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Planting Under Established Eucalypts
Although originally intended for a Canberra audience, the ideas described in this article have wider application. It may be necessary to substitute different species to those mentioned but the principles outlined here should succeed in a range of climates.
One of the questions frequently asked by people new to native gardens is: what will grow well under a mature eucalypt where there is competition for soil, water, nutrients and light. This article explores some ideas for such a situation. It's important to remember we're talking about an established tree here, that is, one that is well grown AND there before the garden bed. Some of the ideas fall into the 'How to' category and involve gardening techniques, others are 'What to' suggestions for selecting plants.
One answer of course is not to plant at all. It's perfectly possible to develop such an area into an attractive garden space by making an open clearing carpeted with mulch and gravel, adding a seat and a birdbath and/or some pots or a small 'wet patch'.
If however you want to plant a garden AND there is a metre plus trunk height before the first branches. The fine feeder roots will be out at the drip-line, the place at the edge of the canopy, where the water drips off the pointed tip of the "traditional" leaf. This means the area under the canopy, that is, from the drip-line in to the trunk, will have less root competition. This is where it is possible to find pockets of soil for growing individual plants. If, however, your garden already has a large bare patch under a eucalypt that is a prime candidate for making a new bed.
Extend a nearby bed to take in any bald patch outside its border. Things will look a lot better immediately. Perhaps this means all the lawn is gone? No matter - think of the effort you will save and the decrease in the water bill. You could add some soil or compost but do not under any circumstances raise the soil level around an established tree more than 5 cm. Raising the level more than this changes the drainage, and, decreases the amount of air and water reaching the old ground level, thereby upsetting the tree's feeding regime, and leading to disease and possible death.
Mulch is another matter, as it falls naturally in summer, when the tree decides fewer leaves mean less water used. Mulch cools the roots in summer, provides some nutrients and blankets the soil against wind and water erosion.
Another trick is to plant right close to the trunk to take advantage of the water collected on the branches and funnelled back to the trunk. This is a good spot for plants that appreciate shade, dappled overhead cover, or need light frost protection. Examples are waratahs and boronias. Try Boronia 'Telopea Valley Star', B.'Lome Pride', B.'Sunset Serenade'. There would not be enough water for B.megastigma or B.heterophylla forms.
Now what type of plants? Given the small pockets of soil it is probably a good idea to stick to smallish plants of the size sold by the Society, and let them find their own way through the competition. Advanced specimens are probably more difficult to establish in this situation.
Pea family plants are useful as they provide some of their own food needs, through nitrogen fixing nodules on their roots. sennas, the cassias that were, with yellow-golden cup flowers in late spring, are a traditional item. In Canberra use Senna odorata with larger compound bright green leaves and S.artemisoides, which has silvery-grey to grey-green leaves, with much finer leaflets.
Any of the smaller 'egg and bacon' peas also work well, starting with prostrate platylobiums and oxylobiums. Think of the banks of orange and golden peas mixed with boulders at the base of Eucalyptus pauciflora in the Brindabellas. In Gudgenby, you have a light ground cover of Lotus australis and the smaller form of Mirbelia oxylobioides. There's davesias, Pultenaea cunninghamii, P.'Glenluce Gold', P.'Pyalong Pink', nearer home P.subspicata, Dillwynia retorta, Dillwynia sericea and many more.
Another suggestion would be to try Brachysema praemorsum prostrate forms, including the bronze leaved 'Brown Butterflies'. Brachysema minor should do well under trees that have a lighter canopy letting in some periods of full sun. Try too the various forms of Hardenbergia violacea which must have some sun to flower well. Hardenbergia 'Mini Ha Ha' has smaller leaves and shorter intemodes, but still reaches 60 x 150cm. A note of caution, H.' White Wanderer', H. Happy Wanderer', and H. 'Free'n'Easy' are extremely vigorous and have the potential to smother small plants. Frost does cut them back but not enough!
Don't forget wattles belong to the pea family too. If you have a large bed, you could try some of the big prostrate forms, but these will need some periods of sun too. A smaller prostrate is Acacia cardiophylla 'Kuranga Gold'. Acacia buxifolia does well, but really needs lighter soil, or soil with rocky bits mixed in to do really well. The local A.pycnantha makes a lightweight tree, and loves dry hillsides. The plants needing some full sun equate to those on the borders between the forest and the roads and clearings.
