The Queensland Garden Expo, which is held each July in Nambour, features the usual mouth-watering plant stalls and a busy programme of expert talks. I planned ahead and made sure I was in the right place at the right time to catch fern grower Peter Heaton give his tips for looking after ferns and other indoor plants. The room was packed, and when pushed most of us confessed to being serial killers of indoor plants.
When the victim is an indoor plant, the number one cause of death is too much water. The number two cause of death is not enough water. The twin perils of under and over-watering force many indoor plant lovers toward plants that can safely be watered about as often as baristas get a beard trim– sanseveria (mother-in-law’s tongue), bromeliads, aspidistra. As lovely and tolerant of neglect as these plants are, they look even better when lovingly tended, and when accompanied by other less hardy plants.
Heaton was understanding. The difficulty with watering indoor plants, he explained, is that there are too many variables. How much water a plant needs depends on its size; the size of the pot it’s in; the composition of the potting mix; the airflow; the temperature and the humidity.
Because that’s an algorithm worthy of Fermat, Heaton recommends putting plants in pots on a saucer. Water from the top of the pot til there is water in the saucer and don’t water again until the saucer is dry. The plant roots will take up water from the saucer as needed. If it takes more than a week for the saucer to dry out, it’s too big for the size of the pot, and root rot is a risk. Scale back the saucer.
Fill the saucer with dark gravel. This disguises the weak tea colour of water leached through the potting mix. Evaporation from the pebble-filled saucer will supply all the humidity needed to keep plants happy, including ferns. Misting is not just unnecessary, says Heaton, but a bad idea, as damp foliage is a good environment for the growth of fungus.
So that’s the watering sorted. The other issue is feeding. Heaton says we are mistaken in thinking of our potted plants as mini gardens. Better to consider them hydroponic systems, with the pot there just to hold them up. Which means you need to not only water but to feed. Heaton advocates a not-much-often regime. Add fertiliser to the watering can every time you water, at one-quarter strength of the recommended rate, alternating an all-purpose soluble food such as Thrive or Aquasol with a seaweed solution like Seasol.
Every year refresh the potting mix by taking the plant out of its pot, composting the old mix and repotting into fresh, high-quality mix, with a sprinkle of slow-release fertiliser at the bottom of the root ball and just under the surface of the mix. Add an occasional spray with the hose outdoors to rinse off dust for a total care regime that Heaton promises results in stress-free, thriving indoor plants.