3 ways to avoid root rot in winter

Winter and water can be enemies when it comes to our indoor plants. Even though I've changed my chronic over-watering ways, the risk of root rot never entirely goes away, and winter is when the risk goes WAY up. Here are 3 winter water problems to watch out for, and the 3 easy ways to fix the risks.

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#1 When dry soil does NOT mean it's time to water

One problem in winter is the usual methods of knowing when to water can mislead you. As heaters get turned on and fireplaces lit up, artificial heating dries out the air.

That means it also dries out the surface of our indoor plants. Potting mix can look and feel dry in winter, but hiding under the surface the soil is still wet down by the roots. If you get fooled into watering again too soon, bang, you've accidentally over-watered and root rot comes knocking :(

Do this before you water in winter

The simplest solution even experienced collectors recommend is a water meter. Although different types of meters go about it differently, they all work by telling you what's going on below the surface, deeper than your eye can see or finger can reach. 

For smaller pots I find the colour-changing water meters work best, like the digital Crew Soil Sensor or Sustee Water Meter (if you're an international plant buddy you can get Sustee here from Amazon also). Sustee come in large sizes too, for pots right up to 36cms wide, but you do need one per pot as Sustee are designed to stay put in the pot and slowly change colour as the water dries out, making them probably the easiest method of knowing when to water at a glance. 

The Crew ones can be shifted from pot to pot, so you only need one for your entire jungle. You slide them into each pot, press the sensor, and they light up a different colour on top depending on the moisture level down below.

For larger pots I prefer a manual water meter, like the NZ made GrowProbe or an el-cheapo 3-in-1 water meter (the ones with two metal prongs and a dial on top). However most water meters won't work if you use a very chunky mix, like bark. They may always read dry because the substrate has such big air gaps, or may give you inconsistent readings.


The NZ made GrowProbe water meter. This type goes right down to the bottom of the pot and takes 4 soil samples at different levels. When you pull it out of the pot, you can both see and feel how moist the soil is down at root level.


#2 When humidity kills

How low is too low?

A typical heated house can drop down below 30% humidity in winter. A bit sad for our plants when you consider many come from tropical rainforest habitats in the wild where their dry season is still above 70% humidity! But even humans start to suffer when humidity drops too low, with between 30% and 50% recommended for us. Symptoms such as dry eyes and chapped lips, eczema, allergies and asthma can all be aggravated by too-dry air. Although they may prefer it higher, most houseplants will be fine if you can average above 50% humidity for them.

What are the symptoms of low humidity?

When humidity gets too low for our plants, it can show up as leaf scorch, brown, dry leaf tips and leaf margins, leaves that curl or shrivel, wilting leaves and soft stems that bend. 

What would you do if you notice a plant's leaves wilting, curling, dry and crispy? My instinct would be to water, and fast. But when it's caused by low humidity, not the plant's roots needing water, watering could kill. That's why low humidity increases the risk of root rot when all your plants really needed is higher humidity.

3 ways to fix low humidity (and the 1 to avoid in winter)

The good news is a small-area humidifier can help fix that for your plants (humidifiers help us too, but plant humidifiers tend to be a bit small to raise humidity in an entire room let alone your entire house). But before you get all worried and run out and buy a humidifier, get your plants a hygrometer first.

Hygrometers start around $10 and will tell you what your humidity level is on the fly. Monitor the readings for a few days, at different times of day, and if it's routinely dropping below 50% humidity, then yes, a humidifier is a great idea. But if it's staying above 50% humidity (unless you know your types of plants don't tolerate low humidity), try a pebble tray first and keep monitoring.

Even grouping your plants together will help raise humidity a little (although leaves touching can increase the risk of pests from one plant setting up home next door). If you can average above 50% humidity through winter, most indoor plants will be okay, even those that do come from high-humidity habitats in the wild. After all, the very reason a lot of common houseplants are so well suited to living indoors with us, is because they can grow in the same conditions we live comfortably in.

However, there absolutely are fussier jungle members (I'm looking at you Calathea), who simply won't tolerate low humidity without suffering. Popping them in a cabinet over winter can help (I have some of mine in a converted Ikea Rudsta wide). But often the easiest (and cheaper), solution is a humidifier. 

Misting gets a big NO from me, especially in winter. Misting only raises humidity for such a short time that it barely benefits plants (unless you plan on misting every hour or so). In winter, misting also increases the risk of leaf and stem rot and fungal diseases taking hold if leaves are wet for too long, especially if the water doesn't fully evaporate by night-time.   

#3 The right soil saves (and the wrong soil kills)

The right potting mix takes SO much watering stress away. If you've got your plants in a mix with the right balance of drainage, air space and water retention, the risk of root rot goes way down. However working out the right balance is not just about the plant, but also about your plant parent style, and the conditions at your place.

I'm a recovered over-waterer. My plant parent style has gone entirely in the other direction. I now under-water to the point of neglect (sorry plants). For my plant's sake, I tend to choose mixes that have medium water retention, a higher level than most home hobbyists might use. 

Also take into account what worked in summer might fail you in winter. The mix your plants came in from the store is often NOT good for them in the average home over winter. Commercially grown plants are typically kept in a controlled environment that's been set up for maximum growth, to quickly get plants big enough to sell. Plants are given the perfect conditions for light, humidity, fertiliser, airflow and more.

A potting mix that has high water retention is ideal in that environment so plants don't dry out too fast and growers can keep up with their high demands for water to fuel that rapid growth. But if a grower used the same more airy, free-draining mixes we do at home, they would be constantly watering to keep up with how fast the substrate dries out without losing plants to drought.

When plants come home, changes in light, temperature, airflow and humidity can all cause plants to go downhill temporarily while they adjust. Hardier plants cope much better but more sensitive plants - especially ones with big patches of variegation - often suffer more, until they adjust to the different conditions. 

Should you repot a new plant before winter?

Personally I now always repot into a really good substrate about a month or so after I get a new plant home, no matter what the time of year. I didn't used to but have learned how much better plants do, and how much easier winter is, with the right potting mix.

For the first month after coming home, they hang out by themselves to make sure no pests came along for the ride. I let plants adjust slowly and try to keep the number of changes to a minimum, especially for weaker or more sensitive plants. Thai Constellation, Ficus Tineke and Manjula Pothos are the three I get asked about the most often because they like to freak you out with the weaker variegated areas of leaves often turning brown, usually 2 to 4 weeks after coming home. Once a new plant has settled in, unless it came in a great potting mix, it gets repotted. I'll happily repot any time of year. With the help of a grow light, heat mat and high humidity to help with recovery, there's no reason not to.

However my plants are spoiled with me having a plant store on-hand. If you don't have all those goodies - and winter at your place gets a bit dark, dry and cold - but you're worried about your soil being okay in winter, you can repot right up to mid-Autumn depending on when those wintery conditions really start to set in. You can also increase light, heat and airflow in winter, which all help plants use up water faster, and soil the dry out faster, reducing the risk of root rot.


I think I included way more than 3 ways to reduce the risk of root rot in winter there, but I hope at least 1 of them helps you (and your plants) this winter. Happy growing - Anna :)

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