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How to keep your houseplants healthy

The sale of indoor houseplants soared during the COVID-19 pandemic as people were confined to their homes and needed to remind themselves of the beauty of nature. Green spaces are known to be beneficial to mental and physical health, and confer a sense of wellbeing, and people love to bring a bit of that greenness into their homes by means of attractive plants in pots. Interestingly, many of the most popular pot plants have strange roots that grow out of their stems and seem to live comfortably in the air, rather than in the pot’s soil. 

These are known as aerial roots, and a new study published in the journal Plant, Cell & Environment suggests that they are capable of elevating the health of our indoor plants, as long as we pay them some attention. Just like underground roots, aerial roots can absorb nutrients and water, although the relative importance of this to the plant had not been investigated. 

Researchers from the University of Nottingham decided to grow houseplants that have both aerial roots and roots in the soil, and to compare the uptake of nitrogen by the two different types of roots. Nitrogen is used for forming proteins and so is essential for healthy plant growth.

“Houseplants are really important for improving air quality and bring mental health benefits, but many people struggle to know the best way to look after them. The main focus is usually on feeding them in the soil with regular watering and plant food, but what many people don’t know is that many plant varieties have roots along the external stems that need our attention too,” said Dr. Amanda Rasmussen, who led the study. “We wanted to test if these roots do take up nutrients and if so, find out exactly how much they can take up to improve the health of the plants.”

The researchers used three different species of plants that are commonly kept in pots in homes and that have aerial and below-ground roots: Anthurium andreanum, also known as flamingo flower; Epipremnum aureum or devil’s ivy; and Philodendron scandens or sweetheart plant. They grew these plants in custom-made growth chambers under conditions of high humidity and ambient humidity for three months. Both aerial roots and soil-formed roots were fed mixtures of the nitrogen-containing compounds known as nitrate, ammonium and glycine, and growth and physiology parameters were measured weekly.

The results showed that aerial roots were consistently better at taking up nitrogen than soil roots, and it didn’t matter which form the nitrogen was in. All three forms of nitrogen were absorbed more readily by the aerial roots. This was contrary to expectations as the aerial roots are thicker than the soil roots and therefore have a smaller surface area to volume ratio. The researchers had expected the thin soil roots to be better adapted to absorbing nitrogen. 

The experts had also expected that the plants would absorb nitrogen in organic form (ammonium and glycine) in preference to nitrogen in inorganic nitrate form. But the plants absorbed all three forms of nitrogen equally well. In addition, all three species of plants grew better in high humidity conditions, with aerial roots showing the greatest increase in biomass. 

“The results of this study are really exciting as they could transform the way we feed certain types of plants and help us to keep them healthy and thriving! A simple spray with water and some plant food to the aerial roots may help optimize the amount of nutrients the plant gets and will ensure we can enjoy them to their fullest for many years,” said Dr. Rasmussen.

The authors state that there is a need for future studies involving more different plant species and a wider range of nutrients. They also feel that the growth of plants with aerial roots can be enhanced by the use of misting and the addition of foliar applications of fertilizers that coat the aerial roots. Instead of ignoring these strange structures that sometimes appear to grow upwards instead of downwards into the soil, plant owners would do well to pay attention to their needs, thereby ensuring healthy and long-lived plants. 

By Alison Bosman, Staff Writer

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