Growing Indoor Plants Successfully

Photo © Bulleen Art & Garden

The thing to remember is all ‘indoor plants’ evolved to grow outdoors, and we are asking them to adapt to an alien, often airconditioned or heated environment. This can be done very successfully if you understand your plant’s requirements. In addition, most will benefit from an extended spell outdoors, commonly during the warmer months. This will freshen them up and keep them looking good. Ideally put them in a shady spot to acclimatize to their outside holiday, and after a month they can return thoroughly rejuvenated to their indoor life.

This is at the top of the list because more indoor plants die from overwatering than any other single factor. Nothing beats either lifting the pot (light pots are dry, heavy pots are wet) or sticking your finger into the potting mix to see how dry it is. There are several things to keep in mind:

• Large pots dry out more slowly than small ones and will generally need less frequent watering
• Actively growing plants use more water, conversely plants in a dormant phase use less. The dormant phase is their ‘rest phase’ and plants can be allowed to get significantly drier than in their growth phase. The dormant phase if often in winter, but not always.
• When you water, water thoroughly, making sure that all the potting mix gets wet and ensuring water drains out the bottom.
• It is ESSENTIAL that pots are not sitting in water. Either tip out water from saucers or raise the pot on feet or pebbles and allow water to pool below. This has the added advantage of increasing humidity, often beneficial to indoor plants.
• In winter, try to water with tepid or room temperature water.
• Consider giving you plants an occasional trip to the shower to give a chance to wash off dust, raise their humidity levels and generally have a freshen up.
• Indoor plants can have wildly different watering requirements – get to know the individual requirements of your plants.

In Melbourne the light that comes through a window can vary enormously depending on the season, what may be a perfectly suitable light level in the cooler months may scorch a plant over summer. There are few indoor plants that can cope with direct summer sun coming in through a window. Move before they get scorched to avoid unsightly damage to your plants.

Choose a plant that suits the position, it is frustrating to try and grow a plant requiring bright light in a low light conditions, it will never thrive, will almost inevitably become prone to insect/fungal problems and end up a major disappointment. Whereas an indoor plant in the appropriate conditions will thrive and give years of enjoyment.

A handy tip is to regularly spin your plants a quarter turn, this helps prevent them leaning into the light and promotes even growth.

Temperature and Humidity
Both heating and air-conditioning reduce humidity. Keep plants away from ducts and outlets. Ideally group indoor plants together as this helps create islands of humidity. Regular misting or a room humidifier helps, as does putting pots on feet or pebbles to ensure free drainage and allowing water to collect underneath.

A sign that humidity is too low is dry crisp edges on the leaves.

All potting mixes run out of fertilizer after a few months and supplementary fertilizing is required. The easiest way is to use a slow release fertilizer at the beginning of the growth period – commonly, but not always, at the start of spring. You can also use liquid fertilizer, but these do not last long and need to be used regularly over the growth period.

Your pot plant should be flushed annually. This process flushes away the salts that build up in the potting mix. To flush the pot, water several times in succession, soaking the pot each time until water runs out of the bottom.

Cut any dead or damaged leaves or fronds away, pruning as close as possible to the base of the plant.

If you want to polish or gloss the leaves, only do this with suitable plants, like Ficus elastica, Philodendrons, Monstera, aspidistras etc. Never ferns or palms. If using an oil, only ever polish one side of the leaf.

If the plant is getting to large, prune back as necessary. Most plants respond well.

The only time you ever use garden soil is when repotting water plants, for all other repotting, always use potting mix. Garden soil in a pot settles and consolidates, aeration and drainage are reduced and plants fail. Potting mix is formulated to retain its structure, allowing good aeration and drainage even after years.

Repot when plants are actively growing. Avoid hot and or windy days as this tend to rapidly dry everything out. Try to have everything ready before you start, and water the plant to be repotted the day before. Choose a pot only one size up from the existing pot. Roots will rapidly take moisture from the potting mix, if the root-ball is surrounded by a large amount of fresh potting mix, this will stay wet increasing the likelihood of root disease.
Place a few centimetres of potting mix in the base of the new pot – you want the final level of potting mix to be the same in the new pot as it was in the old pot. Carefully remove the plant from its old pot and examine the roots. This is important. If the roots are in good condition, with no girdling (wrapping around) or significant kinks, then it can go directly into the new pot. However, if there is girdling or kinking, or just a solid potbound mass, then these roots need to be loosened away from the rootball and removed (cut away). If a lot of root material is cut away, then remove a proportion of top growth to compensate. This allows the smaller root-mass to serve a smaller leaf load and the plant will recover quickly and surge ahead without a setback.

Site the plant in the new pot so the centre of the plant is roughly in the centre of the pot, if the plant was unevenly centred or tilted at an angle previously – this is your opportunity to correct that. Then pour potting mix around the sides, tamping down. Water well to settle the potting mix and remove any air pockets. You can water in with a very weak seaweed solution or plant starter solution, but it is not essential. Leave in a shady spot for a few days and it can then go back inside. Do not fertilise for a month after repotting.

Be vigilant looking for pests, most commonly mealy bugs, but also mites, aphids and scale. Plants attacked by pests are often under stress, treat the pest, and try to solve the reason why the plant was stressed in the first place. A holiday outside can also help.

Avoid using oil sprays on ferns – they generally react poorly.

Root rots: When plants are overwatered or poorly drained, the roots will rot away, resulting in an inability to take up water and the plant starts to droop. This often leads to a misdiagnosis of the plant needing more water, and the situation rapidly deteriorates – end result, a dead plant. If you catch the problem early, you can trim away any dead root material, repot into as small a pot as possible and trim away some of the foliage to compensate for loss of root mass. Put in a shady spot outside and cross your fingers. If you want to reuse the old pot – you will need to disinfect it with a bleach solution. Wash out pot then use a 1:100 dilution and rinse thoroughly.

Fertiliser burn: Symptoms can look similar to those for low humidity – leaf tips and edges will scorch or crisp. With indoor plants, if you are unsure how much fertiliser to apply – go for less rather than more. If they look hungry you can always add a little more later.