x Abu Dhabi, UAE Thursday 20 July 2017

The right pot for your plant requires function and form

The health of your plants depends on what your containers are made of and where you place them.

Pots made from porous materials such as terracotta allow water to evaporate, which can cool plant's roots in summer. iStockphoto.com
Pots made from porous materials such as terracotta allow water to evaporate, which can cool plant's roots in summer. iStockphoto.com

The view from my apartment is as instructive as it is sobering, and the scene is typical of the UAE. Below me, an urban plaza has been built over an underground car park and on top of this giant floating deck, enormous raised planters have been arranged in a grid that complements the intricate paving pattern beneath.

Each planter doubles as a seat, has sophisticated, built-in lighting and was no doubt intended to hold a tree that would one day help to cool and shade the pedestrians who would congregate in the square. I do not know if the planters ever received their trees, but 37 out of 40 stand empty, acting only as enormous litter trays for the many stray cats that patrol the precinct.

As far as I can tell, the planters were never fitted with the built-in irrigation system or drainage holes that would have allowed any planting to survive, and the three that are in use are green only because local shopkeepers keep them that way.

The example is extreme, but the lessons are as valid for the private gardener as they are for the urban designer: when it comes to successful container gardening, forward planning, appropriate plant selection and careful maintenance are essential, whatever the scale of your plot.

Visit any nursery, garden centre or home store and you'll get a sense of just how many potential planters there are out there, especially when you consider that any container can be used as long as it provides sufficient soil and adequate drainage to support plant health and growth.

I've seen lettuce grown in drainpipes, succulents in sinks and herbs in olive oil tins, so if you're feeling overwhelmed by the options, it's always best to start with the plants themselves and the growing conditions that they'll face, and then choose containers that are best suited to the requirements of both. How quickly will the plant grow? What will its eventual size be? Is weight a key consideration? It certainly will be if you need to move your pots around, since a large or unwieldy container can become unmanageable once it's filled with compost, plants and irrigation water.

Similarly, if your roof garden or balcony is subject to high winds, you might need to choose a heavier container or even add ballast to lightweight ones to prevent your plants from toppling over. Will your containers be exposed to the hot midday sun or will they be in full sun all day?

Pots will always dry out faster than the soil in your garden, but certain exposures will exacerbate the situation. If you are planting in full sun, you will probably want a pot made from material that is not porous. Terracotta dries out very quickly, while synthetic resin pots stay cooler and retain moisture for longer. Considering each of these factors at the outset will help you select the right container for the right spot.

Traditionally, plants require repotting into successively larger pot sizes as they grow, not only to ensure that they look as if they are in proportion, but also to prevent them from the waterlogging that can result from a larger body of overwatered compost collecting around a much smaller root ball.

This is less of a concern in the UAE, where containers dry out more quickly and gardeners are advised to use water retentive additives to increase the water-bearing capacity of their soils. However, in circumstances where your pot is considerably larger than the plants you want to use in it, consider using a lightweight fill material such as polystyrene or bark mulch to pack out the main body of your container. You will then only have to use as much compost as is required to create an appropriately sized root zone in which the plants can grow.

Your choice of materials may also play a key role in the ultimate performance of your containers. Plastic pots may be cheap, light and versatile, but even expensive ones can soon become brittle when exposed to excessive heat and sunlight. Pots made from porous materials such as terracotta allow water to evaporate, which can have a cooling effect on a plant's root zone in summer. They also reduce the risk of overwatering and waterlogging because water can escape through the entire surface of the container and not just through drainage holes in its base.

Glazed pots tend to be more durable. They are fired at higher temperatures in the kiln during their manufacture, and they retain water more efficiently than their unglazed counterparts do, but this is not always a blessing because there is an increased risk of waterlogging.

The root zone of plants in glazed containers also gets considerably hotter than it would in an unglazed pot, a problem that is even worse in metal containers, which also run the risk of rust, resulting from the pot's repeated contact with water. Stainless steel and galvanised planters can look smart in an interior, but are probably best avoided for external planting schemes in the UAE.

No matter what type of container you use, make sure there is adequate drainage. Most shop-bought containers will come pre-drilled. If not, or if you are recycling, you will need to drill holes in the bottom.

Finally, before you spend money on expensive containers, make a realistic assessment of your lifestyle, the kind of garden you want, and the amount of time you have to spend in it. Do you travel a lot? If so, self-watering containers are available, particularly for houseplants. These pots contain a reservoir that sits below the planting zone, allowing plants to wick up moisture by the roots.

For outdoor plants and gardens with a lot of containers, however, an automatic drip irrigation system is essential if you want your container garden to thrive throughout the summer. Not only will the system keep your plants well watered, but it should also prevent overwatering, a common tendency among gardeners who use traditional watering cans and hosepipes.

Ask Nick

My husband recently bought me a beautiful orchid covered in blooms but within two weeks they had all wilted, leaving a stem and little else. Was this the plant's fault or mine?

This is a common problem with orchids bought as gifts. Rather than assigning blame to yourself or the plant, I would like to know what advice your husband was given when he made the purchase.

When properly looked after, orchids can be excellent gifts because they flower for such a long time, but when left to stand in water or placed in a draft, they will soon display the symptoms you describe. Orchids, particularly of the Phalaenopsis variety, should be allowed to drain thoroughly after watering and before they are returned to the cachepot or container in which they are displayed.