, however, have learned that starting seeds too early nearly always leads to damping off disease and seed rot. And it’s a waste of good seed, since both conditions are nearly always fatal. If the plant isn’t killed outright, it will always be stunted and fail to thrive.
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What causes seed rot?
Cold and wet are a recipe for disaster for most seeds. Seed rot occurs when seeds are placed in soil when temperatures are too low and moisture levels are too high. The moisture softens the tough outer seed coat, allowing fungi, such as Achlya plebsiana, Fusarium, Pythium, and Rhizoctonia to enter. These are not the beneficial mycorrhizae that help your plants find food. These fungi are out for blood. Okay, not blood, but they will suck the life out of your seeds and seedlings.


Seed rot symptoms
Planted too soon, seeds may plump up and then turn to mush. They will often develop a white, fuzzy growth. This growth is one of the aforementioned fungi. The fungi form a halo around the seed, and work their way inside. If that weren’t bad enough, within just a few days, several different algae will begin to colonize the fungal growth, turning it green. In both cases, the seed is being sapped of the strength it needs to grow.


​Seed needs

Locked inside a healthy seed, safe under a hard shell (seed coat), the embryo and a store of starches (endosperm) wait for conditions to be Just Right. Once specific levels of heat, light, air, and moisture are present, enzymes within the seed are activated. These enzymes convert the endosperm into usable sugars and the embryo can begin to germinate. If conditions are not correct enough, the young plant will be at a disadvantage that can be fatal.


How warm is warm enough?

The minimum soil temperature for many common garden plants is listed below. Soil temperature is taken two inches below the surface, where many of the roots will be found. Keep in mind, the optimum temperature for germination is often 20°F to 40°F higher:

• 35°F - lettuce, onion, parsnip, spinach
• 40°F - beets, cabbage, carrots, cauliflower, chard, parsley, peas, radish, turnips
• 50°F - corn, tomatoes
• 60°F - cucumber, eggplant, melons, peppers, pumpkin, squash

Until your last frost date has passed (It’s March 15, in my area.), the only way to safely start seeds any earlier is indoors or in a greenhouse, under grow lights, and on a seed mat that provides steady, controllable heat. [Do not use the same heating pad you use on your aching back - it is not designed for moisture and it will get too hot and can become a fire hazard.]


Preventing seed rot

While fungicides are frequently used in commercial farms to prevent seed rot, good cultural practices in the home garden can be enough to prevent this problem. Simply follow these three tips and your seeds should be fine:

• wait until soil and air temperatures are consistently high enough for the particular species
• plants seeds at the recommended depth
• keep the soil moist, but not soggy

As tempting as it may be to start earlier, waiting until conditions are suitable is one of the simplest ways to ensure a good harvest.