Expert Tips for Healthy Plants and Disease Prevention

With the beginning of spring right around the corner, now is the perfect time to start planning for a healthy garden. An important step you can take toward thriving flower beds, vegetables, or other plants is to consider how to stop plant disease before it starts.

There are several ways to ensure this year’s garden plants don’t get sick from last year’s pathogens. Check out these disease-prevention tips from three experts to get a head start on your healthiest garden ever.

Disinfect Seeds Before Planting

Managing disease in the vegetable garden starts with the seeds. There are bacterial and fungal pathogens that can lurk on or inside the seed, waiting to ruin your crop.

Sally Miller is a distinguished professor emerita of food, agricultural, and environmental sciences in plant pathology at the Ohio State University. According to Miller, not all seeds carry pathogens, but there are a couple of cases where you should probably disinfect the seeds before they’re planted. One is when you save your own seed and have had disease problems in the past. The other is when you buy seeds that haven’t already been commercially tested and sanitized.

Miller said hot water is one disinfection method. It kills pathogenic bacteria on the seed coat and those underneath the seed coat.

“Basically, you have a prewarming step, about 100°F for 10 minutes,” said Miller. “That’s just to kind of get the seed acclimated to the warmer temperatures. Then, you put them into 122°F for 20 to 25 minutes.”

The temperature of the water must be accurate. If it’s too hot, it will damage the seed. If it’s too cold, it won’t kill the disease. Miller said she doesn’t usually recommend this method unless there is a specific pathogen underneath the seed coat such as a bacterial canker in tomatoes and black rot on cabbage.

Most contaminants are only on top of the seed coat and are easily killed off by dunking the seeds in a Clorox mixture.

“Take 25 ounces of Clorox and 100 ounces of water so it’s a 1-to-5,” said Miller. “We use a surfactant, like dishwashing detergent – about a teaspoon. Then, you mix that up in a big bowl, and you put the seeds right in there, and you just mix it for one minute. You don’t want to overdo it because you could damage the seeds. Then, you pour it out through a sieve, and you run tap water over that for five minutes.”

After they’re rinsed, spread the seeds out to dry. Old screens make excellent drying racks.

Decontaminate Containers and Tools

Disease organisms can be moved from one place to another very easily on garden containers and tools.

Brian Hudelson is the director of the Plant Disease Diagnostics Clinic at the University of Wisconsin. He said fungi, water molds, bacteria, and nematodes can survive on a surface for years, even in adverse conditions.

According to Hudelson, the best way to make your containers disease-free is to disinfect them.

“If it’s something like clay or ceramic, I recommend washing very well with just soapy water, and then rinse them. We recommend a solution of bleach, usually roughly 10% to 20% bleach, and then soak them for roughly 20 to 30 minutes,” said Hudelson. “And then, once you’re done with that soaking, rinse them to remove any of the leftover bleach residues because those can be toxic to the plants as well.”

Disinfecting plastic containers is a bit trickier. Hudelson said there are some organisms that can’t be removed from plastic, even with bleaching. So, if the plants you were previously growing in them were healthy, you can probably treat plastic pots with bleach and they’ll be fine. However, if you had a disease problem, it’s best to just get rid of the pots.

Garden tools need disinfecting too, but Hudelson doesn’t recommend bleaching because it tends to promote rusting on metal.

“What we normally recommend for metal is 70% alcohol. If you get something like rubbing alcohol and you look at the bottle, oftentimes that’s 70% alcohol,” he said. “I would use it as a dip and treat for about 30 seconds, and then allow them to air dry. There’s some research behind the 70%; it actually works a little better for decontaminating than, say, pure alcohol.”

Zap the Soil

You can get rid of weeds, fungi, bacteria, and other nasties in the soil by heating it up. All you need is some clear plastic and the power of the sun.

When you grow the same family of vegetables in the same location year-after-year, you’re inviting a host of problems that include bacteria, insects, and troublesome soil pathogens.

Bob Polomski is an Extension horticulturist at Clemson University. He said solarization is a natural way of disinfecting the soil and creating a clean slate. It will mean giving up the growing season on that plot, but all you need is a sheet or two of clear plastic and bright sunshine.

“You would cultivate the area that is going to be solarized; you moisten it, and then you put either one sheet or two sheets of clear plastic over the top,” said Polomski. “That does a wonderful job of admitting the sun’s rays and increasing that soil temperature exceeding 120°F to 140°F. And we’re looking at a minimum of four to six weeks.”

It’s a jungle below the ground. While there are horrible pathogens down there, Polomski said we also have beneficial organisms that battle the bad ones on a daily basis. So, when you solarize the soil, you’re building up the desirables.

“There are thermophilic bacteria that actually are antagonistic to a number of these pathogens that are bent on destruction of our vegetable plants. So, it’s wonderful that we are benefitting the beneficial bacteria that are present in the soil,” he said. “We are also doing a really good job of controlling a number of weed seeds as well.”

Unfortunately, the solarization process will also kill off some of the helpful organisms, but Polomski said research shows the benefits outweigh any problems that can occur.