Garden Watering Wisdom: Techniques for Healthy Plant Growth

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    Some gardeners have trouble deciding when to water. Like us, plants are mostly water. The availability of water can be a significant limiting factor in plant growth.

    Plants use water for photosynthesis and cellular respiration, for structural support (turgor pressure), as a solvent, and as a solution to transport food and nutrients. Water is present in every cell. Like people, plants suffer when they don’t get enough water and can “drown” or not be able to get enough oxygen when there’s too much water.

    While in nature, a plant must make do with what it can get, in our gardens we can provide a more curated environment, enabling our plants to grow, flower, and fruit to the best of their ability. A wild plant shuts down when water is scarce. We’d like ours to keep making more tomatoes.

    Factors Determining Plant Watering Needs

    Several factors will influence how often your garden needs watering, whether in the yard or on the balcony. No two gardens will be the same. From the weather to the soil and the plants themselves, watering needs change over time. Here are a couple things to keep in mind.

    Soil Types

    Your soil type and the level of organic matter in the soil will play a large role in how often your garden needs to be watered. Generally, the more coarse your soil texture, the better the drainage, which means watering more often. If you’ve been to the beach, you’ve seen this effect. Water drains almost instantly from the sand after a wave washes up.

    Finely textured soil that holds too much water doesn’t allow gasses to exchange, which suffocates the roots. That’s how excessively wet soil can drown a plant–it deprives the roots of oxygen. Clay soils with slow drainage will need watering less frequently than sandy soils.

    • Sandy soils drain very quickly and typically also have low organic matter.
    • Loamy soils drain moderately and often have a high percentage of organic matter.
    • Clay soils are famous for holding onto water and having poor or slow drainage. While fertile, they can be problematic in this way.

    The amount of organic matter in your soil also affects how often you need to water. The bits of old leaves, sticks, grass clippings, humus, and other formerly living material slowly decomposing in your soil act like a sponge–they hold water and release it slowly. With a high amount of organic matter, your soil will soak up much more water that otherwise would have drained away or run off on the surface. It’s part of the reason we add compost to our gardens–we want more soil organic matter.

    Remember container plants need watering much more often than their cousins in the ground. While potting mix often contains ingredients to store water, the soil in pots dries more quickly for multiple reasons. Plants outdoors in containers often need to be checked and watered daily.

    Plant Type and Size

    When watering, think of plants in several categories: those that like water, those that don’t mind drier conditions, and those at home in the desert. Adapt your watering frequency to match their preferred soil moisture. Here are a few examples.

    • Water lovers: tomatoes, peppers, melons, basil, mint, dahlias, most annual flowers.
      Keep the slightly damp.
    • Enjoys some drier conditions: many cooking herbs like rosemary, thyme, oregano, and
      many perennial flowers like echinacea, black-eyed Susan, or yarrow.
    • Thrives in dry soils: succulents, prickly pear cactus, and other similar plants.

    Naturally, larger plants (of the same species) use more water daily than smaller plants. When you plant a young cherry tomato in a pot in late spring, it doesn’t need watering as often. The large, bushy, fruit-laden plant it becomes by late July may need watering twice daily.

    How You Know It’s Time To Water Your Plants

    Eventually, the plants will tell you it’s time to water. You’ll recognize their droopy, wilted appearance and instinctively know. But, cycles of dehydration can cause stunted growth and poor plant vigor. We’d rather catch it before that.

    Of course, keep an eye on the weather. Your plants won’t need as much water during a cool, cloudy week as during hot, sunny, windy conditions. A rain gauge is a fantastic tool to help you quantify the weather. While the local meteorologist might estimate how much rain fell in yesterday’s storm, precipitation varies widely over distances as short as a mile. A good rain gauge can tell you if that overnight shower dropped only an eighth of an inch (not enough) or 1.5 inches (a good, long drink that should last a few days).

    But perhaps the best way to know when your plants need water is to get your hands dirty. Stick your index finger in the soil under the plant as deep as you can thrust it. Or, grab a handful of soil. Damp soil with water available for plants will be darker, cooler, and you’ll be able to feel there is moisture. If the soil is dry and warm, dusty, or light in color an inch down, it’s time to water.

    How Much to Water Plants

    For container plants, this part is easy. When they need it–use the finger test above–slowly provide water at the base of the plant until water trickles out the drainage holes in the bottom. If you’ve allowed the plant to really dry out, the potting soil may refuse to absorb water at first, and all the water will rapidly run out. If that’s the case, you’ll need to patiently keep watering until the soil rehydrates.

    For gardens, we want to water deeply, and less often, instead of frequent shallow waterings. Watering deeply encourages plant roots to expand. Use your finger or a trowel to check, and keep watering until it has soaked in several inches or more.

    The general guidance for outdoor plants is that they’ll need an inch of water per week. It’s a good place to start. However, you’ll need to adjust for hot weather and heavy production–think rapidly growing corn, heavy crops of tomatoes or squashes, etc.

    If overhead watering, use your rain gauge as a measuring tool, and remember to feel the soil. Don’t panic if you forget and leave the sprinkler on overnight. Mother Nature sometimes waters the garden all night too.

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