Fall Rains

Let the Rain Fall

Our recent deluge of rain seems to be taking revenge for all those beautiful clear, sunny days of the previous summer. Being rain-free for so many days was a joy for gardeners, golfers, travellers or anyone wanting to spend time outdoors. Now we are all paying the price as low-pressure centers hover overhead and drop liquid precipitation on our gardens. As much as we complain about our dislike for the disruption and inconvenience of wet weather, it does have some benefits for plants.

Water is great in the fall to give broad-leaved evergreens a better chance of making it through the winter (alive and preferably also healthy). Broad-leaved evergreens are the plants that keep their leaves all year round (under normal circumstances). Hollies, euonymus, boxwood, cotoneaster, English ivy, kalmia, mahonia, pachysandra, pieris, pyracantha, rhododendrons, and vinca all fit into the general classification of broad-leaved evergreens. These plants are popular because they have a different look in the garden than the narrow leaved conifers. They also add much needed visual interest in the garden during the winter. Broad-leaved evergreens do need some extra protection during the winter from the damaging effects of sun and wind. Fall rains can provide some of this protection. During the winter, broad-leaved evergreens are constantly loosing moisture to the air. This moisture cannot be replaced once the soil is frozen. Bright sun and strong winds cause more moisture to be lost than normal. The result is winter burn or sun scorch, which causes the leaves to turn brown around the margins and sometimes progress inward. If plants are well stocked with water in the fall, then there’s a greater margin before damage is done.

Rainwater in the garden also helps speed up the composting process. An ideal compost pile should be as damp as a wrung out sponge. This moisture plus frequent turning and the appropriate ratio of carbon (browns) to nitrogen (greens) hastens the composting process. Watch out for too much water (or rain) when the whole composting process could turn into a smelly anaerobic decomposing mess.

Rainy days keep most gardeners out of the garden. This lets gardeners focus on other important aspects of their life (like spouses and offspring). In October when it is more likely to rain than not, the weather allows for regrouping indoors. This time could be used to make plans for the excess vegetables waiting to be harvested. Some of these are always all those unripe tomatoes. Incidentally, being inside during the rain is a great time to surf the Internet and read garden blogs.

A dreary, grey day full of rain is the best time to venture outside and see the fall colours. This type of weather brightens and intensifies the colours of the trees. The view out of a rain-smeared windshield also adds to the atmosphere. Here vivid yellows seem to glow and scarlet colours shimmer more in the rain. The glossiness of the wet leaves upon closer inspection adds another attractive feature.

To gardeners, nitrogen is one of the most important nutrients for plants to keep them happy and healthy. Nitrogen results in larger plants and increased yields. It is one of the macronutrients that need to be replenished the most in the soil because some nitrogen leaches (washes) away with the rain. Ironically, one handy supply of nitrogen is courtesy of the stormy clouds overhead. Some of the nitrogen in the soil comes from lightning in the air that travels with the rain droplets.

Cleome (spider flower) after the fall rain at Temple

Cleome (spider flower) after the fall rain at Temple

The air is naturally full of nitrogen. In fact 4 out of every 5 molecules in air is nitrogen. Unfortunately, this form of nitrogen is not much use to plants. The mystery of how nitrogen in the air is changed into usable nitrogen in the soil involves the heat of lightning. Lightning heating up the air forces nitrogen gas to bond with oxygen. This creates nitrogen oxides. These mix in the air, dissolve and fall out with the rain landing at plant roots as a usable form of nitrogen (called nitric acid). Lightning produces a small percentage of the total nitrogen oxides around the world. Cars and power plants that burn fossil fuels produce the bulk (a cause of acid rain).

Lightning does not have to crack overhead to bring nitrogen to the garden. Lightning in the vicinity will spread out and land throughout the neighbourhood. Every day lightning strikes the earth over 8 million times somewhere around the surface of the planet. Interestingly, one good lightning storm can supply between three and ten percent of the recommended year’s supply of nitrogen for the lawn. More than ten storms during the summer and the lawn may not need any commercial fertilizer.

Rain is great for cleaning off the dirt that the wind picks up and deposits on plants. This layer of dust is easily removed with a steady or heavy rain. The plants look better and they will grow better if dust is not clogging their stomata (breathing pores). Stomata are found on plant leaves and are an important opening for gas exchange to occur.

Fall rains may also bring about some plant health benefits. Some plant pests are chased away by moisture on plant leaves. The two-spotted spider mite is one of these. It is at its optimum reproductive speed when temperatures are at 86 F. (30 degrees Celsius). At this temperature under dry conditions mites reproduce every eight days. In the fall when temperatures drop to 53 F. (12 degrees C.) and the rain is falling, the mite takes 6 weeks to reproduce. Rain is a great pest control measure for any plants that are bothered by spider mites.

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