Does your houseplant look forlorn, with its leaves yellowing and drooping?

It may be that you are overwatering it, which is among the most common mistakes made by houseplant lovers around the world.

Help is at hand from Joe Bagley, aka The Houseplant Doctor. Bagley says some plants are more susceptible to overwatering than others, such as those with thick stems, including the yucca.

Others need more watering than others, such as pots containing multiple plants, which will be competing for moisture.

He offers some pointers as to where indoor plant lovers are going wrong.

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What are the symptoms of overwatering?

“Overwatering symptoms are pretty much identical to underwatering symptoms, so you still get the leaf curling, and potentially the oldest leaves will turn yellow or brown quite quickly.

“If the odd leaf turns yellow or brown or drops off once or twice a week but the plant’s still growing, that’s fine, but if it’s a rapid change of appearance, that could be something wrong with the soil.”

Look at your soil, he suggests. If it’s very dry and crumbly and doesn’t smell of anything, the chances are the plant is fine.

“If the room is warmer than 18C to 20C is best – the plant is very unlikely to have root rot,” he observes. “However, if there are issues of overwatering and root rot, the soil will be very clumpy and will smell very earthy, as if you’re in a field. It will also look very wet, very heavy.”

How can you tell if your houseplant has root rot?

If you’ve overwatered, take the plant out of the pot and before touching the roots or the soil, scan the outer edge of the root ball. Most houseplants will have a bright coloured root system which is cream or greyish in colour. The only exceptions are ferns and dragon trees, which have darker roots, he explains.

“Pinch one of the roots and very gently pull it. If it stays within the soil and with the plant, and it doesn’t come off easily, that is not root rot. It’s more likely that you’ve underwatered it.

“If the roots smell and look brown and shiny and if you pinch one it’s quite mushy and you can easily pull the root off, then that’s overwatering and that’s root rot.”

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How can you help the plant recover?

Move the soil where the dead roots are and if you see any healthy roots, nip the dead tips off by about a third then have a look at how much root system is left, he suggests.

“If less than 20% of the root system is healthy, repot it into a smaller pot, as you want the rootball to be snug. If it’s only a few dead roots, pull them off or use scissors if it’s easier and repot the plant back into the same pot, making sure there’s a little bit of soil where you’ve removed some of the pre-existing soil.

“Then, just increase the light and water the same amount, but less often, once every two weeks or suchlike, with the same amount of water, so it drains through the drainage holes below.”

Key tips for watering

“For houseplants – it doesn’t matter if it’s a cactus, a succulent, bonsai, peace lily, a tropical plant or a desert dweller – the best thing to do is give it a flush of water all at once, so drenches between droughts, and let the soil almost dry out in between waters.

“If they are not in direct sun and the house temperature is 18C to 22C, then allow most of the soil to dry out and flush the plant with lukewarm water, so you don’t shock the roots.

“Sometimes it’s best to keep a little bit of soil moisture in the pot if the room is warmer than 23C or it’s next to a radiator or in sunlight. Those three elements will dehydrate the soil too quickly and can cause underwatering issues.

“The only two exceptions are carnivorous plants, which need to be kept in water all the time, and orchids.

“With orchids, you only water them when the roots turn silver in the pot. While the roots in the pot are green, don’t water them.”

When is the soil dry enough for watering?

The best way is to feel the weight of it in its plastic pot and see how light it feels, he says.

Give it a drench once a week, or maybe even two depending on the temperature of your room.

“The only time you really need to water the plant is when you pick up the pot and the stem and the leaves feel heavier than the pot itself, so the plant feels a little bit top heavy and the soil is quite lightweight,” he says.

Give it a good water and after a couple of minutes of draining the excess water away, it should feel quite heavy, he explains.

Ways to water

Generally speaking, from the top downwards is always better, because when you water a plant from the top down, the water will disperse better through the potting mix, he advises.

You can submerge plants from the bottom, but the lower half of the potting mix can become saturated and a little too wet for the plant, he warns.

“Submerging is really only great for plants in a 15cm pot or smaller, because the smaller the soil profile, the less of a sponge there is to soak up the moisture,” he recommends.

Should you avoid watering the leaves?

“Some plants don’t mind it, others really hate it,” he says. Avoid watering the leaves of streptocarpus, African violets and orchids, he recommends.

“If you are in a warm room near a window, don’t worry too much as the water will evaporate but if the room is cold and more than a metre away from a window, make sure the leaves stay dry.

“You can mist the foliage from time to time but don’t do it too often, especially in colder rooms, because that can cause fungus.”

If you are wanting to get rid of the dust, you may be better of using a damp cloth on the leaves, which will also knock off pests, he advises.