Too much of a good thing: Excess rain causing garden problems

This time of year, most people run their vegetable garden on autopilot. Everything has been planted and the harvests may start to slowly trickle in.

While the work in the garden aside from harvesting may not be as intense as preparing and planting the beds, there’s still plenty that can be done. There are some things that you want to be doing and watching for so that you can maintain your garden. After all, you want to make sure you get a good return on your investment.

For the last few years, June and early July have presented a unique set of challenges to gardeners due to an overabundance of rain. While some rain is good to keep the garden watered, heavy rains almost every day can lead to some serious garden issues.

The first thing you should be on the lookout for is disease. With all of the rain we have had over the last several weeks, conditions are ripe for the spread of diseases, especially fungal and bacterial diseases. The rain will splash the disease up from debris in the garden or from plant to plant, and is also necessary for the fungus to begin growing on the plant.

Frequent rain and high humidity lend themselves to blight spread. Heck, even a thick fog can cause an increase in blight.

I’ve already seen a case of early blight in tomatoes (in my own garden, no less). This is the time of year to be looking for early blight (large spots on leaves with yellow circles around them.

Late blight is a possibility later in the season. It will appear as large blotches with dark purplish or black around them. It is also possible to get a fungus called septoria leaf spot (which Is on the same tomato as early blight at my house), which results in small brown specks on the leaves, which will eventually turn yellow and fall off.

Powdery mildew is also a concern, especially on cucurbit plants such as cucumbers and squash. You can identify it just from the name — you’ll see powdery white patches on leaves. These will eventually turn yellow and brown and potentially damage or kill the leaves. Downy mildew is another white fungus that appears on leaves and plant parts. It looks like a cottony fuzz up close. Both of these can affect many plants in the vegetable garden and landscape, so be on the lookout.

Sometimes people call in to ask me about their garden, certain that they have “the blight” on a plant in their garden. When I ask them to describe the symptoms, they describe yellow leaves on the bottom of the plant that eventually fall off. When I ask about the presence of spots or blotches on the leaves, they usually indicate that there are none. Is it a blight? Nope.

This brings me to the second rain-soaked problem in the garden: nutrient deficiency.

This problem arises about midsummer. Plants in the vegetable garden grow fast and require a fair bit of soil nutrition to keep healthy. The growth of the leafy, green part of the plant depends heavily on nitrogen.

When the plant has a nitrogen deficiency, it starts mobilizing the nitrogen from older leaves to feed the new ones, basically killing off the old to feed the new.

To avoid this problem, though, you need to strike a balance. Excess nitrogen can make plants sink so much energy into growing leaves and stems that they don’t have enough energy to bloom or set fruit. I can’t tell you the number of calls I’ve had about people with gorgeous, tall, leafy plants that produce nothing.

My suggestion to you is to use a moderate amount of nitrogen fertilizer early in the season, before plants bloom (this goes for both vegetables and flowers), then side-dress with a little bit of high-nitrogen fertilizer (such as urea or blood meal) after blooming has started. (Notice that I said “a little bit.” As with most things, more is not always better).

The third problem with all the wet weather we have been having is another nutrient issue. This time, the issue is calcium. A common issue with tomatoes, and several other fruits including peppers, tomatoes and squash, is blossom end rot. (Note to callers: Blossom end rot is also not a blight.)

Calcium is an important part of the cell wall structure in plants. When that breaks down due to a lack of calcium in the fruit, tissues can be damaged and result in the black damage we see on the end of the fruit. This deficiency of calcium can come from a few problems, including lack of calcium in the soil, too much nitrogen fertilizer (makes the plant grow faster than the calcium uptake can supply), too little water (calcium is brought into the roots with water), or damage to the roots caused by excess moisture.

Much of the work of absorbing water and nutrients from the soil is done by root hairs — tiny hairlike, single-celled projections from the root surface. Excess soil moisture will reduce the amount of air in the soil, leading to the suffocation of roots. The root hairs are the first to go, thus limiting the plant’s ability to take up calcium and other nutrients.

Aside from addressing the problems that cause blossom end rot, there’s little you can do once you observe it in the plant (it will likely produce more defective fruits). The best option is to prevent it by performing soil tests and making sure you have enough calcium with lime or gypsum, trying to make sure things stay evenly watered (though it is hard with excess rain), mulching to keep plants from drying out when there is no rain, and avoiding too much nitrogen.

As a last-ditch effort, you can try an application of a spray that has an easily absorbed form of calcium. You can usually find it labeled as a blossom end rot spray at the feed and seed store.

I’ve observed over the last few years that the loss of root hairs to excess rain has caused many plants in my vegetable garden to grow slower too. My garden usually looks and functions better after the rains have stopped and the plant grows new roots.

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