Gareth Carter: Trees that throw the right kind of shade

Silk trees (Albizia julibrissin) are currently in flower around Whanganui.

On a hot summer’s day, the value of a tree is sought-after. At parks, a tree becomes the favoured place to put the picnic rug and bask in the cool dappled shade it offers. In a carpark, having the car under a tree will help keep the vehicle from being so hot upon its owner’s return. Planting trees on the west side of your house will provide shading to your abode that will reduce the solar gain and temperatures inside the home.

I was talking to a passive house expert this week who gave the example that, during the summer months, windows in a home are like a heatpump, adding kilowatts of heat into a home.

Going further with this thought - if a tree blocks out the heat, your house will not overheat as much on these super-hot summer days.

This is where planting deciduous trees which drop their leaves in the autumn offers so much value. They provide shade during the hot months and allow sun through during the cooler months, when more solar gain is advantageous and desired.

If you have ever thought a shade tree in the back yard would be nice, it was probably during hot summer days like what we are having now - a tree to dapple the strong sunshine and provide some relief from the heat; a tree to sit beneath and read a book, or for the kids to play under without getting sunburned.

A shade sail could provide the same sun protection, but it does not have the same cooling effect as a tree. The mass of water stored in a tree, which travels from the soil into the roots, through the trunk and branches then evaporates out the leaves, provides a cooling effect that is unsurpassed.

In situations where you need the tree to also provide privacy from neighbours or remove an object from view, an evergreen may be a better choice.

There is a great selection of trees that will provide excellent shade. The skill is to choose one that will meet your needs. Things to consider are what size you would like, what space is available, if you would like it to flower and if you would like something with good autumn foliage colours for seasonal interest. These need to combine with practical considerations, such as soil type, exposure to wind, frost, cold, coastal salt spray etc, to ensure the tree’s successful growth.

For a smaller town section, one must consider the shade a tree may create for a neighbour, so smaller growing varieties or trees that respond well to pruning will be a better choice.

Here are a few good options:

Cercis Forest Pansy is a stunning smaller growing deciduous tree suitable for many town gardens. Popular for its deep burgundy foliage colour, Forest Pansy can be kept tidy to around three metres tall and three metres wide, providing a wonderful shade tree for a small courtyard situation. If left untrimmed, Forest Pansy will grow to about five metres.

Flowering cherries (prunus) are a very popular choice of shade tree. There are a number of varieties that all have slightly different growth habits. This means if it’s a flowering cherry you want, you can usually find one that will grow to fit the space you have available. Kanzan is a taller growing variety with spectacular double pink flowers and forms a vase-shaped head, while Pink Perfection has a very similar flower, but its growth habit is far more spreading, so it forms a better shade tree if it’s width you need. Jim’s Delight is a relatively new release and only reaches three metres high - a real little gem if you want a small shade tree for a tight corner. It has spectacular single pink blossom in the early spring, as well as spectacular autumn foliage as the leaves turn shades of red and orange.

A top-selling flowering cherry tree is Shimidsu Sakura. This has an excellent spreading umbrella-shaped growth habit. It will grow to about four metres high by five metres wide and, as well as being an excellent shade tree for the summer, it puts on a spectacular show in October, with deep pink buds opening to double white flowers with pink tones. Shimidsu Sakura also has a good display of autumn colours, with leaves turning tones of orange and yellow before dropping.

Silk tree (Albizia julibrissin) is another excellent shade tree. In flower at the moment, you will be able to spot them around the city, with their mass of fluffy pinky-red flowers covering the trees. Hotter summers seem to improve the flowering of these trees. The silk trees have distinctively soft, ferny foliage which lends itself to providing good dappled shade from its naturally spreading branches. These trees, if left to grow, will reach about six metres tall and five metres wide, but they are easily pruned to a much smaller size. They grow quickly, so good shade can be established in three to four years.

Driving around the city, I have also seen some magnificent jacaranda in flower, with their cool bluey-purple blooms. These can also be kept smaller with pruning.

Fruit trees can also make good shade trees. A plum tree at the bottom of the garden can make an excellent shade tree, with a mass of white blossom in the spring and then an abundant crop of fruit around Christmas. The added bonus is the fast growth rate of plum trees, from which shade can be established, and they can be pruned to size. So, why not make your shade tree productive and choose a plum or other fruit tree?

Cherry trees also make good shade trees. I have talked about the beauty and good growth habits of flowering cherries, but you can also consider a fruiting cherry. The blossom isn’t as spectacular, but the bonus of growing your own cherries is an option worth weighing up.

A Liriodendron tulipifera provides magnificent shade in Washbourne Gardens, Richmond.

Evergreen shade trees tend not to change through the seasons and, apart from flowers and sometimes berries, they will offer a very similar look year-round. If you are wanting to use your shade tree as a year-round screen to offer privacy, an evergreen tree will be a better option. A lot of the larger growing native trees, such as the pūriri, karaka, pōhutukawa, and tītoki, make spectacular shade trees, but in a town section, these will usually grow too big for the space available.

There are some good evergreen trees for smaller and town sections. Leptospermum Copper Sheen forms a good shade tree when its lower limbs are pruned. It has a lovely weeping habit, with its coppery-burgundy red foliage making it an attractive tree. It also becomes covered in a mass of white flowers in summer. This tree is very fast-growing, which makes it a good option for quickly establishing privacy. It responds well to trimming and can also be grown as a hedge.

Some michelia varieties form lovely shade trees. I say “some” because there are varieties that simply don’t grow large enough, and their habit is shrubby. However, the dolstopa variety and its hybrids form good evergreen trees. These varieties will form a trunk with a rounded head of branches and foliage that will offer good shade from the hot summer sun. A real feature of michelia is an amazing display of highly fragrant, white flowers in the late winter and early spring.

So, if you are feeling the summer heat, consider a good spot to plant a suitable shade tree.

For more gardening information, visit www.springvalegardencentre.co.nz.

Gareth Carter is general manager of Springvale Garden Centre.