Vibrant green leaves are a sign of a healthy plant, and they also play a key role in plants' photosynthetic and respiratory processes. On top of all of that, most of us just like to take pride in our lush, thriving gardens.
Unfortunately, many gardeners are still forced to deal with those telltale white spots indicative of mold or powdery mildew on their leaves. This is especially true for those gardeners who live in climates with continuous rain, high humidity, or infrequent but heavy downpours. Luckily, there are a few things that all of us can do to help our plants resist mold and keep it off the leaves.
Fighting Mold Ahead of Time
Start from the beginning. When picking out plants for your garden, keep an eye out for mildew-resistant varieties — i.e. plants that fight fungi fairly well on their own. Popular species include adirondack crabapple, aurora dogwood, and iceberg rose.
Plants that grow close together tend to press up against each other and trap moisture between their leaves. These leaves are much more likely to fall prey to mold or mildew over time, so you'll want to thin your plants if needed to make sure that all the remaining ones are left free to grow unencumbered.
You'll also want to watch your watering technique. Whenever possible, use a long, thin-ended watering can to deliver water straight to the roots. This is because when water pools on leaves (especially when combined with humid air), mildew and mold thrive on them. Watering in the morning during the summer is often best, since it allows the water to dissipate before night, when standing water tends to cause root rot. While not technically a mold, this disease is still caused by a fungus. And given the importance of roots, it doesn't seem wise to allow fungus to take hold there either.
Make sure your mulch isn’t a breeding ground for mold, either. If you have a bed that is prone to mold, try clearing out the dead leaves and other litter that could harbor enough moisture to promote the growth of spores. What starts in the ground can easily spread to the plants growing out of it, so weeding can also help keep air circulation up and mold levels down.
Always remember that early detection can save you a lot of time and fungicide. When you do your daily watering, take the time to inspect all the leaves. If you spot some minor mold growth, you should be able to just prune out a few leaves without harming the rest of the plant. Move these leaves far from your garden area, as leaving them on the soil will only increase the mold's chances of spreading.
Plan B: Fungicides
Choosing a fungicide after a mold infection has spread too far to simply prune out? Start by consulting your local nursery or garden center. Depending on the type of mold that's common in your area and the kinds of plants you're growing, they may recommend a number of different options. They may even recommend a home remedy like baking soda. While scientific evidence suggests that many home remedies have no effect on fungus, local gardeners often claim that they’ve had substantial success with them.
If your local garden specialist recommends it, consider using an oil or a sulfur spray. While there are tons of fungicides out there, it's extremely important to consider the toxicity of each one. If the product you end up going with is toxic, you shouldn’t use it on any plants that you know will produce edible fruits and vegetables. You should also think about whether or not this fungicide could affect the soil or kill off any pollinators in the area. In some cases, fungicides won’t even be worth the risks, even if the alternative requires you to dig out a few plants in the process. However, they are still a good option for ornamental plants, which tend to receive less attention from the local wildlife.
Many gardeners who have combatted powdery mildew in the past swear by a simple mixture of milk and water. This non-toxic spray should, like any other fungicide, be sprayed early in the day to be given enough time to dry. Spraying them preventatively on mildew-prone plants every 10 days or so also seems to have a protective effect — or at least one that's pronounced enough to actually be featured in a few scientific articles!
If you're specifically dealing with tomato leaf mold, consider using a spray that contains calcium chloride. Still, the best way to kill off all kinds of mold is to deprive them of moisture.
Using these techniques, you'll be able to prevent, halt the spread of, and eradicate any mold on your plant leaves. While there's a chance that one or two plants might lose a few of their leaves in the process, the majority of your garden will be much better off if for it.