Caring for houseplants when temperatures are high, sunlight is intense, and the air is dry can be challenging. It involves not only getting watering right, but also increasing humidity, considering whether to move your plants to a better location, and knowing how to recognise when your plants are suffering from heat stress.

We hope our guide will help you to feel confident in caring for your plants and ensuring they thrive . . . even during a heatwave! 🌞

Watering Houseplants During A Heatwave 

One of the questions we are often asked is “Do houseplants need more water in the summer?” and our answer is always the same. It doesn’t actually matter what type of houseplant you are caring for or how high the temperatures get; you should never water your plants according to a set schedule. What you need to be mindful of is that, with increased temperatures, the soil your plants are growing in will dry out faster, so, first of all, you need to alter how often you check for moisture during a heatwave. 

Checking the moisture level in your soil is as simple as using your finger to feel the top 5cm of soil; if it’s dry, it’s time to water. However, if you don’t want to get your hands dirty, you could use a moisture meter or add one of our terracotta worms to your plant pots, then just pull him from the soil to see if it's time to water. 

When you need to water your houseplants during a heatwave, it’s important that you water deeply, early in the day and that you don’t use cold water straight from the tap. We always recommend using room-temperature water; if it's cold, it can shock plants, causing their roots to constrict, preventing nutrient uptake, and causing cellular damage. The easiest way to achieve this is to keep a jug or watering can filled with water overnight, so you will always have room-temperature water ready to use. 

Ideally, check the soil moisture of your house plants early in the morning, and if it’s dry, you'll have time to water them before temperatures rise towards midday. 

When you water, it’s all about watering deeply so that the whole of the soil becomes moist, allowing the roots of your plant to access the moisture. You can do this by using an indoor watering can, which enables you to efficiently deliver water around the base of the plant, easily navigating delicate foliage and tight spaces, whilst the slender spout delivers water without chance of overspill onto furniture or floors. 

If you want to keep the soil moist longer, you can always use mulch to cover the soil surface. Also known as ‘top dressing’, you can use something decorative, too. For example, for larger plants like Monstera, you could use pea shingles, decorative pebbles, or mini bark chips. However, for smaller pots, consider using sphagnum moss, crushed shells or decorative horticultural grit. 

Increase Humidity For Plants During A Heatwave

Many of the popular houseplants within the UK are moisture-loving, tropical plants, including Boston Ferns, Peace Lilies and Calatheas. These types of plants thrive in high humidity, and when faced with very high temperatures and dry air, as heatwaves bring, you need to find ways to increase humidity around your plants to help them survive and thrive. 

Group Plants Together

Grouping all your houseplants together during a heatwave is a simple way to increase humidity through transpiration. Transpiration occurs during the daytime when the leaf pores, or stomata, are open. As plants absorb water from the soil through their roots, it travels through the plant, delivering nutrients and helping to cool it, and it is released as water vapour through the pores on the surface of their leaves.

By grouping your plants together, you create a little ‘microclimate’ with the water vapour they release, increasing the humidity around them. 

Create a Pebble Tray

A simple yet highly effective way to increase humidity around a single houseplant or a group of plants is by using a pebble tray.

Creating a pebble tray is quick and easy. Simply fill a shallow, watertight tray or dish with pebbles, then add enough water so that it sits just below the top of the stones. Place your houseplant on top of the pebbles, ensuring the base of the pot remains above the water level.

This prevents the roots from sitting in water, which can lead to root rot. As the water gradually evaporates, it releases moisture into the surrounding air, creating a more humid environment that many houseplants thrive in.

All that's needed is the occasional top-up of water as it evaporates, making this a simple, low-maintenance way to improve humidity around your plants.

Use A Mister to Spray Your Plants

You will also find that some houseplants, such as Prayer Plants, Bird’s Nest Fern and Philodendrons, will all benefit from being misted when high temperatures create dry indoor air. For these plants, keep a mister close at hand so you can fill it with room-temperature water and mist them first thing in the morning to boost humidity. Doing this in the morning helps reduce water loss through your plant's leaves and cool the plant. As it’s only a short-term solution, your plant's foliage has time to dry before the shade and cooler temperatures of the evening. 

