Your gardening questions answered: Will a dehumidifier damage my plants?

Q: Please can you tell me if a dehumidifier is bad for house plants? On the advice of a friend we recently got one as an eco-friendly, cost-effective alternative to a tumble drier. It’s great when it comes to drying the laundry and getting rid of condensation, but I’m worried that it might not be so great for my plants! M Pearse, Dublin

A: This is an interesting one. As you say, dehumidifiers are increasingly being used in many Irish homes as a relatively cheap, planet-friendly way to dry clothes, as well as to reduce humidity levels in houses where condensation and damp might be a problem. Some of them can also filter dust and allergens from the air. While all of this is great in terms of human comfort and good health, the problem for houseplants is that most of them don’t really like the air to be too dry.

So, you’re right to be a little concerned about the welfare of your houseplants, especially if you’re regularly using your dehumidifier at a laundry mode setting specifically designed to dry clothes, where the target humidity level is going to be significantly lower (usually around 35 per cent) than it would be when the machine is simply being asked to lower room humidity to appropriate levels (usually 45 per cent-50 per cent).

Depending on the species of houseplant, some will struggle more than others if the humidity in the room that they’re growing in is suddenly dramatically lowered. The popular maidenhair fern (Adiantum sp), for example, needs a mild, very humid atmosphere (greater than 60 per cent humidity) to be happy, whereas a fleshy succulent like Aloe vera will tolerate much lower levels of humidity.

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For this reason, I’d be inclined to move any humidity-loving species from a room where you’re regularly using your dehumidifier to dry laundry. No matter what the species of houseplant, you’ll also almost certainly need to water yours more often than normal at this time of year, as the compost is going to dry out more quickly in any room where the dehumidifier is in regular use. Regular misting of their leaves will also help, as will grouping your houseplants together, placing shallow ‘wet trays’ beneath the pots filled with pebbles and water to increase humidity levels immediately around the plants, and covering especially vulnerable plants with glass cloches or bell jars (lift these occasionally to refresh the air).

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Watch out for signs that your plants may be suffering as a result of overly low levels of humidity, which include curling of leaf edges, browning, scorching or crisping of their leaves and wilting. Lastly, also bear in mind that regular use of your dehumidifier is likely to affect the vase life of fresh cut-flowers as well as any fresh seasonal decorations such as Christmas trees, foliage swags and seasonal wreaths.