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A scientist’s guide to life: 8 tips for growing indoor plants

Stuck at home and cultivating a houseplant habit? Botanist Alastair Culham explains how to keep them happy, healthy and alive.

1

Give your plants enough light

Light is the most important environmental factor to keep houseplants healthy. They need it for photosynthesis. If you’ve got decent light levels, they will photosynthesise more than they respire. If they didn’t, they wouldn’t grow.

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2

Choose the window you put your plants in front of

When the Sun is shining through south-facing windows, you get the most intense light. So that’s where you put your cacti and bromeliads.

North-facing windows rarely get direct sunlight, so this is where you put plants intolerant of bright light, so things like maidenhair fern.

East- and west-facing windows get intermediate light levels, so the epipremnums and tradescantia do well.

3

LED lights help plants grow

Modern cool white LED lights give off a much more balanced daylight light spectrum than old filament bulbs. So a plant that’s directly under an LED is going to get a useful quantity of additional photosynthetic light.

Need to know…

  1. The two things plants need are light and water.
  2. Free phone apps, like Lux Light Meter, can measure light to help you place plants correctly.
  3. Do you neglect plants? Cacti and spider plants will forgive you.


4

Give your houseplant enough water

If you drought stress a plant, its stomata, the tiny slits on the surface of the leaves, close so it doesn’t lose water. If the stomata are closed, it can’t photosynthesise because carbon dioxide can’t get in and oxygen can’t get out. So getting the watering right is important.

Water the compost thoroughly, then let it dry out to the point where the top two or three centimetres are dry to the finger. Then it’s time to water most plants again.

5

Give your indoor plants a nutrient boost

Most composts used for growing houseplants will have had their nutrients leached out by watering within six to eight weeks.

Through the summer, when there’s plenty of light and reasonable warmth, I dilute liquid fertiliser down to about one-tenth of the recommended strength and use that in my weekly watering.

6

Give your plants a fresh start

If your plant is looking unhappy, repot it and give it some fresh soil.

Houseplant compost is not a living soil. You’ve not got earthworms going through it to break it up. Repotting is about restoring the soil structure. The more compact the soil is, the harder it is for water to get through and the less oxygen gets in, so the less healthy the roots are.

Read more from A scientist’s guide to life:

7

Houseplants keep your home’s air healthy

The biggest contribution houseplants make to the air is increasing the humidity, which is often low in centrally heated houses. There is also strong evidence that plants help with mental wellbeing – and that has a positive impact on your immune system.

8

Choose plants that are hard to kill

Spider plants and tradescantias are particularly robust. Cacti are the perfect plants if you’re a forgetful waterer. Put them on a sunny windowsill and don’t worry.

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Phalaenopsis, the moth orchids, have fleshy leaves and are about as tolerant of drought as most cacti. You just water them when they go a bit limp.