Humidity is a hot topic in the plant world right now. In many places, it’s the dead of winter. Many of you are running your heaters 24/7. Full disclaimer – I do not have to worry very much about humidity. Although it feels very dry in San Diego compared to Hawaii (where I grew up), we are close to the ocean. This provides significant humidity that is ideal for many of my plants. The humidity does periodically drop to lower than ideal levels. And, believe it or not, the temperature does drop to the 40s sometimes at night – that’s when we run our heater. But it’s not a huge problem for me. At the same time, I am fascinated by plant science, especially when there’s interplay with human science. And I love learning and researching new topics, so I took some time and dove in to this one.
Increasing ambient humidity prevents water loss from foliage. Putting water directly on leaves does not do this. In fact, having water sit on foliage regularly can increase the chance for disease such as fungal and bacterial infections. Standing water is, in general, not good for plants. And it’s not good for humans.
Up until recently, I used my cute little misters to periodically mist my calatheas and ferns. I would never spray the plant directly, just the air around the plant 2-3 feet away. But that only increases the humidity for a brief period of time – about 15-30 minutes maximum. In the scheme of things, it doesn’t do much. It may not hurt the plants, but theoretically it could. Thankfully I still get to use my cute misters for my tillandsias. (I like to soak them but if they are overdue for a soak and I haven’t had time, I mist to tide them over.) At the same time, I am not interested in having another device to maintain. Thankfully I think my plants will be okay because of where I live. I also use the grouping method (placing clusters of plants together around the home) which helps increase humidity around them. However, many of you really do need to consider humidifiers during these cold months. Read on.
The same way that standing water on foliage is not good for plants, standing water sitting in trays under plants or sitting in a humidifier can breed bacteria and fungi. These microbes can be aerosolized into your home. Keep in mind, there are bacteria and fungi (microbes) everywhere. Many of them are good; diversity of microbes can help keep “bad” microbes in check at lower counts. In fact, there is research going on about houseplant microbes helping keep human pathogen levels down. (But that’s for another time.) If you have standing water sitting around, it could allow for a small number of microbes to overgrow. For this reason, I don’t recommend trays with pebbles and water unless you’re sure you will empty and refill them regularly. Standing water could create issues for people with allergies, asthma, or immune conditions and is a breeding ground for mosquitos. Theoretically you could develop sensitivity to the fungi over time that you didn’t have before, due to repeated exposure. Additionally, if you don’t monitor your humidity levels (or get a humidifier that does that for you), you could end up with such high humidity that you have precipitation in the home and on your plants. I have actually seen black mold growing on walls in rooms where people have humidifiers set very high.
Here are some great articles listed below on the topic of humidifiers that I hope you will read if you are looking to buy one. I would recommend one that turns itself off if it gets to a certain level of humidity. Alternatively, you can get a hygrometer and check levels regularly. Consider placing it at least 2-3 feet from your plants and don’t direct the jet directly on to foliage. Be careful with humidifiers that use steam around kids. And please consider cleaning it very regularly (empty and refill most days, and thoroughly clean weekly) as the first article below explains, for the health of you and your plants!
Importance of cleaning your humidifier regularly:
Humidifier buying guide:
Good brief resource on misting:
Research on bacterial growth in humidifiers: