Rhubarb is a perennial vegetable that thrives in cooler climates and is renowned for its tart stalks. Because it produces massive leaves, it requires a consistent supply of moisture to support its large surface area and maintain healthy growth. Rhubarb is also considered a “heavy feeder,” relying on a healthy root system to draw up significant nutrients and water throughout the growing season.
Watering Requirements for Newly Planted Rhubarb
The first growing season is a vulnerable period for rhubarb plants, whether newly planted crowns or transplants, as they work to establish a strong root system. Because their roots are shallow, they cannot draw moisture from deep in the soil and require high-frequency watering. Aim to keep the soil consistently moist, providing water one to two times per week during periods without rain.
The goal of these early waterings is for the moisture to penetrate the soil to a depth of six to twelve inches, ensuring the developing roots are thoroughly soaked. Apply water directly to the soil surface around the plant to avoid wetting the leaves and potentially encouraging fungal issues. Maintaining this regular schedule throughout the first year is necessary for the plant to build the vigor it needs for future production.
Routine Hydration for Established Plants
Once a rhubarb plant is established—typically by the third growing season—its watering requirements shift to a less frequent, but still deep, schedule. Mature rhubarb develops an extensive, deep root system that makes it moderately drought-tolerant; however, prolonged dry spells will severely reduce stalk production. The general guideline is to provide the plant with approximately one inch of water per week, either from rainfall or irrigation.
When watering, use a deep soaking method to encourage the roots to grow downward. The water needs to permeate the soil to a depth of at least 12 inches to fully benefit the mature root ball. To check this depth, insert a trowel or soil probe several hours after watering to confirm the moisture level. During periods of high heat or drought, a thorough drenching every seven to ten days is adequate to maintain productivity.
Diagnosing Water Stress (Too Much or Too Little)
Identifying water stress can be tricky because both overwatering and underwatering can lead to similar visible symptoms. The most common sign of distress is wilting, which occurs when the plant cannot take up enough water, either because the soil is too dry or the roots are damaged. If the plant is wilting, the first step is to check the soil moisture.
If the soil is dry several inches down, the plant is underwatered, and the leaves may appear curled with dry, brittle brown edges. Conversely, overwatering often causes leaves to turn widespread yellow, and the stalks may feel soft or mushy due to root rot. Overwatering is the more serious issue, as waterlogged soil starves the roots of oxygen and can lead to fatal crown rot.
Modifying Watering Schedules Based on Environment
The watering schedule requires routine adjustment based on environmental factors. Soil composition is a major variable; sandy soils drain quickly and necessitate more frequent, shorter water applications to maintain moisture. Conversely, heavy clay soils retain water longer and must be watered less often to prevent the waterlogging that leads to root and crown rot.
External conditions like high temperatures and wind increase the rate of evaporation and transpiration, requiring an increase in watering frequency. During extreme heat, even a well-watered plant may temporarily wilt, which is a natural defense mechanism. Using organic mulch, such as straw or compost, is recommended, as a thick layer dramatically reduces soil moisture evaporation and keeps the root zone consistently cool and damp.