Containerplanting for balconies, terraces and roofgardens

21. February 2021 by Isabelle Van Groeningen
Categories: About gardening, english, Seasons, Spring | Tags: , , | Leave a comment

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Containerbepflanzung - Frühlingsgefühle © Isabelle Van Groeningen
Frühlingsgefühle

Flagge Deutschland für deutsche Übersetzungauf Deutsch lesen – As spring approaches, it is not only beds and borders that need our attention, the same goes for containers on terraces, roofgardens and balconies. On the one hand I enjoy the flexibility of plants in pots, as you can move them about and rearrange them. As plants come into flower, you can re-decorate, mix and match to your hearts’ content. On the other hand I dislike the total dependency of these plants far removed from their natural growing environments.

Dependency

Container plants are like a patient in intensive care: they are fully dependent on people to see to all their needs. You cannot walk past a desperately dry plant, thinking you’ll water it in the morning. You need to do it there and then. The same goes for the feeding regime. In a well-balanced garden, like in the plant’s native habitat, mother nature takes care of most, if not all, nutritious needs your plant may require. So the responsibility lies with you: keep an eye on your plants, check them regularly to make sure they are happy. A happy plant will reward you with long-lasting flourishing presence.

Soils

There are numerous potting composts on the market, ranging from pure peat to peat-free, with or without loam, composted plant material such as green waste or bark and/or by- products from industry like coir. Some are better than others. Buy from a company that is known for specialising in growing media. Avoid buying cheap no-name compost in the supermarket, this may be ok, it may not. Although I tend to favour all-purpose composts from most plants, there are a few where it is worth buying a specific mixture. Citrus plants, succulents, for example require special soils. Edible plants must be grown with fertilisers that are approved for food production, and of course all plants related to heathers and rhododendrons require soil with a low pH. As pots are often watered with tap-water rather than rainwater, there will be a progressive build-up of the pH level in the soil, which can lead to the plant having difficulties accessing nutrients so all the more important to give these plants the right soil and fertiliser.

Fertiliser

Usually potting composts have an appropriate slow-release fertiliser incorporated. How long this lasts depends on the product, but also on the plant and the container-size. A large, leafy plant in a relatively small pot, or a container filled with many plants, will soon use up whatever the soil has to offer. The first 6-8 weeks plants should be fine, but always be vigilant. As soon as you notice plants diminish in vigour, slow down their flower production, or start to show abnormal discoloration in the leaves, consider feeding. The fertiliser will not last more than one season, so do feed your old familiar friends as spring comes.

How often do you have to repot?

If in a large enough pot, trees, shrubs and perennials can survive several seasons without the need for re-potting. When the time comes, you will notice the plant loosing vigour and beauty. You can try to scrape off some soil from the surface and replace it with a layer of fresh soil. This is only a temporary solution that may see you through to the end of the season. Either move the plant into a larger pot, alternatively, you can carefully trim some of the roots and re-use the old one. The famous square wooden Versailles planters were so designed that side panels can be slid out, so that you can trim the roots on one side, before slotting in the panel again, and adding some fresh soil. Early spring is a good time to do this, as the plants have just come through their winter resting period, and as days lengthen and temperatures increase, they are rearing to get on with life.

What do you want to grow, what do you need?

Before you rush off to buy plants, think about what you want or what the plants should do for you. Just like planning a bed or border, you need to have a concept in order for it to be successful. If not, you will just end up with an amalgamation of pots and plant that will, or more likely will not, fit together.

Screening: You may want some shade, a wind break, something to absorb noise or you just want to stop gawping neighbours from seeing what you have for lunch. Do you need screening summer and winter, from spring when plants start to emerge, or only at the time of year you are sitting out?

Container-Bepflanzung - Sichtschutz © Isabelle Van Groeningen
Diversity – in plants and pots

All year screening is best achieved by evergreen shrubs or hedge, possibly yew. Not many evergreens are truly hardy. Remember that in pots they will be even more susceptible to frost damage than when they have their feet in the soil. A permanent fixed screen in the form of lattice work pergola or bamboo mats will also help.

Container-Bepflanzung - Sichtschutz © Isabelle Van Groeningen
White begonias and high-stem panicle hydrangeas provide easy protection on this shady terrace

Seasonal screening can be achieved by planting trees or shrubs that come into leaf in spring such as Japanese maples, crab apples and cherries. Not only are they hardier, they allow more light through in winter. If you choose carefully you will have the added bonus of flowers, possibly fruit, autumn colour and attractive winter stems like birches or Cornus alba ‘Sibirica’.

Container-Bepflanzung - Sichtschutz © Isabelle Van Groeningen
Bamboo mats Plastic plants and flamingos distract the eye all year round …

Where height rather than bulk is required, use a simple climbing frame or pergola with a climber such as clematis, wisteria or rose. Annual climbers like sweetpeas, Ipomea or black eyed Susan are quick and colourful. If you are looking for height, then use espalier fruit (ornamental or edible) and umbrella-trained trees such as planes, limes or Liquidamber styraciflua. Tall perennials and grasses can also be useful, tough remember that many of these may not reach their final flowering height till mid to late summer. Calamagrostis x acutiflora ‘Karl Foerster’ is a useful, having reached 1,7m by early June.

