Watering plants at night in cold weather can increase the risk of fungal disease on leaves and roots. In summer outdoor plants can benefit from water at night as it can help them to recover from a hot day, return water to the tips of their leaves and allow the deep roots to be thoroughly watered.
This article will explore the pros and cons of watering your plants at night. When you should avoid doing so and the benefits for your heat sensitive plants.
Watering plants at night in Winter
During winter it is best to avoid watering your plants at night. The roots can stay wet and cold and it increases the chance of fungal root rot developing. Splashing water on the leaves at night is also a bad idea as it could encourage mold growth.
Watering your plants at night in Summer
During summer it is fine to water your plants at night. Outdoor plants like tomatoes, basil and watermelon will thank you for a summer drink at night. At the end of a long hot day it can help to revive a drooping plant and cool the roots.
Watering your plants at night – Cons
Let’s start by covering why it is a bad idea to water your plants at night during the cooler months.
1. Soil will stay cold slowing growth
Watering plants at night will cool the soil temperature which is one of the signals that the plants receives to slow its growth. Cool soil could lead to slow growth, less leaves and a smaller plant in the long term.
2. Can cause root rot
Watering at night in the cooler month can lead to fungal growth in the soil and on roots causing root rot. This fungal growth can damage the roots and stop the plant from absorbing the nutrients it needs. This will affect plant growth and eventually kill the plant.
This happens more commonly in the cooler months where the soil stays wet for longer. In the spring and summer this is less likely to occur because the warmer temperatures, even at night will help the soil to gradually dry out.
3. Mold growth
As the soil stays wet for longer it can cause mold growth on the surface of the soil. This mold is generally not harmful to the plant but can look unsightly. This can look white or brown.
4. Can cause frost damage
Watering at night in the cold weather can increase the risk of frost damage. As water sits on the leaves for longer and the temperature drops, it can freeze on the leaves and cause damage.
5. Mold growth on the plant
Watering at night can leave water sitting on the leaves and stems. This can lead to mold growth the plant, the most common being sooty mold. This happened this year to my rosemary plant after lots of rain. This white or gray mold will cover the plant.
The plant can recover from the problem but it is important to reduce your watering, particularly at night.
Watering your plants at night – Pros
Watering your plants at night during the summer is actually fine to do. I do this all the time and my plants love me for it. Here are the top reasons why watering your plants at night is fine when the weather is warm.
1. Helps plants recover from a heat wave
The main benefit of watering at night after a long hot day is to help your plants to recover. Plants can dry, their leaves can burn and they can divert water from the leaves to the stems and roots. This can cause the plant leaves to droop in the heat.
Your plant will thank you for a long drink after a long, hot day. My tomatoes, strawberries and citrus trees all need a drink at the end of a summers day to keep them happy. They will be standing back up by the next morning after being watered at night.
2. Gives your plants more time to absorb the water
Watering at night actually gives your plants’ roots more time to absorb water. During the day, particularly when it is warm the water can evaporate quickly from the surface of the soil. Watering at night gives your plant a chance to absorb the water before it evaporates.
3. Plants need less water
Watering at night can actually save you water because it is absorbed well by the plant so you will need to add less. While water added in the morning evaporates out of the soil quickly on a hot day you plant will have a full 8 hours to absorb a night time water.
Again, this is fine in warm weather but when the weather is cool it can cause fungal growth.
It is ideal to avoid splashing water on the leaves of the plants even during summer to avoid fungal growth.
4. Water will reach the deep roots
Watering at night is a great way to give the water time to reach the deeper areas of the soil and the deeper roots. As the soil stays cool the water can slowly soak down to the lower layers of soil and encourage the plant to send deep roots down and increase its stability.
5. Water will evaporate off the soil slower
Watering at night will reduce the rapid evaporation that can happen when the sun is out. Watering when the sun is lower in the sky at the end of the day will give your plants a chance to get the water they need.
6. Avoids water sitting on the leaves can burning the plant
Leaving water on the leaves after watering during the day can cause leaf burn. The water droplets can reflect light and cause the leaves to burn even quicker. The plant will naturally divert water away from the leaf ends on a hot day causing the leaves to droop.
This is a natural process the plant uses to protect itself. At the end of the day if you give your plant a good water, the leaves will stand back up and your plant will be ready to face another warm day.
Watering your plants morning and night
In very hot climates some plants will need water in the morning and at night to survive a hot summer. Our tomatoes would need a good soaking in the morning and evening as temperatures in our region would soar above 100 degrees (F).
I also find that plants in small pots outdoors benefit from a morning and afternoon water. This is particularly true for my potted strawberry and even my young lemon tree.
Watering your plants at night | Summary
Watering your plants at night can cause problems if the weather is cold and the soil stays wet for a long time. Too much water at night can cause root rot, fungal growth and increase the chance of disease attacking your plant.
Watering at night on a hot summers day for outdoor plants is usually fine. I will do this for sensitive plants like tomatoes, strawberries, young fruit trees and plants in small pots.