Does It Matter What Time of Day You Irrigate with Drip Irrigation?

Available research suggests that the efficiency of drip irrigation is not strongly affected by whether irrigation occurs in the morning or afternoon.

Why You Often Hear "Irrigate in the Morning"

You may have heard recommendations for irrigating in the morning. This guideline is rooted in well-established practices for overhead or sprinkler irrigation systems.

With overhead irrigation:

• Water wets the plant canopy
• Leaves can remain wet when humidity is high in the canopy
• Morning irrigation allows leaves to dry during the day, reducing disease risk

However, many vegetable growers use drip irrigation, often with plastic mulch. In this type of production system, water is applied directly to the soil, leaving the crop canopy dry.

Why Time of Day Matters Less with Drip Irrigation

Drip irrigation works differently from overhead irrigation:

• Water is delivered directly to the root zone
• The canopy typically stays dry
• Evaporation losses are already low, especially in production systems using plastic mulch

Research shows that drip irrigation efficiency is not strongly affected by time of day, especially at deeper soil depths.¹

What Research Says About Timing and Crop Performance

Studies on the best time of day to operate drip irrigation systems are limited, but available research¹ suggests:

• No consistent advantage of morning versus afternoon drip irrigation for overall irrigation efficiency.
• For shallow-rooted crops, afternoon irrigation may maintain higher moisture levels in the upper soil profile during hot periods, potentially reducing water use.

The best irrigation timing depends on the crop and how irrigation is managed, so no single time of day is consistently optimal.

At the same time, most irrigation research focuses on soil moisture, irrigation frequency, and irrigation amount rather than time of day, reflecting the importance of these factors in irrigation management. ^2-4

Soil Moisture, Irrigation Frequency, and Irrigation Amount Matter More Than Time of Day

Soil moisture
The most important factor in irrigation timing is soil moisture in the root zone. Growers already use a range of effective approaches to determine soil moisture, including field experience, soil moisture sensors, and the feel method. These tools help determine when crops actually need water. Irrigation decisions are most effective when based on soil moisture in the root zone rather than on time of day.

Irrigation frequency and amount
How often you irrigate is also critical. The goal is to provide enough water to refill the root zone without moving beyond it. One way to approach this is to think of the "root zone as a cube." Water should remain within that zone. Too little results in plant stress, and too much leads to leaching and inefficiency. In most cases, it is more important to get the frequency and amount right than to focus on morning vs. afternoon irrigation.

Quick Guide to Determining When to Irrigate

1. Check soil moisture in the root zone.
2. Irrigate before plants show visible stress. If you see stress, crop performance has already been affected. Flowering and fruiting plants are more sensitive to water stress.
3. Aim to refill the root zone without over-saturating.
4. Adjust the frequency of irrigation based on weather conditions and crop stage.

Bottom Line

Drip irrigation gives you flexibility. The most effective approach is to maintain adequate soil moisture in the root zone by adjusting irrigation frequency and duration to match crop demand, while choosing a time of day that works for your operation.

If irrigating in the morning works well for your schedule, that's a good option. However, if crops need water, it's fine to irrigate at other times of day.

Sources

¹Adams, W.R., Zeleke, K.T. (2017) Diurnal effects on the efficiency of drip irrigation. Irrig Sci 35:141–157

²Patra, S.K., Poddar R., Pramanik, S., Gaber, A., Hossain, A. (2022) Crop and water productivity and profitability of broccoli (Brassica oleracea L. var. italica) under gravity drip irrigation with mulching condition in a humid sub-tropical climate. PLoS ONE 17(3): e0265439. 

³Yin, J., Yang, Y., Eeswaran, R., Yang, Z., Ma, Z., and Sun, F. (2023)  Irrigation scheduling for potatoes (Solanum tuberosum L.) under drip irrigation in an arid region using AquaCrop model. Front. Plant Sci. 14:1242074. 

⁴Zhao, H., Di, L., Guo, L., Zhang, C., and Lin, L. (2023) An Automated Data-Driven Irrigation Scheduling Approach Using Model Simulated Soil Moisture and Evapotranspiration. Sustainability 15(17):12908. 

This article benefited from AI (Microsoft 365 Copilot) assistance for language refinement and source identification.