Sea Aster, Aster tripolium (a.k.a. Tripolium pannonicum)

Jeremy Bartlett's LET IT GROW blog Posted on by

At the end of September we spent another week in Wells-next-the-Sea in North Norfolk, staying in a holiday cottage not very far from the quay. Our stay coincided with the last week of warm summer weather and we spent every day walking or cycling, looking at flowers and insects.

Our day trips took us past several areas of salt marsh. Here, the Sea Lavender had more or less finished flowering, but the Sea Aster was still in bloom.

Sea Aster, Aster tripolium

Sea Aster, Aster tripolium, at Brancaster, North Norfolk, growing with Shrubby Seablite and Sea Purslane.

Sea Aster, Aster tripolium (a.k.a. Tripolium pannonicum), is a short-lived perennial that grows on salt marshes, on muddy sea-banks, tidal river banks and in brackish ditches. In the west of the British Isles, where the coast is rockier, it can be found growing on exposed sea cliffs and among rocks. Because of its adaptability, Sea Aster can be found around most of the coast of the British Isles. It is a halophyte – a plant that will grow happily in soils or waters containing high concentrations of salt. Like Danish Scurvygrass, Sea Aster has recently colonised the edges of roads that have been treated with salt, although to a much lesser extent.

Sea Aster has semi-succulent, strap-like leaves and stems. The plant is a member of the Daisy Family, the Asteraceae. It flowers from July to October and each flower head is a composite flower, made up of many individual, tiny flowers known as florets.

There are two varieties of Sea Aster in the British Isles, separated by their flower structure. Flowers of Aster tripolium var. tripolium have a central group of yellow disc florets surrounded by pale mauve or white ray florets, while Aster tripolium var. discoideus lacks the ray florets. My photograph above shows the rayless (discoideus) variety, which predominates in many parts of East Anglia, though the rayed form (shown in my photo at the end of this post and also here and here) is the commoner form in much of the British Isles.

Outside the British Isles, Sea Aster grows around most of the coasts of Northern Europe, north to North Norway (where it is rare), in Finland and south to Portugal and the Mediterranean. It occurs as far east as Japan, but it is an endangered plant in the Tokyo area, threatened by coastal development, encroachment of saline habitats by reed, and inappropriate management of flood defences. Because of this, Professor Noboru Kuramoto from Meiji University in Japan is investigating the distribution and ecology of Sea Aster in Britain and Japan, with the assistance of The Essex Field Club.

Sea Aster is edible, though I haven’t tried it yet. The leaves can be cooked or pickled and the BBC Food website has a recipe for Pan-fried Salmon with Aster tripolium and Scallop Broth, which sounds good, as do Sea Aster Fish Bake and the even simpler Buttered Sea Aster, on the Eatweeds website. The Galloway Wild Foods website suggests pickling Sea Aster in slightly sweetened white wine vinegar with herbs, such as Coriander leaves, Wild Thyme and green (unripe) Alexanders seeds. If you live near the coast, it is possible to forage for Sea Aster. You may be able to grow the plant in your garden as well. In his book “Around The World In 80 Plants” Stephen Barstow relates how managed to grow Sea Aster in his garden in Norway, in bed of sand and also in a bucket of fresh water.

Sea Aster flowers are attractive to butterflies such as the Red Admiral. But they are particularly associated with the Sea Aster Mining Bee, Colletes halophilus. In the UK, this charismatic insect is restricted to the coast of Southern and Eastern England, from the Humber Estuary down to Dorset, with most colonies on the East Anglia coast and the Thames Estuary. The bee emerges in August when Sea Aster is in full flower and flies until the end of September.

Although we were at the end of the flight period, we were able to see several female Sea Aster Mining Bees and we followed them as they flew from one flower head to another, wrapping their bodies around the Sea Aster flowers as they gathered pollen. We were also lucky enough to find a nest site, with lots of individual nest holes in a bank. However, we were too late in the season to witness a mating ball, where a female bee emerges from its nest hole and is surrounded by a cluster of males.

Sea Aster Mining Bee, Colletes halophilus

Sea Aster Mining Bee, Colletes halophilus, on (rayless) Sea Aster

Rayed form of Sea Aster

Sea Aster Mining Bee, Colletes halophilus, and (rayed) Sea Aster

The Raised Bed Is Dead… Long Live The Raised Bed

Jeremy Bartlett's LET IT GROW blog Posted on by

We spent early November altering our front garden and replacing the big raised bed we built in October 2013 with a larger, lower flower bed. In just over a week we moved tens of plants and around thirteen tonnes of soil. It was hard work but we are pleased with the end result.

New Raised Bed

The new raised bed, 27th November 2016

We built the original raised bed on top of concrete, as we didn’t have the funds to break up the drive. In spite of this, the bed was a success and after a year the plants were thriving. After three years the plants growing in it, including an Olive tree, a Salvia ‘Hotlips’, a Broom, a Rosemary bush, Lavender, Mexican Fleabane (Erigeron karvinskianus) and a Giant Feather Grass (Stipa gigantea), had knitted together to form a small patch of Mediterranean scrub. When I watered in hot dry spells in the summer, the scented shrubs released delicious wafts of perfume and reminded me of holidays in Corsica, Majorca, Provence and Greece.

