If you live in New Zealand, the chances are you’ll need to manage a garden influenced by coastal conditions. In this article, horticulture expert Jon Muller explains how
New Zealand is surrounded by ocean. Coupled with very strong winds, salty conditions can be very harsh on plants and metal or timber structures.
Recently, in Wellington we had 130kph winds, which meant that plants near the coast were badly burnt off and trees were damaged. Canterbury has had two instances recently where they had 150kph winds in Christchurch and 200kph winds on Banks Peninsula. There was widespread damage to trees, as expected.
Our coastal soils are either rocky or sandy, which means they don’t hold water well and are low in nutrients, unlike clay or silty soils. As coastal areas seldom get frosts, most coastal plants are frost tender.
Dry and mighty
Plants that handle dry conditions like this are called xerophytes (dry plants). These plants have adapted their growth to handle the dry conditions in different ways.
In plants like the native groundcover Disphyma australe (horokaka), the fleshy leaves store water to weather the dry conditions.
Other plants reduce the loss of water to these harsh conditions by having glossy leaves, such as Coprosma repens (taupata), or furry leaves such as Brachyglottis greyi. Metrosideros excelsa (pohutukawa) gets the best of both worlds with a glossy upper leaf surface and furry underside.
Other plants have rolled leaves, like Apodasmia similis (oioi) as well as having waxy leaves which, reduces water loss.
Other plants, known as halophytes, such as Juncus maritimus, can grow in very salty conditions and not suffer water loss, due to the very saline conditions drawing the water out of the plant.
Coast to coast
When planting in coastal conditions, our native coastal plants do well, but allow for regional differences. For example, cabbage trees growing in Canterbury have subtle differences to those growing naturally in Northland. You can also use coastal plants from the Mediterranean, like Rosmarinus (rosemary), Australian natives like Grevillea, or South African plants like Carpobrotus.
If growing these plants, you need soils with excellent drainage if you are creating a garden from scratch. Also, coastal plants don’t need a lot of fertilisers, especially members of the Protea family like Grevillea.
Plants for different purposes for coastal gardens are suggested below:
1.Large trees for marine boulevards:
Araucaria heterophylla (Norfolk pine)
Banksia integrifolia
Lagunaria patersonii
Metrosideros excelsa (pohutukawa)
2.Smaller trees:
Cordyline australi, (ti kouka)
Meryta sinclairii (puka)
Myoporum laetum (ngaio)
Olearia paniculata (akiraho)
Pittosporum crassifolium (karo)
3.Groundcovers:
Disphyma australe
Coprosma kirkii
Osteospermum ecklonis
Pimelia prostrata
4.Shrubs:
Hebe speciosa
Pachystegia insignis (grow in stony soils)
Senecio greyii
5.Grasses and grass-like plants:
Anemanthele lessoniana (wind grass)
Carex Testacea
Cortaderia fulvida, (toetoe)
Desmoschoenus spiralis (pingao)
Phormium cookianum (wharaiki)
Poa cita (silver tussock or wi)
Xeronema callistemon (grow in pots or stony soils)
Lawns
You can use native coastal groundcovers as a lawn, such as Selleira radicans, remuremu.
You plant these plants as plugs, or small plants from a tray in free draining soils about 20cm apart. In time they form a dense mat. You can spray salt water over them and they will survive but the salt water will kill seedling weeds.
From experience, make sure you keep an eye on invasive weeds like clover as they can take over and smother the new Selliera plants. They also have special fertilisers recommended for them. There are nurseries that specialise in no-mow plants for lawns, both coastal and inland.
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.