Mimosa, Acacia dealbata

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Mimosa, Acacia dealbata

Our very mild late winter and spring has suited tender plants, such as Mimosa, Acacia dealbata. There are several Mimosa trees in Norwich and they have been flowering for weeks now, lighting up front gardens with the bright yellow puffs of their flowers. As I write, some of the flowers are beginning to turn brown with age, but from a distance the effect is still magnificent. Close up, the flowers have a delicious scent. The Fragantica website describes this as a “child-like, sweet, soft and hazy heliotrope-smelling note with sugar-spun tonalities”. Mary Keen describes the scent as the “smell of southern spring“.  They smell nice, anyway.

Acacia dealbata is a native of southeastern Australia (New South Wales, Victoria, Tasmania and the Australian Capital Territory). It was introduced into Southern France in 1820 and is now widely planted and naturalised in many parts of the world with a suitable climate, including other parts of Australia, the Mediterranean region from Portugal to Greece and Morocco to Israel, the Black Sea coast of Russia, Ukraine, California, Madagascar, South Africa, Zimbabwe, the highlands of southern India, south-western China and Chile. It can be a serious weed in New Zealand and parts of South Africa.

Mimosa is a member of the Fabaceae, the Pea family. Other English names include Silver Wattle and Blue Wattle. In its native land Acacia dealbata is a pioneer species that colonises after a bush fire. The roots have nitrogen-fixing bacteria in their nodules, and can bind together soils to prevent erosion. Mimosa grows rapidly to about 30 metres (100 feet) tall but seldom lives longer than thirty to forty years. In the UK, it is more likely to reach 8 – 12 metres (26 – 40 feet) tall and frost, rather than natural causes or fire, is likely to end its life.

In the UK, growing Mimosa is often a bit of a gamble and “probably not something to try out of doors north of the Trent“. It can survive brief cold spells down to -10°C, but it is officially given a hardiness rating of H3 by the RHS: Hardy in coastal and relatively mild parts of the UK (-5 to 1°C).  It would probably not survive a cold winter like 2009 and 2010, though most winters are now milder in the south of England.

Shrubs such as Leptospermum are equally tender but small enough to cover in the winter, whereas Mimosa can become too tall to wrap up against the chill. It is most likely to survive in a sunny, sheltered spot in well-drained soil. If cut down by frost, it may regrow as a multi-stemmed shrub. If you need to prune your Mimosa, follow the RHS instructions for Early flowering evergreen shrubs (pruning group 8) – prune after flowering.

Acacia dealbata subspecies ‘Subalpina’, which grows at higher altitudes, is a bit hardier than the wild type and said to be worth seeking out: at the time of writing it is stocked by Shoot. James Wong mentions a related dwarf form, Acacia nanodealbata (sometimes spelt nono-dealbata). Anna McKane describes some other hardy (ish) Acacia species in her 1996 article in The Independent, “On the trail of hardy mimosas“.

Mimosa trees can be raised from semi-hardwood cuttings or from seed, though the seeds need to be treated with boiling water and then left to soak for a day. The boiling water mimics the heat of a fire that would trigger germination in the wild.

The Plants for a Future website tells us that Mimosa gum (which exudes from the trunk) is edible, and can be used as a substitute for gum arabic. The real thing comes from two close relatives: Senegalia senegal (Gum Acacia) and Vachellia seyal (Red Acacia).

Mimosa flowers are often sold by florists. The flowers are edible when cooked and according to Plants for a Future can be made into fritters, although the recipes I found when searching for “Acacia flower fritters” used the white flowers of the related Black Locust tree,  Robinia pseudoacacia.  Mimosa can be used as a dye plant, either for yellow (the flowers) or green (the seed pods).

Mimosa Salad sounds appetising, but no Mimosa was harmed (or used) in making it. A festive salad in the former USSR, its main ingredients are cheese, eggs, canned fish, onion, and mayonnaise. If boiled egg yolk is crumbled and scattered on its surface, it is said to resemble mimosa flowers scattered on snow.

Mimosa, Acacia dealbata

Mimosa against a blue March sky.

Why You Should Ditch Peat

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Large Heath butterfly

The Large Heath butterfly – a species that has seriously declined following destruction of peat bogs. (The plant in the background is Bilberry, Vaccinium myrtillus.)

This morning we walked to our local garden centre. It was good to stretch our legs, but the experience was rather disappointing. Like many such places, it has become more gift shop and cafe than a place to buy plants. The only Hollyhocks on sale were double-flowered and therefore useless to pollinators and the trays of mixed blowsy-flowered Primulas made me feel a little bilious. We came away empty handed (note 1).

