You’ve kept some plants alive for several months now. Feeling more confident, you bought up big at a recent plant sale. The next challenge is to keep the growing indoor garden happy and healthy.
If you’ve been watching your plants over time, you’ve probably realised they aren’t static; new leaves appear, plants droop if ignored, and the leaves might even change colour.
Like a new parent trying to understand the cries of a newborn, you need to learn to interpret the signs plants give to understand what your plant is experiencing.
Here are few common symptoms and what they may mean:
- Wilting leaves
- Plant/soil not holding water
- Yellowing leaves
- Roots at the surface or coming through drainage holes
- Tips/edges of leaves turning brown
- Flower buds form then drop off before opening, or shrivel soon after opening
- Brown, burnt-looking spots on the top of leaves
- Dropping leaves
- Black dots on leaves, or brown marks with a yellow ring
- Changing leaf colour
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We’ll start with a common but confusing one. If your plant’s leaves are drooping down, you first need to check how dry the soil is to get a bit more information; stick in a finger to the first knuckle to test it. If the soil is dry, the solution is simple — your plant needs water. However, if the soil is still wet, then your plant may have root rot, which is a fungal infection of the roots caused by overwatering.10 mistakes new gardeners makeGardening Australia’s Tino Carnevale talks us through the common mistakes new gardeners make.Read more
Other symptoms include yellowing leaves, sudden dieback of part of the plant (or all of it!), and the plant becoming loose in the soil.
To check, remove the plant from the pot and look at the roots — they should be white or light brown. If they’re falling apart when you touch them, are soggy or brittle and are going dark brown, these are signs of rot.
Wash off the and trim off the affected parts; you’ll also need to trim off some leaves to keep it in balance.
If enough roots remain, dip the roots in a fungicide — such as a 3 per cent hydrogen peroxide solution — then repot it, using a clean pot and fresh potting mix. Water the plant in well, but then leave it alone until the top of the soil is dry when tested with your finger. Wash and disinfect the old pot before using it again.
If the plant’s roots are OK, it could be suffering from low humidity; see below for solutions.
Plant/soil not holding water
To check, knock the plant gently out of its pot and have a look; if its roots are tightly packed (called ‘root-bound’ or ‘pot-bound’), you know the plant needs to be potted up to a bigger pot.
If there’s still lots of potting mix left, it may now be repelling water — hydrophobic — which happens when potting mix or sandy soils are dry for a long time. The giveaway sign is water beading on top of the potting mix instead of soaking in. To fix this, soak the pot in a bucket of water or very weak solution of seaweed extract.
You can also try watering it with a solution of wetting agent, which reduces the surface tension of the water and allows it to penetrate the mix, but be aware most wetting agents aren’t classed as organic. You can make your own mix using agar agar; add one sachet to 5 litres of water.
Older leaves may yellow and fall off as part of a natural ageing process but if it’s happening too much — or to younger leaves — you know you have a problem.
This can be caused by too much sun so, if you think that applies, try moving your plant to a shadier area. Also check your plant isn’t in a cold draught from an open window, door or air-con unit.
Alternatively, yellowing can be caused by either over- or under-watering, so check for that, too.
Roots at surface of soil or coming through drainage holes
The chances are this plant is root-bound and so it will need a larger pot.
Gently remove it from its pot to check the roots. If they’ve started forming circles at the bottom of the pot or there are more roots that soil down the side of the pot, it needs a new home.
Tips/edges of leaves turning brown
If you’ve recently fertilised your plant, this could be a sign you’ve applied too much.
It can also be caused by softened water, which is often high in sodium or potassium.
Another cause is dry air. Many indoor plants are originally from rainforests, so have adapted to high levels of humidity. Without this, they can wither and brown, even when the roots have adequate moisture. Give them a spray every so often and remember to wipe down the leaves with a damp cloth to remove dust.
Plants with hairy leaves, such as African Violets or Rex Begonias, don’t like wet leaves so instead group plants together, or place them on a tray filled with small pebbles and a small amount of water. Another option is to move the plant to a naturally humid area, such as the bathroom or kitchen, if the light and temperatures there will suit your plant.
Flower buds form then drop before opening, or shrivel soon after opening
This could also be caused by low humidity; for solutions, see above.
Brown, burnt-looking spots on the top of leaves
If these marks correspond to where the light hits your plant through a window then you have your culprit — sunburn! Simply move the plant out of direct light and it should be fine.
It’s worth remembering that the sun in late summer and early autumn is still fierce but is lower in the sky in cooler months, so it will reach further into north and west-facing windows, which you might not notice during the week when you’re at work.
Weeping figs (ficus) and Bougainvillea have a habit of dropping leaves when they are moved and feeling stressed — usually they settle down to the new conditions.
But a more common cause is cold air or overwatering; other signs of overwatering include brown or yellowing patches on the leaves, dying leaf tips and, of course, wet soil.
Black dots on leaves, or brown marks with a yellow ring
Various fungal and bacterial diseases can cause this, and it spreads rapidly between plants when they are overcrowded.
Pick off infected leaves and put them in the bin, not the compost.
Mulch the surface with light stones to avoid fungal spores in the potting mix splashing on to new leaves, and ensure the plant has good airflow (not a full-on draught, just a gentle flow), with space between plants. Also avoid getting water on the leaves.
Changing leaf colour
If none of the above applies and your plant is generally healthy but just looking a bit pale and unwell, it could be experiencing a lack of nutrients. Apply a weak solution of liquid fertiliser for a quick boost.
In winter this may be enough, but in the warmer growing season you could follow up with a pinch or two of slow-release plant food, but don’t overdo it — twice a year is enough, and check the packaging for application rates.
Also keep an eye on light levels — plants that suddenly look a lot more lanky and “leggy” can be reaching out for more light, and this can make leaves change colour, too.