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How much water do my houseplants need in winter?

By Anna Gervai |

My first spring and summer of owning a significant number of plants was spent blissfully unaware of what was to come.

The worst dilemma my indoor jungle had caused me thus far was how to fit everyone around the sink at watering time. I played the plant shuffle like clockwork every weekend, watering to a routine. (If it weren't for such a warm house bathed in bright, natural light, I would have been in big trouble that summer, let alone winter ¨C I'm shocked I didn't lose more plants to root rot.)

As temperatures started to drop, I started to worry though. Would my plants survive?

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Indoor plants, houseplants
Some of Anna Gervai's plants bedded down for the winter in their UV warm case. (Stuff)

Kellie Vince ¨C known as @thelittleplantfairy to her 25,000 followers on Instagram ¨C shared the same concerns. "My first winter with houseplants, I lived in a big old villa and was constantly moving plants around, chasing the sunshine. I was so worried they weren't going to make it."

Blessed with a warmer climate in winter and ample natural light is Kate Hickey, who shares her Whang¨ˇrei home in New Zealand with more than 100 plants in her personal collection; she also maintains more than 500 indoor plants in her greenhouse for her business, Wildvine The Shop.

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At the other end of the North Island, Linh Tong prepares her 100-plus houseplants for winter by turning on the grow lights. "It can get pretty cold and gloomy in Wellington. Some of my fussier tropicals like my calathea suffer a bit in winter, but now live in my main bathroom where the extra warmth and humidity keep them happy."

With the varied conditions throughout New Zealand and Australia, the same rules don't apply to everyone. You do need to take your conditions into account, which is why hobbyists have sometimes very different approaches from each other.

Indoor plants, houseplants
Houseplant enthusiast Linh Tong with a Philodendron 'Pink Princess' in her Wellington home. (Stuff)

Watering your houseplants in winter

Don't make the mistake I did in the beginning of my plant parent journey. Watering to a schedule is never a good idea, especially in winter.

Less than 5 per cent of water roots take up stays in the plant, with as much as 99 per cent of the water we give our plants lost during transpiration. Light, warmth and airflow all increase transpiration, the process of water moving through our plants, which is mainly lost as water vapour through small holes on the surface of their leaves, called stomata.

Stomata also take in carbon dioxide and put out oxygen. But with shorter daylight hours, weaker sun, colder temperatures and reduced airflow with houses closed up over winter, transpiration reduces, and our plants take longer to use up the water in their pot.

Those winter changes add up to the biggest risk for indoor plants: root rot. The most important change most of us need to make in winter is to reduce the frequency of watering.

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indoor plants
Grouping houseplants together in winter can help increase the humidity around them. (Getty Images/iStockphoto)

Overwatering doesn't mean how much water you give your plants, but how often. That common misconception caught me out in the early days.

When you do water, check that your water temperature isn't too cold. Cold water can damage roots, also leading to root rot.

Although not much has to change at Kate Hickey's Whang¨ˇrei home over winter, watering is one habit she does adjust when caring for her houseplants. "Less is more. Wet and cold is a match made in heaven for root rot. A great, chunky soil mix is also key for holding less water," she says. "I wait until a plant's soil is completely dry if the plant can handle that. I water in the morning and use warmer water so as not to shock the roots."

One of Hickey's watering tips is using clear nursery pots. "Hands down, clear pots have absolutely changed the game in terms of monitoring moisture levels for my plants."

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Houseplant
Check plants before watering, especially in winter, to keep them healthy. (Getty Images/iStockphoto)

One lesson I learned the hard way my first winter is to watch out for the top of the soil feeling dry while underneath, the soil is still wet around the roots. Artificial heating in winter can dry out the soil surface, fooling you into watering again too soon, increasing the risk of root rot.

More than 250 plants now call Vince's Taranaki house their home. She's better now at recognising her plants' varied needs, but in the early days there was a big learning curve. "I was lethal at overwatering back in those days. If a plant didn't look happy, I would give it water. Sadly, due to inexperience I lost a few plants."

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The one tool she recommends for fewer winter worries is a water meter. "I use one all year round. It takes away the guesswork."

She doesn't use any special lighting. "My plants pretty much go dormant over the coolest few months so I adjust my watering instead."

Winter is when tools like water meters can become life savers. Wellington-based horticultural technician Shayna Robinson was inspired by friends and family struggling with the same issue, to create her own New Zealand-made water meter called the GrowProbe. "Overwatering is such a common issue, or too much love as I call it."

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Warm, but not dry

Most popular houseplants come from tropical climates where it stays above 25ˇăC all year round, it's not surprising our winters can be a struggle. Most indoor plants enjoy the same temperature range we do: between 18ˇăC and 25ˇăC. Some are more cold-tolerant than others and can handle drops to 15ˇăC or even 10ˇăC.

I shift all my indoor plants that I can to one room over winter and give them their own heat source. My go-to is an oil heater set to 18ˇăC.

My more cold-sensitive plants, including propagations and baby plants, get special treatment and shift into a cabinet over winter, sort of like an indoor greenhouse.

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Take care with heat pumps, fan heaters and fireplaces. Some heat sources radiate heat further than you might think. I've had plants I thought were out of reach end up with scorched leaves from heat-stress.

Temperature is less of a concern in Hickey's Wh¨ˇngarei home, but she finds that one plant needs special care even in the winterless north: her monstera adansonii. "Mine always drop leaves every winter. All the bottom leaves go yellow and fall off. They really don't like the drop in temperature."

houseplant
Plant lover Kate Hickey has to give her monstera adansonii extra care in winter. (Getty Images/iStockphoto)

Most artificial heat sources that warm up our homes also dry out the air. Many indoor plants can handle lower humidity, but they still prefer at least 50 per cent.

A heated home in winter can drop down below 30 per cent humidity ¨C unpleasant for plants and people.

Plants show signs like brown, dry, crispy leaf tips and leaf edges when humidity drops too low. Some plants are less tolerant of low humidity: Calathea, maranta, peperomia, stromanthe, orchids and ferns are some of the best-known.

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Humidifiers are a great winter solution. (Misting however, is not. Misting only raises humidity a little and for a short time, and in winter also increases the risk of rot.) Like their name suggests, small-area humidifiers raise humidity in a small part of a room, making them ideal when you don't want to raise the humidity anywhere else. I have cordless ones so my plugs are available for grow lights.

Get a hygrometer first to check current humidity levels. If you routinely get readings below 50 per cent or have fussier, higher-humidity lovers, then consider a humidifier.

A pebble tray can help if humidity's not too much below that 50 per cent mark. And just grouping your plants together also increases humidity slightly.

This story originally appeared on Stuff and was republished with permission. Read the original here.

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