Guttation – Droplets on the Leaf Edges

Sometimes, usually overnight or when the weather is cool and damp, droplets of liquid form along the edges of the leaves of plants. This is “Guttation”. Not to be confused with the early morning dew, guttation is caused by the “water potential” in the roots of the plants. Because transpiration doesn’t occur at night or in the damp when the plants stomata are closed, if the soil is wet, the pressure of water trying to rise up through the plant can’t evaporate so its forced out through special glands at the edges of the plant.

Is this bad for the plant? Not really, its part of the normal process of growth. However, there are three things that could cause harm to the leaves. Firstly being damp, fungal spores (such as blight) are more likely to settle on the leaves and infect the plant. This is made worse by the fact that Blight is encouraged by high humidity and warm weather so, if its damp and warm you’re best not go into the greenhouse if you might have blight spores on your clothes. Secondly, if the sun suddenly springs into life, droplets of liquid can focus the suns rays and burn the edges of the leaves (this is also a reason not to get leaves wet when watering). Finally, the liquid contains nutrients and (if you’ve been overfeeding your plants – a relatively common fault of all amateur growers) the edges of the plant could get nitrogen burn which can be mistaken for a number of other problems.

Should you try to stop it? Giving your plants the right amount of water (enough to stop them wilting but not enough to drown them) will reduce guttation but then you need to be able to predict the weather better than I can.