Monday 22 January 2018

Diarmuid Gavin’s garden action plan

Many renters and apartment dwellers are faced with limited space - and limited soil - in which to create a garden. Here, our renowned garden expert gives his guide to planting in pots and containers, which can be packed up and taken with you

Diarmuid Gavin: a potted garden will work equally well on a deck or patio. Photo: Fran Veale
Diarmuid Gavin: a potted garden will work equally well on a deck or patio. Photo: Fran Veale
Bay tree
Zantedeschia / Easter lily
Nasturtium in terracotta pot

Diarmuid Gavin

Welcome to Week 3 of my Garden Action Plan. This week, I will show you how to create a garden of pots and containers. The contemporary gardener often prefers not to be a slave to their plots. And the spaces they garden in are increasingly small. Gone are the times when suburban estates were built with tennis-court sized gardens. We live in an era of high-density housing where every space, indoor or out, carries a premium.

Apartment blocks spring up in docklands and even the suburbs with gay abandon. And the private outdoor space they offer can range from balconies to rooftop terraces. There is an increasing need to create gardens in places where there is no direct access to the soil, such as on top of a concrete slab in an apartment block courtyard where there’s a car park underneath.

Younger gardeners tend to be style-conscious consumers who are attracted to architectural plants in striking containers.

They love the idea of being able to go to the garden centre, buy a few plants, a pot and some compost and transform their courtyards, terraces or balconies in one fell swoop. In this new age of gardening, what in the past may have been considered as  unusual spaces are regarded as having potential for greening. Gardens have now even been driven up the walls as the vogue for vertical planting takes over hipper areas of our cities.

A potted garden will work equally well on a deck or patio. It is also the perfect option for those of you who are renting houses and apartments: using pots, you can create a beautiful garden that can be packed up and taken with you when you move.

The concept of containerising is an ancient one. People have always wished to tame nature and have selected what they liked or needed from ‘the wild’ and created an environment for the plants near their dwellings to provide food, or for an aesthetic purpose. However, placing plants in some type of container means that you are in charge of almost all the nutrients, trace elements and, most importantly, the water that your plants have access to. So whether you’re a new trend-inspired gardener or someone who’s set in their garden ways, here’s my guide to how to plan for a successful potted paradise.

Garden action plan: Potted garden

1 When planning your container garden, use the highest quality materials, growing mediums and maintenance systems. The installation of permanent potted gardens on places like roof terraces or city courtyards can take a substantial investment.

2 Carefully examine your containers of choice. If you are using a clay pot, ensure that it is big enough to sustain what you want to grow in it. If you are in an environment which gets cold, make sure that the pot is frost resistant.

3 If you are using metal pots, make sure that they are suitable for wet environments. Mild steel will rust unless it has been powder coated, galvanised or painted in a water-resistant coating. I often try and ensure some type of insulation by introducing a coating of foam or polystyrene sheeting between the compost and the outer metal layer.

4 If you are using wooden containers, ensure that they have been treated with a preservative and wherever you are setting them, allow for good air flow all around.

5 There are other materials available for planters such as plastic and fibreglass. Make sure your chosen one is suitable for outdoors and won’t crack or be quickly diminished through exposure to ultraviolet light.

6 Whatever your container is made from, ensure you have drainage holes. Very few plants like to sit in a damp environment. These drainage holes should be just the right size — you don’t want compost and nutrients leaching away with every watering.

7 Use fresh fertile soil or compost. Try to ensure that your choice of growing medium is suitable for the plants that you’d like to grow — for instance, some species such as rhododendron (best kept to containers because of its invasive tendencies) will like an acidic base. So make sure of the pH of your soil is correct.

8 Consider what compost you are going to use and how hungry the species you are planting are going to be. A free-draining John Innes-based compost can be an excellent choice for containerised plants.

9 Add extra slow-release fertiliser into the mix, and if you have any humus material — such as well-rotted farmyard manure — place a layer of this well out of the way of the roots of the plant.

10 Some containers will benefit from the ­addition of gel pellets which absorb up to five times their volume and weight in water. These will act like capillary mats, capturing moisture and releasing it as and when the roots require.

11 When you are considering planting large containers and setting them in a permanent or semi-permanent positions, make your decision about what’s going where while they are still empty. Moving a container that’s been half-filled, or filled with compost and planted, may be difficult — and pushing or shoving may damage either the planting or structure.

