Winter is here! With colder temperatures and shorter days our beloved houseplants will need an extra hand to make it through the season. Most of our houseplants (like Monsteras and Philodendrons) are native to (sub)-tropical regions, where winters are not as chilly as in Europe. So the colder season can be a shock for our lush friends, and there is often confusion on how to help them survive until spring arrives. In this blog post I will summarize all the keynotes you need to consider when caring for your plants during these chilly times, and to not make silly mistakes.

What’s so different during winter?

To understand what our green companions require during winter, we first need to sum up how the colder season affects the plants environment.

Obviously, it’s colder outside, this should not have a massive effect on your plants health if your heating is on and it stays around 18-21°C in your house or apartment. This temperature is still not optimal for much growth, but the plant will not be stressed by cold within this range.

A bigger issue is the length of days and the availability of light. As we all know as veteran plantkeepers, plants get their energy from the sun: Chloroplasts within the cells capture light and convert it to energy in the shape of sugars. These sugars are then be used fulfill the plant’s needs, like basic functions to stay alive, growth, pest and disease resistance etc. To create such sugars the plant requires 3 crucial components: capturing CO₂ through the stomata, water uptake through the roots, and light-energy to perform the chemical reaction within the cells. As the available light diminishes during winter (due to shorter and darker days) the plant has less energy to do the work, and hence will need less resources (water and CO₂). You can compare it with making a cake, when you have all the ingredients (flour, eggs, sugar, butter etc.) and make the batter but your oven does not have energy. It will probably not be possible to make that cake. Meanwhile your ingredients start spoiling and smelling in the fridge until you wait for sufficient energy to make the oven work.

The last issue is humidity: while we are heating our homes with radiators the water content in the air of the rooms goes down to a humidity of 30% or lower. Most tropical houseplants thrive 50-60% humidity, so we can see how this can lead to problems. When the air is dryer, it will suck more water out of the plants and potted soil. This can make the whole watering issue that much more confusing. On one hand the plant needs less water (because of a lack of energy to use it) but more is extracted by the surrounding, dryer air. Let’s start balancing things out and get to some points of action!

Preventing silliness

Let’s help you out to prevent some silly mistakes. The biggest problem during winter is overwatering, often people keep the same watering routine that they had during summer, but since the plant can not use all that water in winter, it will sit in the soil and rot the roots. Especially in winter, it’s better to not water enough than to do it too much! Lets break down all the crucial factors though: Light, water, temperature and humidity.

Chase the Sun: Light

As light availability is the biggest threat to your plant during winter, it’s important we help them along:

• Move them closer to a window (south – or west-facing), here they will already be closer to the source!
• Wipe the dust of the leaves. Accumulated dust on the leaves creates a boundary for the little available light to get to the chloroplasts, as well as blocking the stomata (for CO₂ uptake) and attracts pests. So wipe of that layer of dust to boost the photosynthetic capacity of your plants. Do this carefully with a soft, damp cloth and avoid using chemicals except for maybe a natural soap. Don’t forget the undersides of the leaves! While you’re here wiping away, you can also do a quick pest check to make sure your plant is not hindered by pesky insects during these crucial times.
• If light is extremely scarce in your home, you can think about investing in a grow light. The best option here is a full-spectrum light to mimic the sunlight as closely as possible.

Less is More: Water

As light (energy) is less present, the plant will need less water to function (compared to the growing season). Overwatering and resulting root rot is the main reason plant owners lose their babies during winter. Here are some tips to prevent that from happening:

• Test the soil before watering. You can use the ‘stick a finger in and see’-technique but we do not endorse this. Dry air from heating might have dried the first layer of soil, but underneath it may still be wet! That’s why we recommend the ‘pot-lift’ technique'. Often you can feel that that the soil is still moist based on the weight of the pot. This requires some training but is more accurate when trying to guess the amount of water still available. 
• Optimize drainage by opting for a well-draining substrate and a container with drainage holes. This will improve water circulation and reduce stagnant water around the roots.
• Increasing humidity around the plants can also help! More about that later!
• When watering, do not use cold water from outside but stick with room-temperature to avoid shocking the roots.
• Watch out of signs of overwatering! Yellowing or browning of the lower leaves is often the first sign of a watering problem. Prevent a waterlogged soil.

Keep it Cosy: Temperature

As long as it is not freezing cold in your house, your plants will be fine with a little drop in temperature overall. There are still some important points to consider:

• Avoid extremes! Do not place the plant near open windows or doors where sudden blasts of cold air can strike it. Do not place it near the heater either, as this will be too warm and too dry for the plant to be healthy. Try to keep your plants in a location with stable temperatures.
• When you’re plants are close to the window, be careful that they do not touch the chilly glass itself. Touching cold surfaces with their leaves or stems can cause browning and loss of the organ.

Winter Tropics: Humidity

The humidity in homes during winter is reduced a lot when heaters and radiators are on. To reduce the dryness of the air around your plants there are several tips we can give you:

• Do not place your plant near the heater!!
• You can create a microclimate of higher humidity when you group your houseplants together. The air within and around this grouping will be less dry, due to the transpiration of water the plants release to the air, helping their buddies when grouped.
• You can make a little pebble tray underneath the pot to increase humidity, a guide can be found here. 
• Misting plants during winter is tricky, it can increase humidity but may also leave droplets on the leaves. In colder temperatures these droplets can lead to fungal diseases. If you want to increase humidity “manually”, it’s better to opt for an humidifier.

And what else?

Apart from the big 4 factors, there are some extra considerations to make during winter:

• Prune and clean: Trim away yellow/brown leaves to help your plant conserve energy for healthy growth.
• No repotting: Repotting causes a lot of stress for the plant, a stress it can definitively do without during the colder months. It’s better to repot in spring or summer when the plant is actively growing.
• Fertilize sparingly: As your plants are mostly dormant, it will not need extra nutrients for growth. If fertilizer is left un-used in the soil it can become toxic and cause more harm than good. It’s better to hold off on fertilizer, but if necessary only put a very small amount and heavily diluted.
• Pest check: Dry air due to heating can attracts pests like spider mites and mealy bugs. Check the leaves regularly to prevent infestations. A pest can be the last drop in the bucket for the plants longevity during cold months, so better to prevent than to cure!
• Leggy growth: If your plant starts stretching out and become more stick/leg-like, it is time to move it closer to a window. Stretching of organs often happens when plants are looking for more light, so best to help it out a bit!

Chill, you’ll be fine!

If you follow these tips and tricks your green buddies should make it through the winter months just fine. By understanding the role of light and how it impacts the health of your plant you can now make some educated changes for taking care of them when light is less available. Every plant is different, and it will be important to keep an eye out! But by preventing silly mistakes you can make sure your houseplants thrive until the next growing season, so good luck and stay warm!

Your inhouse biologist,

Senne