Watering – Drench Versus Dunk

Water is the true driving force for growth, and a well-watered plant will grow and bloom better than one that is not as hydrated. Many orchid growers assume that leaving a plant submerged for an extended period will result in greater hydration than a simple watering. While soaking certainly has its place, orchid root physiology suggests that periodic drenching may be just as effective — sometimes more so and often more practical — for maximizing water uptake.

Orchid roots are designed to capture water quickly. The velamen, the spongy outer layer covering the roots, can become saturated within 30 seconds to a few minutes of exposure to water. Once saturated, water begins moving into the living tissues of the root and throughout the plant. Research and grower experience indicate that most of this uptake occurs during the first 15 to 30 minutes after wetting.

Because of this rapid absorption, the benefits of prolonged soaking diminish quickly. A one-hour soak generally provides only marginally more hydration than a 20- to 30-minute soak. Beyond that point, the roots continue to absorb water, but at a much slower rate as the plant approaches equilibrium.

Periodic drenching takes advantage of this same rapid uptake mechanism. A thorough watering saturates the velamen and root zone, initiating the same absorption process that occurs during soaking. If the roots are drenched again after they have begun to dry, the plant receives another opportunity for rapid uptake. In effect, multiple wetting cycles can stimulate repeated periods of particularly efficient absorption.

This mirrors the conditions under which many epiphytic orchids evolved. In nature, roots are rarely submerged for hours. Instead, they experience frequent rainfall, dew, or mist events that thoroughly wet the roots, followed by periods of drying. Orchid roots evolved to exploit these brief hydration opportunities.

There are situations where soaking can be beneficial. Severely dehydrated plants, orchids growing in highly water-repellent media, and species with exceptionally thick roots may benefit from extended immersion to ensure complete wetting. However, for routine watering, prolonged soaking often provides little additional benefit compared to a thorough drench.

For growers whose primary goal is maximizing water uptake, which maximizes growth and flowering, the evidence suggests that success depends less on the duration of a single watering event and more on achieving complete wetting of the root system whenever water is applied. Once the roots are fully saturated, repeated wetting cycles are often more effective than keeping them submerged for extended periods.

Other advantages of drenching over soaking is flushing fertilizer residues and plants wastes from the medium and aerating it. Consider these scenarios for two pots containing the same level of contamination:

Pot One is set into a tub of fresh water and allowed to soak for an extended period of time. Over that period, some of the contaminants, which are primarily deposited near the top surface of the medium due to accelerated evaporation, will dissolve in the water and be spread uniformly throughout the medium and absorbed. Meanwhile, being submerged, there is no gas exchange happening in the roots.

Pot Two is placed in the sink and a heavy “shower” of water is directed to the top surface of the potting mix. That “simulated rainfall” will mostly flush any contaminants down through medium column and out the bottom of the container. The motion of the water also entrains air, drawing it down through the mix, thoroughly oxygenating it at the same time.