So why did we decide to replace the raised bed? There were several reasons, including:

  1. The bulbs I had planted in the raised bed didn’t do very well. The daffodils which looked so good in the first spring were soon crowded out by the growth of the shrubs and the  tulips, Anemone blanda and white Muscari didn’t have enough moisture to thrive.
  2. We wanted to water as little as possible. The new bed is lower and will allow plant roots to reach far down into the sub-soil to gather water and nutrients.
  3. The double red Midland Hawthorn trees on our road (Crataegus laevigata ‘Paul’s Scarlet’) are lovely but they are ninety years old and trees of similar age on nearby roads have been condemned by Norwich City Council and are in the process of being removed. We wanted to plant a medium sized tree in our front garden as an eventual replacement for the street trees at the front of our house, but the raised bed wasn’t deep enough to do this.
  4. We wanted more space. The raised bed had a wide slab path around its perimeter, which we wanted to replace with a bigger growing area.

Key to our plans was hiring a contractor to break up the concrete. In April 2016 I asked my friend Sue Bell, who is a garden designer, for a recommendation and she suggested Ian Cooper of IFC Landscapes Ltd. We arranged for the work to be done at the start of November, when the plants could be moved easily in a semi-dormant state and Ian would have time to do the job.

With a week to go until the work was done, we dug out the plants and moved them onto the patio in the back garden. The following day we moved at least five tonnes of soil from the raised bed to the front drive and dismantled the edges of the raised bed. We put the sleepers to one side and rescued the nail plates.

Ian ordered a skip to hold the broken up concrete, which arrived on the Monday. He and a workmate arrived the next day and broke up the concrete. They did a very neat job and lifted and cut the slabs so that most could be reused. By lunchtime they had finished and we loosened the sub-soil, put the sleepers back as an edging to the new bed and shovelled the raised bed soil back. We ordered another two and a half tonnes of soil to top up the new bed, using a mix of topsoil and compost from G. Nicholls of Oaks Farm, Great Plumstead (01603 720224).

On the Friday the soil was delivered onto the drive and we shovelled it into the new bed. In the late morning and afternoon we replanted, spacing plants further apart and using some of the slabs to make a stepping stone path through the middle of the bed.

In the following week we planted a large, bare-rooted Oriental Hawthorn tree, Crataegus laciniata (also known as C. orientalis). It will provide a similar effect to the double red Midland Hawthorns but will also have edible and ornamental fruits. The leaves should provide food for any Hawthorn-eating insects and some of these will provide food for the birds.

Other newcomers to the front garden include three plants I bought at Norfolk Plant Heritage‘s Hethersett Plant Fair in August: a Honey Bush (Melianthus major), with lovely glaucous foliage and a mouth-watering whiff of peanut butter when bruised, Coronilla valentina subsp. glauca ‘Citrina’, with scented lemon-yellow pea flowers from late winter to spring, and Angels’ Fishing Rods (Dierama igneum), with arching wands of reddish pink flowers in summer.

I’ve also planted some more bulbs (Tulipa saxatilis ‘Lilac Wonder’ and Crocus chrysanthus  ‘Blue Pearl’) for early spring colour. I couldn’t resist adding a couple of Giant Echiums (Echium pininana). I may need to cover them with fleece to protect them from frosts. I have some spare plants in an unheated greenhouse, along with some Geranium maderense plants that I raised from seed this summer (from Ventnor Botanic Garden). I will plant these out in spring.

Work in progress

Work in progress (5th November 2016): the old raised bed has been removed and the concrete is ready to break up.

The Raised Bed Is Dead… Long Live The Raised Bed.

Blackthorn, Prunus spinosa

Jeremy Bartlett's LET IT GROW blog Posted on by

The Blackthorn, or Sloe, Prunus spinosa, is one of my favourite wild shrubs. The plant produces masses of pretty white blossom in early spring and sloes, a key ingredient in Sloe Gin, in autumn.

Sloes

Sloes, late October 2016

In a week’s time I am going along to a gin tasting organised by No Fear Gardening, a new Norwich-based urban gardening club. My role is to talk about some of the ingredients used to flavour gin, including sloes. So I thought I could combine some homework with another post on my blog.

Blackthorn, Prunus spinosa, is in the Rosaceae, the Rose family. The genus Prunus can be split into six subgenera and three of these include several important fruit trees. Subgenus Amygdalus contains Almonds (Prunus dulcis) and Peaches (Prunus persica); subgenus Cerasus contains Cherries (Prunus avium and Prunus cerasus ) and subgenus Prunus includes Blackthorn and domesticated Plum trees (Prunus domestica). Blackthorn is believed to be one of the parents of the domesticated Plum, P. domestica, the other being the Cherry Plum, Prunus cerasifera.

The genus also contains the poisonous European Cherry Laurel (Prunus laurocerasus – subgenus Laurocerasus), the North American Sand Cherry (Prunus pumila – subgenus Lithocerasus) and European Bird Cherry (Prunus padus – subgenus Padus).

