Peter Matthews standing beneath the dahlia Imperialis in his Undercliff garden. Picture by Peter Boam.
GARDENINGAT LEAST two continents 'collide', in Peter Matthews’ garden.
He has an uncommon collection from around the world merrily thriving in that micro-climate that is the Undercliff.
I was introduced to Pete by chainsaw artist Paul Sivell, who chops up some of the trees that make their way to Pete’s woodyard. He especially wanted me to see dahlia Imperialis, which as the name suggests, is an imposing plant.
But, nestling nearby, was an unassuming sapling with leaves like a willow and a similar liking for wet conditions — acacia elongata, otherwise known as swamp wattle.
Its ball-shaped flowers have the distinctive perfume of mimosa and this acacia is a tad more tolerant to frost, surviving, as it does, down to -7C.
But the particular attribute that suits Pete’s Niton garden, which slopes down toward the Channel, is its resistance to salt-spray.
The tree hails from a coastal ribbon in New South Wales, Australia, but it can be successfully grown from its rock-hard seed in temperate areas all over, including Niton.
Many acacia, which are members of the mimosa family, are after-fire colonists (like elongata) and need that heat treatment to germinate. Some need to have boiling water poured on them and be left to stand overnight until they swell, some need just a minute’s immersion but a few tropical species are killed by hot water.
One ubiquitous substitute is scarification — reducing in thickness the seed’s hard outer covering between two sheets of sandpaper.
The joy of elongata and, of mimosa in general, is that they are fast-growing trees and within a couple of years you will have a sweet-smelling specimen.
The uncommon giant dahlia next to the swamp wattle is also easy to raise from seed but it only has a couple of similarities to the good old dahlia we know.
The swamp wattle (as it name may suggest) likes it wet, especially in earlier life, while, as we all know, dahlias tend to rot in those conditions.
There is obviously just enough water for the acacia and the sloping locale is clearly free-draining enough for the dahlia, which has been there five years now, and survives despite being left in the ground even during the fierce frosts and snow of the last two winters.
Last year’s early snow meant Pete’s giant tree dahlia did not flower and it was a particular treat that this mild autumn has coaxed it into bloom.
The flowers of this uncommon plant are borne on towering bamboo-like stems and for that reason are suitable for only sheltered, sunny, locations, like Pete’s patch.
Pete’s plant survives with only minimal support because it faces only wind from the south, its back sheltered by the Undercliff, but if you do decide to give this striking dahlia a try, it should be staked and supported every couple of feet of its height.
The tried and tested method of support is strips of nylon tights which are strong but also not dense enough to trap water and encourage rot.
Native to South America, the tree dahlia is becoming increasingly popular among gardeners in the southern and western United States, and even grows wild in parts of Hawaii, but in this country, perhaps because it does not suit all gardens, it remains uncommon.
Pete travelled to Ashington in West Sussex to the Big Plants nursery to seek out a plant among the gingkos and gnarled olives for which it made its name, but dahlia Imperialis can easily be grown from seed.
It averages between ten and 15 feet in height (though some report plants as high as 30 feet), the tree dahlia blooms in autumn with pink, lavender or white flowers up to seven inches across.
They thrive in sunlight. Full sun is best, although less is acceptable.
Soil for dahlias should be rich and moist but can range from sandy loam to slightly clay. Drainage is extremely important, as dahlias are sensitive to both too much, and too little, water.
Tree dahlias differ from their smaller cousins in that their tubers need to be planted up to 1ft deep and, if they are mulched heavily should survive Island winters.
What will not survive is the stem which holds a lot of water. It shone out like a beacon in its native Mexico to hunters who called it the "water cane." But here that attribute means its cell structure is destroyed quickly by frosts.
I have been told that one of the few purveyors of tree dahlia seed is Chiltern Seeds, should you wish to give it a go.
Chiltern Seeds tells me that its supplier in Java has been able to send a limited amount of seed for 2012.
Therefore a packet of 12 of these microscopic seeds costs £2.76.
• Chiltern Seeds can be found at www.chilternseeds.co.uk