Saddest of all were the huge piles of bags of compost by the entrance, most of which contained peat.

In the United Kingdom, the industrial scale extraction of peat has destroyed or damaged more than 95% of lowland bogs. In Ireland, the Irish Peatland Conservation Council (IPCC) estimate that 90% of its raised bogs have been lost (note 2). As the IPCC say: “Peat may be dirt cheap, but it costs the earth.”

Peat is composed of waterlogged, partially-decomposed plant material (including sphagnum moss and other acid-loving plants), which builds up in wetland habitats such as fens, bogs and moorland. The process is slow: about 1 millimetre of peat forms in a year, and deposits in the British Isles have gradually built up over 10,000 years. In contrast, average annual extraction from a peat bog removes 20cm (8 inches) of peat in a year, which represents 200 years of peat formation (note 3). It’s actually worse than that because bogs are drained before extraction takes place, to allow machinery to work on the site. This kills off large tracts of peat and its unique plant and animal community. Industrial scale peat extraction is no more sustainable than clear-felling rainforest to create palm oil plantations.

Peat bogs are wonderful places, full of interesting plants, including beauties such as Bog Asphodel and Grass of Parnassus, which I have previously written about. Insect life abounds there too, such as the Black Darter dragonfly and, pictured above, the Large Heath butterfly. More recently, we have realised that peat bogs are great carbon sinks, capturing carbon dioxide from the atmosphere. It has been estimated 5% of the carbon currently locked up in the UK’s peatlands is equivalent to the UK’s annual greenhouse gas emissions (note 4). Peat bogs also store vast amounts of water and slow its release into rivers, preventing catastrophic flooding (note 5).

Some three billion litres of peat are used every year in our gardens. We have known that harvesting peat is damaging and unsustainable for many years, but the majority of commercial composts still contain a large proportion of peat. Unless a bag of multi-purpose compost says it is peat free, it will contain peat. Some bags say that the peat doesn’t come from a SSSI (Site of Scientific Interest), but this is either because the extraction site is so degraded that it has no designation or if it comes from outside the United Kingdom, where the term SSSI isn’t used (note 6).

In December 2010 the British Government announced a plan to phase out the horticultural use of peat by gardeners by 2020. But as I write, peat extraction for gardening in the UK is still rising.

The following quote from Monty Don, which dates from March 2002, is still sadly true:

“Go to any garden centre and try and buy a non-peat based compost. It is certainly easier now than it was even five years ago, when you had more chance of scoring a bag of heroin over the counter at the local supermarket, but you still have to fight past the pallets of peat and peat-based composts to get to it.”

Alternatives to Peat

I stopped using peat in the 1980s.

For containers of shrubs and hardy perennials I use my home-made compost, which starts off as kitchen and garden waste. However, my own compost doesn’t rot at a high enough temperature to kill all weed seeds, so I use a commercial compost for the top inch or so of the pot, to stop light from triggering  germination of unwanted seedlings. (Peter Hill also suggests this in his February 2010 Guardian  article “Tips for a Peat Free Garden“.)

For raising seedlings and small plants, whether vegetables or wild flowers, I buy bags of peat-free compost.

The quality of composts can be variable, and I have learnt that some ones are better than others. Price can be an indicator, as you generally get what you pay for. I have had the occasional failure: about twenty years ago one (not cheap) brand of peat-free compost, whose formula has now changed, only gave me a crop of Common Inkcap fungi, rather than the potatoes I had hoped for.

If you’re switching to a peat-free compost, bear in mind that the compost may behave differently to a peat-based one. This is not necessarily a bad thing, but it’s best to check that plants really need watering. The surface of a coir or wood-chip based compost can dry out on the surface while the depths remain moist. Don’t rely on visual clues – poke a finger into the compost to check.

There is a lot of useful advice on peat-free composts online. One of the best articles I’ve found comes from the Telegraph just a couple days ago. There are also recommendations on the RHS and  Earth-Friendly Gardener websites. It includes some recommended brands. I’ve had success  New Horizon compost (a blend of coir, wood fibre and bark) and Fertile Fibre. The former is available in many garden centres, as well as DIY stores such as Homebase and Wickes. Buying online with home delivery makes sense if you don’t have a car, or a garden centre near where you live.

Peat is often used to lower soil pH, making it more suitable for growing lime-hating plants such as Blueberries and Rhododendrons. But peat-free ericaceous composts are available, including Ericaceous Wool Compost and Vital Earth Ericaceous Compost. I’ve had success growing Blueberries in a tub in a wool-based compost. On a larger scale, it is probably better to stop fighting nature and grow plants suited to your garden soil.

