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Overwintering houseplants

It’s possible to keep your indoor jungle lush and healthy through the winter season, but it takes a few adjustments.

STORY: 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 – 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?

Kellie Vince – known as @thelittleplantfairy to her 25,000 followers on Instagram – 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 Whangārei home 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.

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, 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.

Watering 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% of water roots take-up stays in the plant, with as much as 99% 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.

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 Whangārei 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 Kate’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.”

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 Kellie’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.”

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.

The one tool Kellie 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.”

Let there be light

Many of the plants kept indoors here in New Zealand grow wild in their native homes. The many varieties of philodendrons, for example, are native to the tropical Americas, a region that includes the Amazon rainforest in Brazil, where the average temperature remains around 25C all year round, with about 12 hours of canopy-filtered sunshine every day, and humidity at more than 70%.

This is why most indoor plants don’t go dormant over winter, and why light and temperature are the biggest challenges for them during a typical New Zealand winter.

With so many different types of grow lights available now, it’s much easier to artificially boost light levels over winter. Grow lights mean there’s no “bad place” for plants anymore. Linh Tong’s main plant shelf in her Wellington home gets late afternoon sun in summer. Come winter, she supplements what little natural light they get by adding LED grow lights for the plants she can’t move. “I keep an eye on changes in the direction and intensity of the sun in winter and shuffle some of my plants based on that. I find some, like my ficus, philodendron and monstera, can tolerate direct sun in winter because it’s less intense, and they keep growing right through the season.”

A low-tech or no-tech approach is simply choosing plants tolerant of lower light levels. Leaf colour can be a good clue with darker green-leafed varieties coping better with lower light levels temporarily. Keep in mind low light doesn’t mean no light: If you can’t read easily with the lights off, it’s too dark for your plants.

It’s tempting to shift plants closer to windows for more light over winter, but beware of cold windowsills at night.

Wipe for winter

Clean, clear windows make the most of the light you do get. A plant’s leaves are like solar panels so give their leaves a good clean too. The layer of dust they accumulate over spring and summer can get in the way of photosynthesis in the lower light of winter.

As impressive as a glossy leaf looks, I stay away from most

commercial leaf shine products. Many are comedogenic, leaving a waxy layer behind that can block stomata. There are some commercial brands such as Plant Runner that make organic, neem oil-based leaf shines that are noncomedogenic. Plain water can do the job too. I often use makeup wipes for my little-leafed houseplants. Biggerleafed ficus and peace lilies get washed down with warm water in the shower. African violets, and other furry and spiky leafed plants get “dry cleaned” with a small, soft brush.

Some plants like orchids and begonias are more prone to leaf and stem rot if water is left sitting on leaves or in crevices, especially in winter when leaves take longer to dry. Rather than spray them directly, I apply leaf cleaner to a microfibre cloth or cotton pad and gently wipe them down.

For water spotting that won’t budge, my home remedy is a lemon: Lemon juice helps dissolve water spots. I use one tablespoon of lemon juice mixed with two cups of water.

Warm, but not dry

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

It’s tempting to shift plants closer to windows for more light over winter, but beware of cold windowsills at night.

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.

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 Kate’s Whāngarei 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.”

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%.

A heated home in winter can drop down below 30% humidity – 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.

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% or have fussier, higher-humidity lovers, then consider a humidifier. A pebble tray can help if humidity’s not too much below that 50% mark. And just grouping your plants together also increases humidity slightly.

Can I repot in winter?

This one is a little controversial. You’ll often be told to never repot in winter. Not bad advice for beginners, as repotting for plants is like major surgery for us, and giving plants the conditions needed for a fast recovery, with no complications, is easier in warmer months.

I think with the help of a heat mat, higher humidity and a grow light, repotting can be done even in cooler months. My approach is to look at the plant’s health – if it’s badly in need of repotting, it gets what it needs, even in winter.

But, what works for one hobbyist, might be a disaster for another. The biggest factor is not the plant, but the conditions we give it. Repotting at any time of year is not without risk. Kate Hickey takes a slightly different approach in winter but will repot any time of year. “If you know the risks then by all means go ahead! I do. I find repotting a day

or so after watering the plant is the best time, when it’s hydrated and happy. I prefer to keep the root ball intact if possible and in winter, I don’t water it straight away after repotting like I would in summer.”

Should I stop propagating?

The joys of watching a cutting root and grow is hard to beat. Linh continues to propagate in her Wellington home all year round also. “I think winter is the best time. I keep my cuttings in a controlled environment that provides optimal conditions for cuttings to root and grow, in a propagation box on a heat mat, under a grow light,” she says. “Come spring, it’s also less of a shock to baby plants when they are ready to leave the propagation box after winter. I prefer to use pumice or moss in winter as it’s easy to see when the medium is dry and needs water. This helps me avoid overwatering which can lead to roots or the cutting rotting.”

Linh finds airflow extra important in winter and uses propagation boxes which have adjustable ventilation in the lid to avoid mould and rot.

In Whangārei, Kate tends not to propagate in winter. “If I do, they usually go in my grow tent or propbox with grow lights. Keeping propagations warm is key over winter.”

To fertilise or not to fertilise?

There are three general approaches: No fertiliser at all; feeding less often; and feeding as normal. In Taranaki, Kellie takes the first approach. “I cease fertilising around June and restart once the first warm spring days arrive.”

Kate in Whāngarei takes the second approach, feeding “every second or third time I water and use the weakest dilution rate.”

I prefer to feed my houseplants lightly, every time I water, all year round, often called the weakly-weekly method (although it’s not literally weekly). This approach works best with a complete and balanced fertiliser that’s lower in salt.

Give your houseplants the conditions they prefer, and as they do in the wild, they will happily grow through winter, albeit a little slower indoors in a typical New Zealand winter. As they go through water slower in winter, you’ll naturally fertilise less anyway as you’ll be watering less often.

The good news, if you don’t fertilise in winter (or at all), is that many essential minerals are mobile, meaning your plant can move them around itself to survive. If you notice a lot yellowing older leaves during times of growth, that can be a sign you need to feed. Not feeding in winter is one reason yellow leaves are so common in spring.

I have come to love the break winter gives me from the need to keep everyone hydrated in summer. Most of my jungle happily continue growing right through winter, so I still get the enjoyment of watching new leaves unfurl.

ROSES

en-nz

2023-06-01T07:00:00.0000000Z

2023-06-01T07:00:00.0000000Z

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