You may need:
Houseplant compost
Plastic or terracotta plant pots (with drainage holes)
Outer containers (without drainage holes)
Pea gravel, pieces of slate or other decorative stones or glass pebbles
Slow-release indoor plant food
Corrugated cardboard
Small watering can
Bottle of Fungus Gnat Off
Pesticide spray (preferably organic)

Indoor
plants may seem like fickle things, prone to wilt at a moment’s notice
or be suddenly enveloped by unattractive haze of mystery pests. But
think about it: unlike a plant in a garden, they’re entirely dependent
on you to stay alive – no rain falls in your kitchen, and there are no
hungry ladybirds passing by to devour aphids. Most problems with
houseplants and indoor herbs stem from a few issues: watering too much
or too little, outgrowing a pot, lack of nutrients, and pests.

Is your plant wilting?

Confusingly,
this can be a sign of both under- and overwatering. Most houseplants
like their soil to be just moist to the touch – wait until the surface
is nearly dry before watering again. If dryness isn’t the issue, check
the plant isn’t sitting in water. Many houseplants struggle in the dry
air of modern homes: it helps to group them together, or stand pots on a
shallow tray containing gravel and 1cm or so of water (not enough so it
waterlogs the pot).

Is your plant failing to grow?

Unless
it’s newly bought, your plant could be pot bound. If you can see roots growing
through the holes at the bottom, it’s time to give your plant a
bigger pot, 1-2cm wider on each side. Ease the root ball out of the old
pot and tease out the matted roots. Don’t add crocks or gravel to the
bottom: it’s a myth that this improves drainage. If you are worried
about leaking compost, add a circle of corrugated cardboard inside the
pot base. Add enough new compost (specially formulated houseplant
compost is best) so when you put the plant in the centre, the surface is
the same level in the old pot. Trickle compost down the sides and tamp
down with your fingers until the whole pot is full, then water
thoroughly.

Another
problem could be a lack of nutrients. New compost contains enough
fertiliser for two to three months, but after that you’ll need to feed
regularly during the growing season. Fertilisers come in liquid, tablet
and granule form, but I like EcoCharlie’s Black Caviar organic plant
feed.

Is your plant covered in insects?

How to rescue house plants - aphids and gnats
How to rescue house plants from aphids and gnats. Illustration: Emma McGowan

Aphids
and fungus gnats are the most likely culprits. Aphids are
fast-multiplying sap-sucking insects and can be green, black, yellow or
pink. They are easily removed by gently brushing away with your fingers,
or spraying with an organic pesticide made from fatty acids or plant
and fish oils. Fungus gnats are tiny black flies that hang around
houseplants but it’s their larvae lurking among the roots that do the
damage. A thick layer of mulch at the top of the pot helps, but the best
cure is an organic treatment called Fungus Gnat Off – it’s expensive at
around £20 a pop but it will treat all your plants for ages.

Finally,
it may just be that your houseplant needs a makeover. Conceal ugly
plastic pots within upcycled containers – an old casserole pot filled
with bushy basil, or an old enamel bucket sporting a dragon tree,
perhaps. Cover bare compost by adding a top dressing of stones, shells
or glass pebbles in a colour that complements the pot. Not only will it
look better, it’ll cut down on watering too.

• Jane Perrone is the Guardian’s gardening editor and the author of The Allotment Keeper’s Handbook. She blogs about organic gardening at Horticultural; @janeperrone

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