As we have moved away from the quarter-acre section to high-density townhouses and apartments, landscapers have had to learn new skills to accommodate gardens that match this trend. Here, expert Jon Muller shares his top tips for landscaping with planters
People living in high-density housing and apartments lack the space for a traditional garden, but that doesn’t mean their life needs to be lived without green spaces. One way you can provide that is via planters.
The advantages of growing plants in containers or planters are that you can modify the growing medium to suit the plants and determine the size and height of the container.
The key things landscapers must get right to ensure plants flourish in planters are:
The substrate or base for the planters.
The type of container.
The growing medium.
The plants.
The substrate or base of the planters
Materials used for the substrate or base of the planters vary but could be a timber deck or a concrete pad with tiles. However, it’s important to know the loading of the planters on the deck or pad, otherwise you could run into trouble further down the line.
Be aware that large planters are very heavy once filled. These planters can sit on a solid concrete base or plastic composite decking on a subframe over solid concrete, as both bases can handle the load. However, large planters are not always suitable. For example, on a nearby job we wanted to do something similar with tiles over adjustable pedestals on a concrete base. We decided to not go ahead, as the weight of the planters over the tiles would have most likely broken them. If you are in doubt, you can check with an engineer if the loading is OK.
The containers
You can use a range of containers, from large round pots to rectangular planters like the ones shown. Containers come in different materials, such as:
Terracotta
These pots can be glazed or unglazed. Unglazed pots are more porous than glazed ones, which allows water to seep through the pot. Be mindful that terracotta can break easily.
Metal
Aluminium is best as it is light, durable, malleable and doesn’t rust. However, be mindful that it can corrode. It can heat up like most metals, but it dissipates heat easily.
Hypertufa
This container is made from a mix of one part cement, one part peat moss and one part perlite or vermiculite.
Timber
You can build raised gardens from timber, but it should be made from tanalised timber. If you are growing edible plants, you should line the inside of the planter with weed mat to reduce the chance of tanalised leachate in your planter mix.
Plastic or fibreglass
These are light, durable and can come in a range of colours and styles.
The larger planter shown on the left is made from aluminium to fit the dimensions of the site and powder coated to withstand the strong coastal winds nearby.
It is best to use a light, neutral colour, which allows the plants to be the centre of attention. Additionally, a metal planter painted with a neutral colour means it’s less likely to heat up as much as dark colours. Keep in mind that timber planters and adjacent timber structures can look great in black, as the green plants ’pop’ against a dark background.
Drainage holes in the base of the planters/pots are crucial and it’s a good idea to place broken terracotta pot pieces over the holes to allow water to drain. The planters and pots also need to have cleats to provide a gap for the water to drain away, plus, if they are on timber decks, the cleats provide an air gap to reduce the chance of timber rotting.
You can also place the pot on a tray as below. Note the use of the kitty litter on the tray to absorb any brown leachate from the potting mix rather than stain the tiles.
You can also insert lighting spikes into planters and irrigation as trickle irrigation. You can then adjust the irrigation needs for each planter if you have adjustable irrigation.
The container mix
It is important to get your container mix correct, as you’re restricting your plant roots in a confined container. The mix needs to have adequate nutrients, hold moisture and ensure water drains away easily. The mix also needs to be relatively 'open' to allow roots to spread easily.
For large pots, I use potting mix in bags, although you can now buy container mixes in bags for outdoors as well. If using large containers, you can try your local supplier, but make sure you get a good mix to suit the conditions.
A word of warning – I once purchased what I was told was a garden mix with compost and some good loamy soil but found out the compost wasn’t properly composted, so it leached onto the tiles, which was an issue. It took a while for the leachate to dissipate. Ideally, use a mix much like a good potting mix with long-term slow-release fertilisers added. We used to use peat-based potting mixes, but now most are bark-based. If you are mixing soil with compost, make sure the soil is free of weeds and debris and has good structure.
Plants
As always, plants need to match the environment. The three main types of plants to use are:
Focal point plants; eg, Xeronema callistemon.
Fillers; eg, Hebe Wiri Mist.
Spillers or trailers; eg, rosemary.
Try to get a mix of darker and lighter colours with your plants and mix softer textures with more bold textures.
In this coastal environment, the following plants were used:
Trailing plants:
Rosmarinus ‘Lockwood de Forest’.
Lobelia angulata (syn Pratia angulata).
Disphyma australe subsp australe.
Ground covers (fillers):
Pimelia prostrata.
Alyssum (annual but self-seeds).
Shrubs (fillers):
Hebe ‘Wiri Mist’.
Corokia ‘Geentys Green’.
Brachyglottis greyi.
Xeronema callistemon (focal point).
Trees:
Cordyline australis.
Griselinia littoralis.
Jon Muller has owned Wellington Gardens Ltd for 24 years. He practices landscape design and construction, with an emphasis on planting design.
He has taught at polytechnics and university, mostly in soft landscape subjects. He has written six gardening books, including Wellington Gardens, and enjoys helping clients find landscape solutions. He also helps students and workers studying for their landscape qualifications.