The sub-genera are distinguished by characteristics such as the arrangement of axillary buds and flowers, and the shape of the fruit.

Blackthorn grows in much of the British Isles, in open woodlands, hedgerows, as scrub on commons and rough ground and on screes and cliff-slopes. Although it normally grows as a shrub, it will grow as tall as 2.5 to 4 metres and will sometimes form a small tree (to ten metres tall).

When it is given the chance Blackthorn will spread sideways and outwards by suckers and a bush can be as wide as it is tall and often much wider. Indeed, I’ve spent many days keeping Blackthorn in check where it borders grasslands such as Alderford Common near Norwich. Without any maintenance these places would become solid thickets of Blackthorn. As well as providing a day of fresh air and exercise, clearance work in the autumn would often provide a good haul of sloes from the cut branches.

After a long, dark winter, Blackthorn blossom in the hedgerows is very welcome. Here in Norfolk, Blackthorn usually blossoms in March or April but the exact time varies depending on how warm a spring we have. Spring weather is very variable and a cold spell will often coincide with the onset of Blackthorn blossom, giving rise to the phrase “Blackthorn winter“. Cherry Plum (Prunus cerasifera) flowers even earlier than Blackthorn, with equally spectacular flowers.

Blackthorn blossom

Blackthorn in blossom

Blackthorn’s specific name spinosa refers to its sharp spines (which Cherry Plum lacks). These are very sharp and my bike tyres have suffered a number of punctures from Blackthorn spines, when hedges have been flail-mown and cuttings have been scattered on the road. The spines, which can reach over two inches (five centimetres) long, are also a hazard for anyone picking sloes or cutting Blackthorn scrub or hedges and they can easily penetrate leather gloves and even tractor tyres. It is quite common for part of a spine to break off after it has penetrated the skin and this can lead to inflammation, which can be serious. J. J. Kelly documented a number of cases in the 1966 paper “Blackthorn Inflammation” (on the Bone and Joint website) and other examples are given by H. Sharma and A. D. Meredith in a 2004 paper. The Netmums website gives some advice for children injured by Blackthorn.

Kneeling on a Blackthorn spine is a particularly bad idea (but is easy to do). A Blackthorn spine lodged in a joint can lead to a severe inflammation known as Plant Thorn Arthritis, Plant Thorn Synovitis or Thorn Arthritis. (Blackthorn isn’t the only species that can cause this.)

On a more cheery note, Blackthorn is an important plant for wildlife. Its flowers provide nectar for insects that emerge early in the spring, such as Small Tortoiseshell, Peacock and Brimstone butterflies, bees and hoverflies. The spines help to protect birds which nest in the branches and Blackthorn thickets can provide good habitat for Nightingales. In many parts of Europe, Shrikes (such as the Great Grey Shrike, Lanius excubitor), nest in Blackthorn bushes and impale a larder of food items on the thorns, which gives rise to their alternative name, the Butcher Bird.

Blackthorn is the food plant of the Brown Hairstreak and Black Hairstreak butterflies. Both species are quite restricted in range in the British Isles and the Black Hairstreak in particular prefers dense stands of mature blackthorn. A number of moth caterpillars also feed on Blackthorn. The Clouded Silver (Lomographa temerata), Green-brindled Crescent (Allophyes oxyacanthae) and Dark Dagger (Acronicta tridens) will also feed on other shrubs, such as Hawthorn, but the Sloe Carpet (Aleucis distinctata) is restricted to Blackthorn.

Blackthorn is easy to grow, though it is susceptible to Silver Leaf Disease, caused by the fungus Chondrostereum purpureum. (See my post “Winter Fungi” from 2012 for pictures.)  In the countryside Blackthorn is normally cut in the winter, but where Silver Leaf is a problem, you should only prune in dry spells in summer. (This is usually advised for Prunus fruit trees, such as Plums, Cherries, Almonds and Peaches.) If you do grow Blackthorn, give it enough room to spread or be prepared to cut back its suckers.

You have to be brave to eat a raw sloe, the Blackthorn’s fruit, and if you do you will probably do it only once. Sloes are very astringent, though frost can reduce the astringency and the Plants for a Future website says “some people find they can enjoy it raw“. (Avoid the stones, as they may contain cyanide glycosides.) The leaves can be used as a tea subsitute and the flowers are edible. There are also several medicinal uses for the plant.

Blackthorn wood is very hard and is used for making walking sticks and clubs, such as the Irish shillelagh.

The best use of sloes is for making jellies, syrups, conserves or flavoured alcoholic drinks. Sloe Vodka is quite good but the best is Sloe Gin. This is good to drink after just three months, but improves with age and becomes smoother and richer the longer it is stored. To make sloe gin, put pricked, bashed or frozen sloes in a large jar or demijohn and add sugar and gin (a cheap brand will do). There are numerous recipes, including these by River Cottage’s John Wright and on the BBC Food website and Very Berry Handmade website.

There are some great photographs of Blackthorn on the internet, such as on the Sulgrave Village and Wildscreen Arkive websites.