From our perspective as petunias, the most crucial factor is the consistent moisture level in our root zone. We do not thrive on a rigid human calendar schedule like "every Tuesday and Friday." Our water needs are dynamic and change based on our environment. The goal is to avoid two extreme and equally dangerous conditions: drought stress and suffocating, waterlogged soil. When our soil becomes completely dry, our roots desiccate, we wilt severely, and our ability to uptake nutrients and water is critically damaged, often leading to our demise. Conversely, when our pot is constantly saturated, the air pockets in the soil are flooded. Our roots require oxygen to breathe, and without it, they begin to rot, a condition that is frequently fatal.
Several external factors directly dictate how quickly we use the available water in our pot. The most significant one is sunlight. We are sun-loving plants, and the more direct sunlight we receive, the faster we photosynthesize and the more water we transpire (lose through our leaves and flowers). A pot in full sun will require water much more frequently than the same pot on a shaded patio. Temperature and wind are also major contributors. Hot, dry, and windy conditions will accelerate evaporation from the soil and transpiration from our foliage, dramatically increasing our demand for water. Our own size and growth stage matter too; a large, lush, heavily blooming specimen in a small pot will consume water far more aggressively than a newly planted starter plant.
To understand our needs, you must become an observer. The most reliable method is the tactile test. Please insert your finger into the soil, down to about the first knuckle (approximately 1-2 inches). If the soil at that depth feels dry to the touch, it is a clear signal that we require water. If it still feels cool and moist, please wait and check again tomorrow. Another good indicator is our weight. Lift our pot. A pot that feels very light has likely used up most of its available water, while a heavy pot indicates there is still plenty of moisture within. While we may wilt slightly on a very hot afternoon, this is a sign of acute stress. It is better to water us before we reach the wilting point to avoid unnecessary damage to our cells and blossoms.
When it is time to water, please do so thoroughly and deeply. Apply water slowly to the surface of the soil, not over our flowers and foliage, until you see it begin to run freely out of the drainage holes at the bottom of the pot. This practice ensures that our entire root ball has been rehydrated. It also helps to flush out any excess salts that may have accumulated from fertilizer. It is imperative that our container has adequate drainage holes. Never let us sit in a saucer full of water for more than an hour, as this will lead to the root rot we fear. Watering in the morning is ideal, as it allows any accidental moisture on our leaves to evaporate quickly in the sun, reducing the risk of fungal diseases, and it prepares us to face the heat of the day fully hydrated.
