What’s the difference between growing in containers, as opposed to growing in the ground? I’ve already written about how there’s less margin for error with a plant in a pot, the rootball having access only to the nutrients available in the container, and that much more vulnerable to sudden changes in temperature. In this week’s lesson, we were again considering the materials used to construct containers, but this time rather than from a purely aesthetic point of view, we’ve been looking at how, for example, a plastic or metal pot will typically have less thermal insulation than one made of good quality terracotta or stone, and how this should affect how you think about siting different containers.
Just as you need to develop an awareness of different microclimates in your garden when planting in the beds and borders, so too this needs to be factored in when planning displays of containers. Not just things like aspect, the location of frost pockets and wind tunnels, but also the potential for strong gusts to be bounced off walls and corners against which pots are placed, potentially causing harm to plant material through air turbulence. And, while you may think that your treasured plants are entirely independent of the ground, being safely ensconced within their pot and with roots nestled into your choice of an ideal growing medium, it turns out that the hard surfaces on which the containers are standing can still have a bearing on how well (or not) the plant thrives. As an example, and rather like an inverted version of the storage heater in my old Muswell Hill bedsit, a dark-coloured ground surface will absorb heat during the day, and slowly radiate the warmth back out at night. I remember this arrangement was pretty hopeless for me, as it meant the bedsit was toasty during the day when I was out at work, and freezing during the evening and night, but careful attention to the needs of your plants should mean that you can take better advantage of the principle.
Practical matters covered this week also included arranging containers in groups, watering and drainage, including the thorny issue of crocks, and the desirable properties of a good compost. Already having packed quite a lot to pack into one week, Harriet ended the tutorial with a consideration of what to look for when selecting plants for your containers, with criteria including foliage, flower and form, as well as texture and habit, and seasons of interest. Much to remember, and to help it sink in, this week’s assignment asked us to choose four perennials or shrubs which we thought would earn their keep in a container display.
Here are my choices.
Perhaps the least fancy Sarcococca, the Christmas box is nonetheless a plant I wouldn’t be without, growing it both in the ground and in containers. An evergreen shrub with a potential to grow over a metre in height after many years, I treasure it for its deep glossy, spear-shaped leaves, and the clusters of black berries. But mostly for the rich, heady, vanilla fragrance of its tiny white flowers in the depths of winter, filling the air with a delicious, warming scent at the most miserable time of year. During the spring and summer months, it lurks within the groups of containers, overshadowed by more flamboyant flowers and foliage, but once the tender things have been put to bed, it begins to come to the fore.
|Close-up of Sarcococca confusa. Sadly not scratch-and-sniff.|
Euphorbia characias subsp. wulfenii
This evergreen subshrub might not be the rarest of specimens, but it certainly earns its place in many different settings. Growing to 1.5m in height, and often rather larger around, the most striking feature for me is the colour – grey-blue foliage, topped with huge acid green flower heads in spring which persist for months. It’s not known for its fragrance, but having worked around it in several locations, I can confidently announce that it gives off a pronounced smell which might be described as bitterly earthy, or woody, but which reminds me of nothing so much as coffee grounds.
|Euphorbia characias subsp. wulfenii in flower. Less yellow, more blue in real life.|
The most tender of my selections, practically herbaceous in my part of the UK, but growing as an evergreen subshrub in climates more akin to its native antipodes, where it has become something of a weed. Here, we love it for its large, pleated glaucous foliage with deeply serrated edges. I was once told by the head gardener of one of our major gardens that it wouldn’t flower in the south east of England, but mine decided to contradict this pronouncement, producing a massive maroon flower spike that November. Just before the frost and the wind reduced the entire thing to black mush.
|The leaves of Melianthus major. Remember, not all peanut-scented things are edible.|
I have heard this glamorous relative of ivy sneeringly classified as a ‘carpark plant’. But, as every plant so labelled is an utterly reliable, unfussy, robust and attractive affair presenting year-round interest, I don’t see it as anything to be sniffy about, and I can’t get enough of its large, glossy palmate leaves. Even better, in summer, older plants flower with the most eerie-looking white umbels. A statuesque presence, in the ground it will happily grow to eight feet in both height and circumference, although in a container it will assume more modest proportions. Happy in shade, dry or damp, it will provide a luxuriant, tropical backdrop to any planting all year round.
|Glossy palmate leaves of Fatsia japonica.|
Do have a look at the My Garden School website, which is still running its Back to School campaign for 15% off all £145.00 4 week online courses in October. (Course start dates: Wednesday 7 October 2015). Click here and remember to use the code MGSBTS at the checkout for the discount.