Sweet pea bushes

As summer moves on, and the raspberries finally stop fruiting it is time to clean out the bed they grow in, to remove the old spent canes and to tie up the new canes. Most raspberries, of course, fruit on wood they made the previous year, so it is important to remember to keep the supply of new wood replenished, and to remove the old wood.
I do try to keep an eye on the canes during the earlier part of the growing season as the job of training the new stems is a lot easier while they are still pliable.
While I was down in the raspberry patch, I had a wander along the back of the shrubbery that I wrote of last week. It is about three meters wide, with a number of large natives, and a few deciduous shrubs, including a couple of the more unusual Hydrangea species and a giant mock-orange, Philadelphus. I have been cogitating about how I am going to change this garden, more or less deciding on replacing the under storey with some native ferns, so I was taking a mental stock take of the existing planting when I came across a Polygala growing against the fence. I was a bit puzzled at first as I did not recall planting it, then I remembered that it was already here when we arrived, planted by the previous owners. I have not noticed it for a while, as it is so shaded that it does not flower very well now.
I had a chuckle because a work mate, Paul, was talking about Polygalas the other day, saying how valuable they were as a no-fuss shrub – and he is absolutely right, they are very useful shrubs. I told him I did not have any in my garden.
There are many, many species of Polygala, found scattered over most of the earth except our little corner of the world. The only one commonly grown in gardens is the South African species, P. myrtifolia. This has bright green leaves, and has tidy growth habits meaning it has become deservedly popular in New Zealand gardens. The usual form you will find is “Grandiflora”, which has larger flowers that the type species.
These flowers are reddish-purple and pea shaped, although the plant is not actually a legume. The flowers are held in clusters at the end of the branches, with a pronounced flush in the late winter/early spring, but also intermittently throughout the year.
There are other forms around too, with “Dazzler” being perhaps the best known. It has more compact growth and slightly more glaucous leaves. There is a smaller form again, “Liddle Dwarf,” grown by Liddle Wonder nurseries in Waikanae. It is said to only grow to 80 cm so it should be a great addition to the very small flowering shrubs available, especially with its extended flowering season.
There is a bit of a drawback to these plants – the colour of the flowers. The purple shade is strident and it is hard to find flowers that will tone in with them. Perhaps the best bet is plants that flower in a similar colour range, or perhaps in very light shades.
Plants do not get as popular as these have without a reason, and the main reason is the ease with which these shrubs grow. They will flourish in any good soil in full sun, and will even do well in poor soils, provided they are well-drained.
They benefit from as light pruning when planted and an annual trimming will keep them looking nicely shaped.
Most of you will have probably grown one or another of these, but few will realise that some forms of this species have become a pest in the north, in yet another example of a foreign plant succeeding altogether too well in its new environment. It seems that the problem stems from seedlings establishing themselves sin coastal areas of western Auckland. The forms that most nurseries offer are sterile and, as such, will not cause a problem out in the wild.
This plant is often known as the sweet pea shrub – Paul calls it that – but to my mind that name belongs to another shrub Podalyria calyptara. This is another South African shrub but this one has altogether different growth habits. To start with, it has the most amazing silky grey foliage. The leaves themselves are greyish green but they are covered with tiny white hairs, giving a silvery sheen.
The flowers are equally surprising – pale pinkish mauve flowers about the size of sweet peas, very nicely scented and carried with abundance in the spring and summer. These are very useful cut flowers, lasting for weeks if properly cared for. They probably need slightly warmer conditions than the Polygala varieties, and I suspect that they cannot cope with such strong frosts.
This is also a lot easier to mix in the garden as the subtle shades can be more easily accommodated. It grows to about two metres when happy.
Another Podalyria, the satin bush P. sericea, is also available in New Zealand. This also has silver leaves but is a lot smaller than the sweet pea bush, only reaching about 80 cm. the flowers are correspondingly smaller. The flowers are lilac rose and carried in large numbers in spring. They are followed by silvery seedpods.
And yes, they have escaped from the garden and are on watch lists in the north, so plant with caution, especially in coastal areas.
Another plant is sometimes called the sweet pea bush – the bright blue Psoralea pinnata, more commonly called blue broom. This has needle-like foliage and mainly flowers in spring. Commonly found in coastal areas, it is not so usually found inland as it will only cope with moderate frosts.
And, as I am sure you will have guessed, it has become a weed, this time on Great Barrier Island! Not so sweet after all.