Container-Bepflanzung - Sichtschutz © Isabelle Van Groeningen
With a large variety of plants in refreshingly white colors, the entire balcony is protected so that nobody looks up

Plant choice

Container-Bepflanzung - Erfolgsgeschichte © Isabelle Van Groeningen
Story of success: for a sunny terrace: The geranium cascade is very successful, but is not a hit with local insects.

Just like in a garden, you must consider the light requirements for your plants. A shady balcony will not deliver happy healthy roses, juicy red tomatoes or a flowering cascade of Geraniums like on a Bavarian balcony. If you only have limited sunlight (a few hours in the morning or evening) choose shade lovers such as begonias, buzzy-lizzies for summer flowers, herbaceous geraniums ferns and hostas as long-lived attractive perennials, dwarf rhododendrons, azaleas and hydrangeas as flowering shrubs. If you want edible goodies, concentrate your efforts on soft herbs such as parsley, chervil, coriander and dill. leafy veg such as spinach, chard and salads. Alpine strawberries and raspberries can provide something for the sweet tooth.

Mixing plants

I always like to plant a mixture of plants so that there is some structure in the winter, and I do not need to replant everything every year. This saves on a lot of work and compost. A few long-lived woody plants provide all-year structure and perennials come back each season. When carefully chosen, they will also provide good winter silhouettes. They also offer much more wildlife benefits thanks to additional feeding, nesting and hibernation opportunities. A long-lasting splash of colour can then be added with some seasonal flowers.

Container-Bepflanzung - Mehrjährig Schatten © Isabelle Van Groeningen
Perennial shade: hardy Fuchsia magellanica ‘Alba’ blooms all summer long and creates a nice contrast with the large hosta leaves. Hosta ‘Harry Van Trier’ is particularly suitable for pots: compact, free-flowering, with good autumn colors.

Do not mix the short-lived and perennial in one planter: it is difficult in year two to find space for the new root balls, and the newly planted flowers will have difficulty to get established in the tight root system of others.

Container-Bepflanzung - Mehrjähig für Sonne © Isabelle Van Groeningen
Container – Perennial for sun


The drawback of having a great variety of plants (woody, perennial, edible, annual), is that there may be a lack of unity in the planting scheme. A specific colour scheme helps to create harmony, or using one or two plants that recur regularly. Instead of planting buzzy-lizzies as well as begonias, plant only one type and colour of begonia, or add several identical ferns to draw together the whole scheme.

Container-Bepflanzung - Mehrjährig für Sonne © Isabelle Van Groeningen
You can hide well behind high Salvias (S. ‘May Night’), otherwise it is nicer to look down on them (Ahillea ‘Pommegranat’ and Artemisia ‘Powys Castle’.

Containers

If possible choose identical containers, or at least settle on one material or colour. This helps to bring calm in the chaos. The plants should draw your attention, not the large variety of pots you have accumulated over the years.
Make sure they are suitable for outdoor use and resistant to frost. They need to have adequate drainage holes so excess water can flow off. Terracotta pots should be elevated off the ground on little feet, that excess water can drain away to prevent the pot form cracking in hard frosts. In summer I like to use saucers or trays, as they catch some excess water which can be helpful during particularly hot days.

Container-Bepflanzung - Räume schaffen © Isabelle Van Groeningen
Creating space: With larger tubs it is possible to create spaces and a lot of privacy tubs

Remember to check the weight-bearing limit of any terrace or balcony before you start! If weight is an issue, use light-weight pots and compost. The range of light, high-quality man- made materials is forever expanding.

Rather use two large pots than six small ones. The more space roots have to grow and develop, the happier the plant will. Large pots do not dry out as quickly, they also stay cooler on hot summers days. Woody plants, particularly roses, produce deep roots, and will need a taller pot: 50cm or more.

Container-Bepflanzung - Vielfalt © Isabelle Van Groeningen
Container plants – mixed trees such as Birch, hemp palm and hydrangeas offer a view and shelter from the wind on this roof terrace

Not only are potted plants fully dependent on you watering and feeding them on time, they are generally much more exposed and susceptible to weather extremes. On hot sunny days, the pots warm up, adding even more stress to a root system which is designed to be hiding in cool damp soil. With this in mind, I avoid dark-coloured containers. Dark grey or black metal can get very hot in summer. The same problem occurs during harsh cold winter conditions. The likelihood that the roots are frozen, whilst the above-ground part of the plant struggles to access water as the gentle warming rays of winter sun shine on its leaves.

Keep a vigilant eye on your plants to make sure they are fine. But do not take it personally if one decides to part company. There can be so many reasons why this happened, many of them have nothing to do with the care you gave. And where one goes, place becomes available for a new one!

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