Golden mimosa

The Cootamundra wattle is a species of acacia from Australia, one of the most dramatic flowering trees, flowering from the end of December for two months. Seen on a bleak day in January, it looks a most improbable sight.

Its small puff-ball-type lemon-yellow flowers are held on long flower stems against blue-green ash-like leaves, much divided into small leaflets, almost ferny in appearance.

It looks exotic and it is exotic, and – like many exotic plants – not very hardy. It is regularly tipped by frost, but only damaged in a very severe winter like that of 2010. Even then, acacia plants in gardens along the east coast survived, but the frost was not as bad.

Named after a town in Australia, the botanical name of the Cootamundra wattle is Acacia baileyana. It is grown in areas of Mediterranean climate all over the world, but it can get by here too. It is a large bush or small tree with long arching branches and those evergreen divided leaves, which are very handsome in their own right.

There is a very pretty form that has purple-tinged young shoots called ‘Purpurea’ and this is probably more available than the ordinary green sort, though perhaps a bit less hardy. This is really only a plant for areas within a few kilometres of the coast, although it has flowered further inland. In colder areas, it can be grown in a pot and taken into a greenhouse for protection, or grown in a green house or large tunnel.

Widely known as florist’s mimosa, Acacia dealbata, the silver wattle, has delicate ferny evergreen leaves, which have a silvery back. Later to flower, in February, the tight, rounded flower buds begin to swell and, soon after, they open in a fluffy, bright yellow haze.

The individual flowers are very tiny but, massed together on slender stems, they create a remarkable sight. If not killed as a sapling, it makes a tree to six, even 10 metres and as wide as tall. It is very fast-growing but still does not flower until it is about three metres tall.

There are other acacias too, such as Acacia pravissima and Acacia armata. These are large shrubs, not as big as the other two, and therefore more suitable for greenhouse for growing, or easier to accommodate on a warm wall. They are about as hardy as the mimosa, not as hardy as the Cootamundra wattle, and usually need a very favoured position, or greenhouse growing. Both are a bit more shapeless but can be pruned to a tidier shape.

The magnificent Acacia melanoxylon, or blackwood acacia, is a large tree, very similar in appearance when mature to the evergreen holm oak. It has dark-green leaves of similar size, although the young shoots have the ferny foliage of its relatives. It carries lovely pale-yellow flowers in late winter, high up on the tree. This species is usually only seen in large gardens near the coast, in mild areas with good shelter and, if you can find a plant, this is a superb tree. Trees of 15m and more than a century old were killed in the 2010 frost.

Acacias are members of the pea family, and they like free-draining soil that is reasonably fertile, though not too rich, as that makes them soft and more prone to frost damage.

Acacias need good shelter and full sunshine to grow well and come into flower at a younger age. A danger with acacias is that they are rocked by gales and the roots break, causing the tree to lean over and usually eventually fail. But they are worth the risk. CL

Pruning lower limbs on garden trees

Have you ever noticed how, in a mature forest, the trees have tall stems free of branches? This is the same for broadleaved trees or conifers, and it comes about because the tree tops shade each other’s branches, effectively pruning them. Garden trees usually have more space and they spread to fill it, often taking too much space and spreading their branches over smaller plants, denying them light. This can be rectified by pruning trees with a bow saw, taking off the lower limbs to allow light to reach smaller plants that were being suppressed. This operation just mimics the natural process of the removal of trees’ lower branches. It is easy to do, but choose carefully the lower branches to be removed.

>> This week

Trees, shrub and roses

Any further planting of trees or shrubs needs to be done in the coming months and try to get it done as early as possible. Carefully remove grass or weeds growing over the root area of young trees and they will grow twice as fast. A circle of diameter 1.5mt should be kept weed-free and some compost applied.

Fruit, vegetables and herbs

Plant all sorts of fruit trees and bushes during good weather and stake them as necessary. Remove mummified apples or pears, as these are a source of brown rot spores that will soon be emitted onto the air. Spread compost over areas for digging in during the next few weeks, or just top-up “no-dig” beds with rotted compost.

Flowers

Before you do a spring clean of flower beds, have a look to see if any good flower seedlings have popped up. Lots of flower plants self-sow, sometimes too freely, but the new plants can come in handy for planting, or be potted for charity sales. If there are gaps, new perennial flowers can be chosen to suit those already present.

Lawn

If there are tree roots coming up through the lawn in places, simply by expanding the girth of the roots as they age, they can be removed by splitting back the sods along the line of the root, then cutting the roots with an axe, back-filling with soil and reinstating the sods, watering them and tapping down firmly with a spade.

Greenhouse and houseplants

Rotate house plants to give them a few days or a week in the sunnier windows, though be careful not to move between extremes. Shade-lovers, used to being in low light, can scorch in a morning of direct sunlight. Buy seeds and prepare for sowing in the coming weeks. Check that the propagator is working properly.