Take a leaf from nature and think of the dry hillsides you have seen. (We'll stick to dry, as Canberra is running out of water). What grows well there? The Victorian goldfields give you Correa reflexa and Grevillea alpina. Canberra gives you Bracteantha viscosa, Acacia giinnii, Grevillea lanigera, Hakea microcarpa, Gompholobium huegelii, Persoonia chamaepitys and Cryptandra amara where there is some full sun. In the Southern Highlands you have Banksia spinulosa forms happily co-existing with eucalypts. From the damper Brindabellas comes Grevillea diminuta. Jacksonia scoparia is a widespread small, lightweight tree with yellow, scented pea flowers. The silver leaved, orange flowered form of Grevillea arenaria has proved hardy locally, but is more of a sunny clearing plant.
Other plants that like dry conditions and full sun...... Calytrix springs immediately to mind. It comes in shades of dark through light pink to white, from utterly prostrate through procumbent to upright, and often has colourful calyces that remain on the plant after flowering. Philotheca (Eriostemon) myoporoides can also be very tough. Before the road was upgraded, plants grew on a hilltop at Mount Hope, halfway to Cobar.
If a plant needs the well drained spot you don't have, then plant it next to a large shrub, which will soak up most of the water. Prostanthera phylicifolia is such a plant, possibly Prostanthera gilesii from the side of Mt. Canobalas at Orange, while P.scutellarioides certainly should fit right in.
|Leucochrysum albicans ssp. albicans
Herby stuff with tuberous or swollen roots should do well too. Try the varied Chrysocephalum apiculatum and C.semipapposum forms. Leucochrysum albicans, Bulbine bulbosa and Rhodanthe anthemoides should make good border plants for dry conditions. Wahlenbergia stricta would mix well with both yellow and white daisies, as would Dampiera stricta, available in both white several shades of blue. Thelionema caespitosum with cream or blue flowers is a 'tufty' that can flower in spring with increased moisture and die back over summer. Patersonia, flowering over summer, is a small 'tufty' from very well drained areas that is well worth trying.
'Small' is another survival tactic, for 'small' uses fewer resources. If the bed borders a lawn, use Brachyscome multifida forms, Scaevola albida forms and further dampieras to soak up the over-spray. If you are willing to add more water, a wider range of plants can be grown. Too much water and there's no need for the drip-line's services. You'll be feeding a eucalypt as well as the garden bed. Add some of the understorey from the Brindabellas, such as Olearia erubescens. If only a little water is available, the various westringias would do well. Try some of the variegated forms e.g. Westringia 'Smokie', W.'Morning Light', W.'Lavender and Lace', to lighten the potential shade. W.glabra compact with nice pinkish flowers and green leaves, looks healthier than the smaller, darker leaved forms.
Another approach is to use large growing hybrid grevilleas, which should be vigorous enough to grow, albeit to less than quoted size, in competition with eucalypt roots, although the reduced sunlight will probably lead to reduced flowering.
Several of the Society's members have established very attractive and successful gardens under and around large eucalypts. Morrie Duggan, for example, has a delightfully shady garden at Flynn where he grows some wonderful plants, including the lovely Dodonaea sinuolata that has soft, ferny leaves and showy pink seed cases for long periods of the year. At Bywong, Hilary and John Merritt have a collection of prostantheras and westringias that thrive in the dappled light under a variety of eucalypts, and some long-flowering showy Phebalium stenophyllum in deep leaf litter under Eucalyptus cinerea. Barbara Daly in Cook has a lot of success with prostantheras and thryptomenes. Lyndal and Tom Thorburn have many eremophilas interplanted in their hillside at Greenleigh in Queanbeyan, while Glenn Pure in Kambah has Brachysema lanceolatum under his eucalypts. Carmel Statham in Fisher has Myoporum, prostantheras, Correa glabra var. turnbullii, Acacia leucoclada and Darwinia citriodora under her trees.
The real secret to gardening under established trees is to think of it not as a challenge but as an opportunity. Draw lessons from natural woodlands and other gardens and experiment with some of the plants mentioned above.
From the Newsletter of the Australian Native Plants Society (Canberra), December 2003.
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Australian Plants online - June 2004
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