Notes

Note 1:  To be fair, they did have a smaller number of nice plants too, including some Cowslips and a couple of varieties of Lungwort.

Note 2: This loss has resulted from a combination of commercial peat extraction, turf cutting and forestry. See http://www.ipcc.ie/help-ipcc/be-a-peat-free-gardener/.

Note 3: Plantlife gives a higher figure: “Commercial extraction can remove over 500 years worth of ‘growth’ in a single year“.

Note 4: IUCN UK Peatland Programme (2011), Commission of Inquiry on Peatlands: Summary of Findings, October 2011. Quoted by Plantlife: https://www.plantlife.org.uk/uk/our-work/campaigning-change/why-we-need-to-keep-peat-in-the-ground-and-out-of-our-gardens.

Note 5: One inspiring story, reported in the Independent newspaper in January 2016, comes from Pickering in Yorkshire, which was flooded four times between 1999 and 2007. Rather than building an ugly and expensive flood wall in the town, local people, local councils, the Environment Agency, the Forestry Commission and DEFRA (the Department of the Environment, Food and Rural Affairs) worked together to slow water flow from surrounding moorland. The scheme worked well, the peat soaked up excess rainfall and the scheme cost only a tenth of building a flood wall.

Note 6: Even in Northern Ireland and the Isle of Man, the alternative term Area of Special Scientific Interest (ASSI) is used. Currently 32% of our peat comes from the UK, 60% from Ireland and 8% from Europe. (Plantlife: https://www.plantlife.org.uk/uk/our-work/campaigning-change/why-we-need-to-keep-peat-in-the-ground-and-out-of-our-gardens.)

Lungwort, Pulmonaria officinalis

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Lungwort, Pulmonaria officinalis

Lungwort, Pulmonaria officinalis. Growing at the base of an east-facing wall in a garden in Kelling, North Norfolk, early April 2018.

Spring has arrived all of a sudden, with record-breaking February temperatures in parts of Britain. While it has been lovely out in the sunshine, the unseasonal weather is distinctly unsettling, with our knowledge that the Earth is expected to experience more record-breaking temperatures this year (note 1).

One result of the extra warmth has been the early appearance of hibernating bumblebees, butterflies (Peacock, Small Tortoiseshell, Comma and Brimstone) and the emergence of some solitary bees. One of these has been Anthophora plumipes, the Hairy-footed Flower Bee, which feeds on spring flowers such as Primroses, ‘Bowles’ Mauve’ Wallflowers and Lungwort.

Lungwort, Pulmonaria officinalis, normally starts to flower in March and continues through to May.  It’s a slow-growing perennial plant and has characteristic white spots on its leaves. Like Oysterplant, it is a member of the family Boraginaceae. Unlike Oysterplant, you won’t find it on a beach but in a garden or naturalised in woods, scrub or on waste ground. Lungwort has purple flowers, which start off pink, like several other members of its family.

In the British Isles the plant is an introduction, but it occurs widely in the wild in continental Europe. The plant prefers fairly open shade, a reasonably moist but not waterlogged soil and not too much summer heat. It is hardy to UK hardiness zone H4 (-10ºC to -5ºC). Lungwort flowers lack scent, but bees still are able to find them, possibly (with the ability to see ultraviolet light) as “incandescent beacons, shining like lamps in the semi-shade” (note 2).

The article “Biological Flora of the British Isles: Pulmonaria officinalis” is well worth a read (note 3). It snappily describes the plant as a “distylous, perennial rosette hemicryptophyte“. Distylous means that the flowers come with long and short styles and stamens, rather like pin- and thrum-eyed Primroses. A hemicryptophyte is a plant whose perennating buds are at ground level, the aerial shoots dying down at the onset of unfavourable conditions (such as in the heat of summer).

Like the name Lungwort the scientific name, Pulmonaria, refers to the lungs (Latin Pulmoa) . This is because the plant’s spotty leaves were thought to resemble diseased, ulcerated lungs. The Doctrine of Signatures, used in folk medicine, drew upon the belief that if a natural object looked like a part of the body it could cure diseases that arose there (note 4). Other examples include Liverworts, Spleenwort, Eyebright and Toothwort. The specific name ‘officinalis‘ refers to Lungwort’s use in herbal medicine.

