I hosted a workshop a few weeks ago now, at Petersham Nurseries, with the title of ‘Stylish late-summer containers. I promised the guests that I would create some notes and have been very tardy I doing so. I hope to remedy this here, jotting down a few of the points we covered, and details of the containers that I went on to plant up after the event, that are placed around the Nurseries now.
I would, generally, have expected to be using some of the stalwart late summer perennials, Rudbeckias, Salvias, Heleniums, Kniphophia and Asters maybe but none were available – the unseasonably hot weather brought them out much earlier and pot-grown plants were not to be had. But along with Crocosmias and Echinacea, and Sedums, Gaura, Russian Sage – Perovskia atriplicifolia, and the long-flowering blue Geraneum Rozanne (shown above together with Salvia Ember’s Wish, sparkling daisies such as Erigeron karvinskianus and the beautifully scented rose Lady Emma Hamilton), these are generally ideal container choices with a long season of flowering and with complimentary rich and warming colours. Some examples in the following gallery.
You can see from the mix here that you can focus on the warm tones of gold, orange and chocolates, highlighting the mix with intense shots of red and blue. Regular deadheading and a good feed will keep these plants going through until the first frosts.
I should also add Dahlias to the mix. Many are larger plants that would prefer the roominess of open ground, or a very large pot, with a rich diet, but there are smaller varieties that will give a succession of blooms from July right through until November. The range of styles, shapes, leaf and flower colour is staggering. Pot up tubers in a protected environment in February or March, moving them outdoors once the last chance of frost has passed, in May most likely, feed and water generously and they should be in flower by July and on through the next four months.
Japanese anemones are similarly superb late summer and autumn flowering colour, though most are suitable only for a larger container. New varieties like Fantasy Cinderella and Fantasy Pocohontas (great names!) might sit in a smaller pot, and once again keep deadheading regularly.
These are ideal also for a shadier spot, whereas most of the ones noted before are definitely sun-lovers.
For more suggestions for shade, there are several articles in this blog covering winter, spring, summer and autumn.
But enough of what I didn’t have and couldn’t use, let me move on to some basics to think about when choosing, planting and placing containers.
Below, one of my favourite grasses, Hakonechloa macra.
Choosing the right pot
It should go without saying that the pot should be large enough for the plants you have in mind! The larger the container, the greater the reservoir of growing medium, compost, fertiliser and water. Your plants will be happier and the work you would need to put in will be correspondingly easier. You don’t want to overwhelm a small specimen in a mass of compost is also true, so it is a balance.
Have an idea how long the planting is going to spend in the pot and consider the stability when potted up. A tall pot with a narrow base and a tall plant might easily topple over. If the plant is going to need a supporting stake, then you will need sufficiently deep compost to accommodate this.
The entrance to Great Dixter
Pot shape is also a factor, particularly if the neck of the container is narrower than the ‘belly’. It will be impossible to take the plant out to repot, without either breaking the pot or damaging the root ball.
The shape of the pot should compliment the shape and style of the planting – there is a balance to be made between the container and the planting.
Dazzling displays at Great Dixter
The choice of materials is vast, with natural terracotta, stone, slate, glazed earthenware, wood, concrete, metal, plastic and resin and improvised containers all available in a wide range of classic, contemporary or quirky design. Keep to one style and one material if you are using more than one planter. But you don’t necessarily have to have exactly the same style – a selection of terracotta pots will have a family resemblance, but if rhythm is wanted, with a repetition of pots in a scheme, it is probably best to stick to the same pot throughout.
Terracotta is porous so may need more watering than glazed earthenware, metal, stone or plastic and resin. Metal containers should be insulated if they are to be placed in a sunny position, as the metal with easily heat up and hot metal will damage the delicate plant roots. Polystyrene sheeting, cardboard or the Sunday newspaper can be used to line the sides of the pot (but not the bottom). Plastic and resin and lighter than many other materials, and where weight is an issue, on a roof terrace or balcony, this might be something to consider. There are some very good choices that can on even close inspection, pass for natural terracotta, lead or stone.
Plants grouped at Great Dixter
Wooden planters have a more limited shelf-life once planted up, and the sides will need to be lined to protect the wood from being in contact with damp earth.
Drainage is essential and your outdoor containers should all have a hole at the bottom, which you can cover with crocks of broken terracotta, to prevent the soil from clogging up the hole. You might also consider putting a fine mesh directly over the hole, as this will prevent vine weevils, a serious pest, from getting into your planter. The adults can shelter under the crocks and set out at night to chomp on your previous plants, and the grubs live in the soil and can decimate your stock. These critters love a container and can do a lot of damage.
In winter, if the pots are standing on a hard surface such as a stone patio or wooden deck, ensure you use pot feet so that it can freely drain. Not so important for the rest of the year, but water can build up in a container and after a frost, will damage pots that are otherwise considered frost-proof. Freezing a large volume of water can cause catastrophic failure.
Compost, fertiliser and watering
For a seasonally changing selection of plants, a multi-purpose compost is generally sufficient. We used a wool compost for the workshop; the wool replaces traditionally used peat for water-holding capacity, and it is enriched with chopped bracken which is a rich source of plant nutrition.
For a permanently planted container, where plants will mature for several years, a loam (soil) based compost should be considered. John Innes #2 or #3 would be my choice. It is seven parts sterilised loam, three parts peat and two parts sharp sand, mixed with fertiliser and a little lime. The numbers refer to the increasing amount of fertiliser in the mix.
Be aware that some plants such as Camellias, Rhododendrons and Azaleas, Pieris – Blueberries too – need a lime-free Ericaceous compost. It is preferable to water with rainwater and to use an ericaceous feed, which will be labelled as such and probably contain iron.
