How Do I Tell if My Plants Need Water?

The need for irrigation depends strongly on the growth medium used and on how compacted the medium is. Waterlogging from overwatering is very detrimental to plants and attracts pests. Irrigation needs can be highly subjective based on the type of plant, the growth stage of the plant, and the greenhouse temperature and humidity. During vegetative growth, the plant’s need for water fluctuates before stabilizing in the flowering phase. 

Watering Frequency and Irrigation

Soil moisture meters or sensors can give some indication of the possible need for watering but can be unreliable if moisture is unevenly distributed. When determining if plants need watering, moisture meter readings, temperature, humidity, and light intensity should be considered along with sensory evaluation and experiential knowledge. 
Higher humidity reduces the need for watering. In naturally humid environments some plants may even be cultivated without irrigation. Most modern growers will utilize irrigation systems in their greenhouse though. Many mature plants can be watered about three days apart, others may need more frequent watering. Seedlings and vegetative plants may require more or less frequent irrigation since their needs are more variable. During germination, the seedling trays usually require daily watering.

How to Tell if Your Plants Need Water

  • Container weight is commonly used to determine the moisture level and when to water. If pots feel heavy, even though the surface is dry, do not water. If pots are light, even though the surface looks wet, feel below the top of the soil to see if the soil is wet in the lower portions.  
  • Moisture sensors can be used and are able to connect to automated irrigation systems.
  • When watering, bring the water to container capacity (the point where the soil cannot hold any more water against the pull of gravity). This will encourage deep root growth.
  • About 10% of the water applied to a pot should leach and run through to help remove any excess salts in the soil.
  • Signs of underwatering plants: Wilting, dry soil, slow growth, discolored leaves (yellow, curling, dry edges)
  • Signs of over-watering plants: Soil is wet and muddy, wilting, leaves turning brown, signs of mold, blisters or lesions on plant, yellow drooping leaves, root rot
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