In real estate, the saying goes “location, location, location”, which suggests that where your house is located will give you the best results in value. As gardening expert Jon Muller explains, the same is true in horticulture
All plants come from different zones around the world. For example, one plant grows naturally in a northern hemisphere woodland environment, and another one in a southern hemisphere coastal environment. If you try to grow the woodland plant, which likes shady, moist conditions, in a coastal environment, which has sunny, drier conditions with salt laden winds, your success rate won’t be high. For example, try growing a magnolia, which likes woodland conditions in a windy, dry spot and it will suffer or could die.
In my Wellington Gardens book, I mention the Wellington Regional Council “ecological zones” around the region. You may have similar zones in your area, but you can base your zones on the climatic factors of light, wind, temperature and water. As well as these climatic factors, your area’s soil type will have a big influence on plant growth.
Always get your bearings
One of the first things I do when looking at a garden is to get my bearings. That is, which way your client’s garden faces. This is called the aspect. The aspect has a big bearing on the climatic factors such as light, wind, water and temperature. For example, if your client’s property faces north and the prevailing wind is north-west, then you will get more sun and warmth but more wind, which will dry the soil out.
Additionally, once you get your bearings, you know that to the east you will get morning sun and, to the west, late afternoon sun. The other factor to consider is topography, which means the “slope” of the land. Let’s say your client’s land slopes towards the east. That means they will get early morning sun, but not sun later in the day, as the sun to the west will be blocked by the west hills.
If your client’s land has a very steep topography, it can mean water will drain quickly compared to if the land is at the bottom of the slope, which means it will collect water. However, your client’s property may be more prone to erosion and the land slipping.
It’s also important to know what your prevailing wind is. For example, in Wellington it’s the north westerlies and in Auckland it’s south westerlies. That’s because wind can distort the growth of plants, even if they are tolerant of it. Check if the winds in your client’s garden are salt laden, which will determine which plants can be grown in the area. For example, if the winds are salt laden, stick to coastal plants. Wind has a chilling effect on plants, as well as potentially causing damage, so consider this as well.
Look for your weakest link
Another saying is “the weakest link determines the strength of the chain”. So, you need to work out what the limiting factor is in your local area. Wind is a common limiting factor, especially in Wellington. Weather extremes also make it hard to work out limiting factors, as your bank might be fine to grow plants until you get a one in 100-year rain, and the bank and all your client’s plants slip away. That’s another reason to always check drainage and bank stability when inspecting a site!
Your client’s soil has a big influence on plant growth. Sandy soils drain well, but don’t retain nutrients and water. Clay soils hold moisture and nutrients, but don’t drain well. The ideal soil is a silt loam, as they retain moisture and nutrients but drain adequately.
To match or defy climatic factors
You can either match your client’s plants to the climatic factors of soil, topography and aspect, or modify the factors to allow other less tolerant plants to grow. You can’t change the aspect or topography, but you could change the soil by adding organic matter, provide shelter to reduce wind, or irrigation to increase moisture.
For example, I was asked about a very windy site in the Wairarapa, where a client had planted Griselinia littoralis (kapuka) and all had died off. The soils were poorly drained, and there were frosts. Kapuka are normally very wind tolerant, including salt-laden winds, and are also frost hardy, but can’t tolerate wet feet. I suggested creating a mound and planting Phormium tenax (harakeke) on the windward side of the mound and, once they grew up, plant the kapuka behind the harakeke on the leeward side.
The mound and low planting modified the climatic factors enough to give the kapuka a head start. The biggest limiting factor in this case is mostly likely the wet soil, followed by the wind. By planting harakeke, which tolerates wet soils, it provides shelter for the kapuka. Creating a mound is a great way of improving drainage as well as reducing the wind.
On the right are some examples of plants for different conditions.
Plants that like dry, shady conditions
For example, under a tree:
Plants that like wet conditions
Plants that like coastal conditions
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.