Don’t be tempted to think that misting your plant more than once will help your plant - only mist once, as excess moisture on your plant's foliage makes it more susceptible to fungal diseases. 

Have A Move Around To Give Your Plants More Shade 

The great thing about houseplants is that they are easy to relocate when the weather gets hot and the sunshine intense. 

“If you don’t like where you are: move. You are not a tree.”

If you have houseplants sat on south or west facing windowsills then these will get the most intense light so to prevent foliage from being scorched by the strong sun it’s best to either move them onto an east facing windowsill or if you can’t move them to a different windowsill fit some sheer curtains to diffuse the intense light. You should also get into the habit of rotating the pots every few days so that your plants have equal exposure to the light and this prevents constant sun on one side causing sunburn to that side. 

“Plants do not grow in rooms, they grow in habitats”

Regardless of what the weather is like, it is important if you want to be a good plant parent to ensure you have considered the best location for your plant - that’s in terms of light, temperature and humidity. Some plants which like high humidity can be more suited to being kept in a bathroom or kitchen where the humidity is usually higher. However, you will find some plants perfect for adding life into a shaded spot, such as a Golden Pothos which will adapt perfectly if housed in a shaded spot or north facing rooms. If you want some advice for finding the perfect spot in your home for whichever type of plant you have there is no better source of expertise than Kew and their practical card deck will help you find the ideal location for 60 different house plants. 

Signs Of Heat Stress In Houseplants 

Just like we can get more stressed during a heatwave, so can our houseplants. However, whilst we might get clammy, tired, find it difficult to concentrate, and complain about how hot it is, our plants show their stress in other ways and it’s important that we can recognise the signs and do something to help them.

“When I droop, you droop, we droop.”

When temperatures are consistently high then water will evaporate from your plant’s leaves faster than their roots can pull it from the soil. In order to prevent lethal dehydration your plant temporarily drops the water pressure in its leaves and they ‘droop’. Some gardeners compare this to your plants taking a little ‘siesta’ during the hottest hours as they perk back up once temperatures start to fall in the evening. 

"My fern was looking for a little 'glow up' and ended up in the 'crispy critter' phase."

Whilst it’s easy for us to protect our skin from getting burnt by applying sunscreen, our houseplants don’t have this luxury, and in intense heat, their leaves can get scorched. When this happens their leaves will develop bleached spots of pale yellow or white and this is often followed by the edges or tips becoming crispy and brown. You will see some houseplants actually curling their leaves inwards or downwards to try to protect them, so you may see your Peace Lily curling its leaves to shield them from bright sunlight or the thin leaves of Calathea may curl up on themselves in intense light. 

You will also find that some houseplants start to drop their leaves or flower buds to survive high temperatures. So popular flowering houseplants such as Hibiscus will begin to drop flower buds within 24 to 48 hours of temperatures exceeding 35 degrees celsius. They do this because they are entering survival mode, shutting down non-essential functions to conserve energy and reduce moisture loss. Whilst flower buds are more sensitive to high temperature than leaves, you will find that houseplants such as Anthuriums and Alocasias with their thin leaves will start to drop them within 3 to 7 days. 

First Aid For Heat Stressed Houseplants

Now that you can identify signs of heat stress in your houseplants, you will be glad to hear that if you act quickly, most plants will recover. However, recovery can be a long, slow process, and it may not always be successful and you are always better off taking preventative measures when a heatwave starts or, even better, when a heatwave has been predicted to alter how you care for your houseplants so that they avoid any ill effects due to increases in temperature. 

Want To Know More About Being A Plant Parent?

 We hope our advice helps you to be a Good Plant Parent, and if you need any further information on caring for houseplants, take a look at our selection of books, all designed to provide you with detailed information on some of the most popular plants and how to ensure they thrive in your home.And if you need a gift for a new ‘plant parent’, our Houseplant Care Tags would be perfect!

Happy Plant Parenting!  🪴