You can blend your potting mix with grit and sand, if the plant selection needs better drainage. Perlite will do the same job but note that vermiculite has a pH of 7-8, making it unsuitable for ericaceous plants.
Watering is essential for containers. Rain alone won’t usually be sufficient to keep your plants healthy and happy – much of it will simply bounce of the leaf canopy and if it is densely planted, very little will penetrate the soil. Materials like terracotta will likewise wick moisture out of the compost.
A deep draught, periodically, is preferable to a ‘little and often’ approach. If you have a collection of plants, then you might consider an irrigation system where a number of containers are served by a series of hoses and feeders, linked up to an outdoor tap with a timer to come on once, or twice a day, usually at dawn or dusk. I have this at home and can go away on holiday with a clear conscience and without bothering the neighbours.
The compost you use will help feed the plants for a few weeks, but if something is quite dynamic, flowering extravagantly, or fruiting, then some additional nutrition will be needed regularly over the life of the display. A general fertilise will contain the basic nutrients and something like tomato food is good for flowering displays as it is high in Potassium (K), as well as Nitrogen (N) for healthy leaf growth and Phosphorus (P) for root growth. I prefer liquid seaweed and this can be used as a drench, but also as a foliar feed if you put it into a sprayer. Seasonally changing displays can be fed throughout the life of the selection. For permanently planted containers with mature trees and shrubs, start in March and stop by the end of August.
You may prefer to use a slow-release fertiliser, little spherical pellets that release their chemical over several months. These can be mixed in with the compost when filling the pot.
On the day of the workshop, despite my comments above as to what should have been available, well I still had a wealth of plants to choose from and subsequently planted up several containers from the selection to hand.
We used Heuchera, heather, a beautifully richly-coloured Echinacea, Muelhenbeckia and violas in the metal container above. The violas will flower right through until Spring, in all but the coldest weeks of winter, the Heuchera and Muelhenbeckia, which hails from New Zealand, are evergreen, or ever-copper as it were, and the heather will maintain its colour for several weeks before new green growth sprouts at the tips.
In the two faux-bois troughs above, we used Heuchera again, with pansies to tone in with the dwarf Anemone Fantasy Pocohontas and the sparkling yellow Coropsis. Burgundy creeping Ajuga picked up the tones in the pansies, as well as the underside of the leaves of Heuchera. Mint added a lush green, as well as fragrance and the grass, Carex, both obscures and reveals the underplanting, and adds a dynamic touch to an otherwise static planting. I think I also added some silver-leaved Lamium to the mix. I will have to have a look at the planters in situ. Lysimachia numularia Aurea punches a little more lime into the mix and will trail.
Pansies and their smaller relatives the Viola, come in a myriad colours and many have a beautiful light scent too; what’s not to love.
I mocked up, but didn’t plant, a large black container, with a diameter of at least 55cm and a depth of 50cm, with tall grasses, and a golden Crocosmia George Davidson, which has elegant straplike leaves and a spray of flowers on a long stem. Anemantheles, the Pheasant Tail Grass is evergreen, and develops rich warm tones of russet, ruby and gold as autumn progresses. I think I added Panicum Heavy Metal, with delicate seedheads, but overall, the effect was spare, with elegant stems and an airy upright, tall effect. One guest at the workshop returned a little time afterwards, and we recreated this but added Cornus alba Sibirica, with red stems and autumn-tinted leaves, fringed with Muelhenbeckia, daisy-flowered Erigeron karvinskianus and Viola Honeybee, which blended with the warm tones of the grasses. The composition worked really well.
One final planter included an autumn flowering (in blue) evergreen Hebe, another Carex grass, bronze this time, mint for contrast, sempervivums and burgundy Ajuga. Golden Thyme too.
Sitting here in the office at Petersham Nurseries, as I write this, I am looking out at another container that I planted up earlier this year. A richly decorated Italian Poggi Ugo pot, at least 50cm wide and deep, is home to Rose Lady Emma Hamilton, Salvia Ember’s Wish, Erigeron and blue Geraneum Rozanne. The rose has bronze foliage as it emerges, turning green as it matures, and this was a compliment to the terracotta the pot is made in. The red Salvia picks up the flashes of raspberry on the reverse of the rose petals, which are otherwise a bright tangerine, fading to apricot. The daisies sparkle and the china blue of the Geraneum,, adds contrast . Evergreen Muelhenbeckia trails and the daisies pick up the white eye of Rozanne. It has been a joy all summer and is still looking good.
Roses are fine subjects for container planting, but be aware they are hungry, greedy and thirsty things; use a John Innes #3 compost, or the Claybuster wool compost, that is otherwise used as a mulch, or used to lighten heavier clay soils. Feed the roses right through the season, until the end of August, with a liquid rose food, or liquid seaweed.
At David Austin’s gardens in Albrighton, they showcase roses in a variety of containers and they look fabulous. There are several galleries in this blog, so please do have a look.
Finally, I would mention the planters we created for Britain in Bloom – stone horse troughs planted up in July that are still looking good, on the Petersham Road towards Sandy Lane, opposite Ham Common and by the shops on Ham Parade. The Gaura, Geraneum Rozanne, Sedums and Erigeron in two of them are still blooming several months on. The third, by Ham Common, has white Fuchsia Annabelle, lots of Heurchera and Rodgersia but the star is undoubtedly Salvia Ember’s Wish (as above). It positively glows in the afternoon sun and is a lavish feast of deep red flowers on tall, elegant stems. It is my favourite of these three planters