Lungwort leaves have a high mucilage content and have been used externally for the treatment of burns and eczema. Internally, the plant has been used to treat sore throats, as well as chest conditions such as coughs (sometimes in conjunction with Coltsfoot). Lungwort’s phytochemistry has only been investigated very recently (note 5).

Lungwort leaves are edible raw or cooked but the plants growing in my dry garden soil need all the leaves they can grow, just to survive, so I haven’t tried them. Besides, the plant doesn’t exactly have rave reviews on the Plants For A Future website. “A fairly bland flavour… an acceptable addition to mixed salads, though their mucilaginous and slightly hairy texture make them less acceptable when eaten on their own“. Cooked, the young leaves “make a palatable cooked vegetable, though we have found the texture to be somewhat slimy.”

I am not alone in recommending Pulmonaria officinalis and other Pulmonaria species as garden flowers: Lungwort was Plant of the Week in The Guardian in March 2017 and featured in The Telegraph in 2002. The RHS also offers advice on growing the plant. Different Pulmonaria flower colours and leaf shapes are available, as are plants with unspotted leaves. My own favourite remains Pulmonaria officinalis and I have fond memories of it growing in gardens in north-east Scotland.

Two other Lungworts grow wild in the British Isles, but are not common and I haven’t seen them (but see Update – May 2019, below). Both are native, unlike Pulmonaria officinalis.

Narrow-leaved Lungwort, Pulmonaria longifolia, grows in light shade in Hampshire, around the Solent and on the Isle of Wight, and in Dorset, near Poole Harbour. It has narrower, oval, bluish-green lightly spotted leaves and smaller, but “piercingly blue” flowers (note 2).

Unspotted or Suffolk Lungwort, Pulmonaria obscura, grows only twenty miles from home, but is confined to three privately-owned Suffolk woods, which are inaccessible by public transport and only seldom open to public visits. Its name comes from the lack of spots on its leaves, but as I haven’t seen it, I think that “Unspotted” is rather appropriate. The lovely NatureGate website has photographs of this lovely plant, which also grows in southern Finland.

Lungwort is also known by other English names, including Mary-spilt-the-Milk (note 6), Lady’s Milk-drops (from the spots on the leaves), Spotted Dog, Soldiers and Sailors, Jerusalem Sage, Bethlehem Sage and Jerusalem Cowslip. I wonder whether the “Jerusalem” and “Bethlehem” names come from the plant’s Easter flowering time, but I have so far been unable to find out.

Notes

Note 1: The article “Media reaction: The UK’s record-breaking winter heat in 2019” on the Carbon Brief website is well worth a read, and includes Met Office diagrams showing how great the maximum daily temperature anomalies have been.

Note 2: I recommend Peter Marren’s very enjoyable book “Chasing The Ghost – My Search For All the Wild Flowers of Britain” (Square Peg, London, 2018). It has some very vivid descriptions of Lungwort flowers, including Pulmonaria longifolia and P. obscura. He managed to see P. obscura in Suffolk, and found that is “not only attractive and grows in a lovely, wild location, but is also reasonably distinctive and not ‘obscure’ at all”.

Note 3: See Sofie Meeus, Rein Brys, Olivier Honnay and Hans Jacquemyn (1992) – “Biological Flora of the British Isles: Pulmonaria officinalis“.  Reprinted in the Journal of Ecology (2013), 101, 1353–1368.

Note 4: The Swiss physician Paracelsus was an important advocate of the Doctrine of Signatures and thought that “Nature marks each growth… according to its curative benefit“.

Note 5: See Krzyzanowska-Kowalczyk J, Pecio L, Moldoch J, Ludwiczuk A, Kowalczyk M. Novel (2018) –  “Phenolic Constituents of Pulmonaria officinalis L.”  Molecules. 2018;23(9):2277. Thanks to the United States National Center for Biotechnology Information for putting the article online.

Note 6: Richard Mabey (1996): “Flora Britannica“, Sinclair-Stevenson, London. Page 306.

Update – May 2019

I have now managed to see both Unspotted or Suffolk Lungwort, Pulmonaria obscura, and Narrow-leaved Lungwort, Pulmonaria longifolia. In early May I helped with a count of plants in two of the woods where Suffolk Lungwort grows, then in mid May I went to see Narrow-leaved Lungwort while staying on the Isle of Wight. Here are pictures, for comparison with our better known spotty friend:

Narrow-leaved Lungwort, Pulmonaria longifolia

Narrow-leaved Lungwort, Pulmonaria longifolia.

Unspotted or Suffolk Lungwort, Pulmonaria obscura

Unspotted or Suffolk Lungwort, Pulmonaria obscura