12 With large containers, start with some grit or pebble covering a layer of 2-3cm at the base. This will add drainage and aid air circulation and the exchange of gases. If you are gardening on a balcony, rooftop or another situation where weight is an issue, polystyrene balls available from an upholstery shop may be a good lighter drainage aid option.

13 Many different types of plants are ­suitable for containers — choices can be made from trees, shrubs, herbaceous ­perennials, ­grasses and bulbs. Permanent arrangements of plants can be enhanced by seasonal colour. Bluebells, dwarf ­narcissi, anemones, chionodoxa and tulips can look wonderful set in a drift under a containerised ­multi-stemmed birch, or putting on a performance before the flowering of herbaceous perennials.

14 Don’t squeeze a plant into too small a ­container or pot as you will damage the roots and certainly restrict future growth of the plant.

15 If you are using unglazed terracotta pots, dunk them in water for 24 hours so they don’t absorb all the moisture away from the roots of your new plants. With other containers, dunk the plants themselves in water for 30 seconds or so before planting so the rootballs are well and truly moist before they go into new compost.

16 Water a newly planted container thoroughly and carefully. Let the water soak in, stop briefly and then soak again. In exposed situations, it may be advisable to use a mulch of flat slate or forest bark.

17 With bigger specimens such as trees or large bamboos, make sure you have some help to lift them about. You’ll require plenty of room in the pot for root growth. Large trees may need an anchoring system, especially if they are to be sited in an exposed place on a roof.

18 Never let your containers dry out. At different times of the year, they will need more or less watering. A hanging basket raised in the air will be dried out by the surrounding breeze as much as the plants within it looking for water. This may have to be watered twice a day during the times when the plants are putting on vigorous growth.

19 All containerised plants will benefit from feeding. Trees and shrubs are often neglected, but a mulch of well-rotted manure, a sprinkle of granular fertiliser raked into the top few centimetres of soil or a top dressing — replacing old compost with new — will produce rewards. Foliar feeds will provide an instant boost.

20 The key to the success of your planted container will be in both regular irrigation and occasional feeding. Many plants are put under stress or perish during holiday periods so an irrigation system on a timer may be vital. Ensure that excess water can drain away, not only through the drainage holes in your pot but also from the ground beneath which it is sited.

My top 10 plant choices for pots and containers


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Nasturtium in terracotta pot

One of the simplest plants to grow from seed, and a great one to try out with the kids or grandchildren. The seeds are big so are easy to handle, the first leaves pushing up from the soil are very distinct and they thrive in poor soil. Too rich a soil will result in too much foliage and less flowers. Sow directly into pots outdoors in April or May. 

Bay (Laurus nobilis)

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Bay tree

Clipped into simple topiary shapes such as cones and balls, this evergreen always provides an elegant look.


If you love bamboos but are concerned about them spreading, pots are a great way of containing them. They can dry out easily, so a good watering regime activated in mid-March every year is essential.

Verbena bonariensis

This tall purple-flowering plant makes for a striking container option. It grows in a rather statuesque way, tall and slender, dramatic and architectural as a specimen on its own.

Erysimum ‘Bowles’s Mauve’ 

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With its small mauve flowers which keep going from spring through to autumn — and often beyond, this understated beauty performs well in sun or shade. It will pair well with other cottage garden plants, such as hardy geraniums.

Japanese maples

Specimen Japanese maple trees grow beautifully in wooden tubs. Some species look great with their arching framework of branches reaching lower than soil level, so elevating them in a container allows the crown to spread naturally and beautifully. Maintenance is key — top dress without disturbing roots near the surface, and every five or six years, take the plunge  and repot.


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Zantedeschia / Easter lily

Known as the Easter Lily, this plant creates an almost tropical dramatic statement with its lush arrow-shaped leaves and brilliant white flowers with yellow stamens. They like to be wet, so keep their feet as damp as possible by placing a saucer beneath a pot to collect excess water.

Stipa gigantea (Golden oats)

Standing up to 8ft tall and 4ft wide, this grass makes a striking statement. It’s easy to grow and likes an open, sunny position with well-drained soil. Cut back once a year to allow new foliage to emerge in spring.

‘Ballerina’ apple tree 

Perfect for apartment and balcony dwellers who’d really love to grow some fruit, this type of miniature tree, where short flowering and fruiting spurs are produced, could be ideal. One central column can give you plenty of apples.


This is the ultimate pot plant, tough as old nails with a desire for a sunny position. Rosemary grows in either upright or trailing form, and is handy for keen cooks.

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