Forgetfulness and over-watering are a houseplant's greatest enemies. Frequent physical checks will help you better understand the needs of your plants.
Mindfulness and a healthy setting are key to houseplants' vitality
When it comes to caring for houseplants, the difference between what people say and what they actually do can often be quite dramatic.
While we were driving from Abu Dhabi to Dubai recently, a friend asked for horticultural help with some ailing houseplants. Despite not being able to inspect the plants, I asked a long list of questions before hedging my bets and suggesting that the issue might be a matter of over- or under-watering.
It was only when visiting the same friend a week later, however, that the full extent of the problem became clear. Despite assurances that the plants were in good light and were not over-watered, the truth could not have been more different.
They were in a dark room, blasted by an air-conditioning unit and planted directly in cachepots that, lacking any drainage holes, were fast becoming ponds thanks to a relentless regime of weekly irrigation.
Had the plants been human, then the correct diagnosis would have been rickets, frostbite and pneumonia. As it was they were simply chlorotic, singed and almost fatally waterlogged.
Such situations are a common occurrence. Over-watering and forgetfulness are the most common causes of plant loss in the home, despite the fact that watering is the factor that most-obsesses home gardeners.
There are, unfortunately, no quick and easy solutions to this issue as a plant's irrigation requirement depends not only on the species in question but also upon environmental conditions, as well as a number of other factors.
In general, species with thick, waxy, hairy or silver leaves will require less water than those with thin, fine or feathery foliage but, as always, knowledge of a plant's species-specific requirements is essential because some naturally require drier conditions while others will not tolerate dryness or wilting at all.
Unsurprisingly, plants in very dry, hot conditions will require more water than those in a state of high humidity, and those that are actively growing or in flower will need more than those that are dormant. Plants grown in very free-draining compost will require more frequent watering as will those grown in porous pots - unglazed clay pots tend to dry out quicker than plastic or glazed pots - or pots that are too small.
If a plant is in too small a container in proportion to its size or is root-bound, consider transplanting it into a pot that is the next size up but beware making too great a leap. If a pot is used that is too big for a plant's root system it may struggle to use the excess water held by the extra potting medium and suffer from over-watering.
A common piece of advice often given in plant and garden centres is to water once the crust of the planting medium has started to dry. Unfortunately, this method can also lead to over-watering as many houseplant roots are actually found in the bottom two-thirds of the root ball and watering should really only take place once this zone has started to dry.
To establish that this is the case, it's necessary to test the soil deeper inside the pot. For a pot with a diameter of 15cm, stick your index finger about 5cm into the soil (approximately to the second joint) and if the soil feels damp, do not water. Keep repeating the test until the soil is barely moist at this depth and then water again.
Some retailers sell soil moisture meters to do this job for you, however, these are not always reliable as the amount of fertiliser in the soil can influence the reading. If you fertilise heavily, the meters tend to read that the soil is moist even when it is dry.
When it comes to watering houseplants, there really is no substitute for regular, physical checks, as these will also help you to learn the particular foibles of your plants and spot any problems, pests or diseases before they have a chance to take hold.
When you do water, take smaller plants out of their cachepots, and continue until the water runs out of the bottom of the pot. Doing so serves two purposes: firstly, it washes out excess salts that can result from fertiliser residue and secondly, it guarantees that the bottom two-thirds of the pot is receiving the water it needs.
However, unless you are dealing with plant species that enjoy having damp root systems, do not let the plant sit in the water that runs out as this can lead to root rot, salt injury and generally poor plant performance.
To prevent the problem, discard any water that may have collected in your cachepot after each watering, or elevate the base of the plant pot above the level of drainage water.
One way to prevent the pots of larger plants from sitting in accumulated water inside a cachepot is to spread a layer of gravel in the bottom that is deep enough to keep the plant out of the water. Another solution is to use a self-watering container that uses a technique known as subirrigation.
When they are well-maintained, self-watering containers that use subirrigation are capable of removing much of the stress associated with irrigation for both you and your plants. When watering from above, a plant's root ball can experience stress as it veers between drought and flood conditions (especially if you are prone to forgetfulness).
With subirrigation, the plant keeps its own root ball constantly moist by drawing up water from a reservoir in the bottom of the pot using capillary action, like a sponge. A simple watering pipe connects the reservoir with the surface of the pot and this normally has a gauge that tells you when the reservoir needs refilling. If this all sounds too good to be true, it is.
Such containers tend to be ugly and are often of a size that precludes the use of a more attractive cachepot. This ultimately makes houseplant irrigation a matter of aesthetics, something I am happy to leave up to you.
Garden Buy: Patrick Morris Sky Planter
For those of us whose compact kitchens don't have enough surface space to accommodate an indoor herb garden, seek out the award-winning Sky Planter by Patrick Morris, a unique, space-saving hanging pot that can be attached to the wall or ceiling. The obvious question is how does the soil stay in the pot? A ceramic collar fits around the stem of the plant and connects to the planter body with small tabs (a bit like a tea pot lid), plus an additional piece of plastic mesh fits around the stem to keep everything intact. To water your plant, you need to fill the reservoir on top of the pot. The water will seep gradually to the plant roots, minimising water loss through evaporation or drainage. A medium-sized planter will typically hold enough water for up to two weeks in an air-conditioned climate, although you will need to refill more often in warmer temperatures. The small version (9cm diameter) is just the right size for shop-bought herbs, while the bigger size (16.5cm diameter) will accommodate most medium-sized house plants. Sky Planter, Dh145 (small) and Dh348 (medium), plus shipping. www.rocketstgeorge.co.uk
Ask Nick: Seasonal menus
Q: How often should I feed my plants in the summer months?
A: Many species enter a period of dormancy at this time, and it would be a mistake to encourage growth in such species through inappropriate feeding. Excess growth, particularly of young, fleshy stems and leaves will increase the rate at which plants lose moisture and reduce their ability to withstand drought.
Some plants, however, flourish at this time and these will require feeding, as will those showing signs of chlorosis caused by the leaching of nutrients that can result from increased irrigation rates. Apply Sequestrene or iron chelate to chlorotic plants as this occurs and feed active plants as per the instructions on your chosen fertiliser.