Observed during May 2008
2/5/2008
Climbing skyward this May weekend
Holboellia latifolia is a fellow member of the family Lardizabalaceae along with the previously described Akebia trifoliata. The plant driving itself upwards into the light on the Chinese Hillside was collected in Nepal in 1992 by members of the Edinburgh Makalu Expedition. In the wild, it is found growing in the Arun Valley at 2,750 metres through laurel forest.
The evergreen leaves are composed of varying numbers of leaflets, to a maximum of seven. Fresh growth is delicately translucent and slightly tinted bronze to protect from the higher-altitude UV rays of the sun in the Himalaya region. Our specimen reaches eight metres to the top of the supporting canopy.
Separate male and female flowers appear from nodes on the stems of all ages - deep in shade on the oldest wood to canopy top in bright sunshine. The six fleshy sepals are a mauve to purple shade; the male and female flowers are produced separately but mixed in the clusters. The male flowers are slightly smaller in cross section than the female. Both give off a heavy scent. The six free anthers produce copious amounts of white pollen.
6/5/2008
A celebration of the genus Rhododendron
The International Rhododendron Conference is taking place from 7 - 11 May 2008 at the Garden. The Royal Botanic Garden Edinburgh grows and has long been involved with the cultivation, research, classification and nomenclature of the genus Rhododendron. This is a group of plants that has an enthusiastic following, both professionally and through the garden centre trade as a plant to grow in the home garden.
The following hardy species are native to the Himalayan region where the most diverse examples of the genus grow. Collected through the centuries by dedicated plantsmen, these have enriched our garden flora with magnificent specimens.
They are now valued for reasons other than aesthetics as climate and land use change has played a part in their habitat loss. Growing within gardens throughout Scotland is well documented genetic material that can be used to reintroduce species into the wild.
- Rhododendron campylocarpum (see above) with Joseph Rock's collection number 1A is growing near Inverleith House. The delicate clear yellow flowers are held in a terminal cluster above the evergreen rounded leaves.
- R. rigidum ssp. triflorum (seen above): a much later introduction by Rock; collection number 11288, collected at 3,050 metres in the hills around Lijiang, Yunnan Province, China.
- R. augustinii ssp. augustinii: a Wilson collection from Sichuan, China with light blue flowers, dominant mottling on the upper petal and prominent ungainly flower parts.
- R. fortunei ssp. fortunei: the new growth shoots up in a spear, shedding protective red bracts as the leaves expand. Older wood is covered in large pink fragrant blooms.
But you cannot just garden with rhododendrons. Take a moment to appreciate the honey-laden scent given off by the flowers of Euphorbia mellifera as you enter by the North Gate.
9/5/2008
Two hybrid lilacs that differ in stature
These deciduous shrubs come into their own during May, covered in evocatively scented terminal panicles. Both of these hybrids have purple flowers and are shades similar, in fact indistinguishable, from each other. They are produced on the previous year's growth. Once flower colour has faded, cut these out to allow vigour to be put into vegetative growth, not seed pod production. A very therapeutic job with a pair of sharp secateurs that also tidies the plant up.
Syringa x chinensis (laciniata x vulgaris), pictured above: a weak open-growing, multi-stemmed small tree producing light green foliage; 3.5 metres tall by 2.5 metres spread. The buds pop open to reveal four perfect petals and yellow anther tips. It is commonly called the Rouen lilac as it was raised at the botanic garden in this, the capital city of the Normandy Region of France.
Syringa x persica (afghanica x laciniata)
A much more compact plant ideally suited for the smaller garden. Long grown in ancient Persia, the Persian lilac is an old hybrid that deserves to be widely cultivated. Reaches a maximum of two metres in a lax, twiggy habit.
13/5/2008
One of many reasons to visit Logan Botanic Garden
With a long weekend approaching, take a tent or book yourself some accommodation on the Mull of Galloway. Logan Botanic Garden grows a wealth of more unusual plants. Of special interest is Michelia yunnanensis, a member of the Magnoliaceae native to China.
At Edinburgh, we grow plants introduced through Kunming Institute of Botany in the Temperate House. These plants are much smaller and this is a good illustration of the climatic difference between the east coast and more sheltered areas on the west coast of Scotland. Several plants can be seen at Logan, in the Castle Woodland and within the Walled Garden. These are multi-stemmed plants growing to 2.7 metres and regularly producing fertile seed which is being grown on. 
Michelia yunnanensis is an evergreen with thick, glossy leathery leaves and a slight covering of brown indumentum on the reverse, set alternately in a spiral on the stem.
The flowers are borne singly and sit solitary in the leaf axils on a short, brown felted stalk. These are prized for their scent in China where street sellers tempt young girls to buy them as button holes for evening wear.
The flowers are Initially enclosed in a brown felted protective bract. This peels apart in two halves to reveal the tightly packed white petals and expands to reveal the mass of anthers and prominent green gynoecium. This female part of the floral structure is thrusted out prominently on a short stalk. The reflexed parts that cover it ensure its place in the family Magnoliaceae, resembling a Magnolia seed pod in miniature.
16/5/08
Star quality
This month sees Corokia cotoneaster covered in small yellow star shaped flowers. In bud, they are cardboard brown, expanding to allow the five linear petals to spread flat revealing an orange hue where the floral structure resides. A slight coconut fragrance can be detected on warmer days.
Planted to the north of the Front Range Glasshouses, it is a mass of twiggy, intertwining growth that forms an impenetrable barrier. This no-prune evergreen shrub should be allowed to develop its own form and stature as it amasses vegetative growth. Young leaves resemble a table tennis bat of fresh green, with a distinctive white reverse. A central mid rib runs the length of the stalk and leaf, becoming defined with maturity.
Nearby is a younger plant grown from seed collected near Wellington on North Island New Zealand. Corokia cotoneaster is member of the family Argophyllaceae.
20/5/08
Caught on the breeze like a prayer flag
Meconopsis punicea is guaranteed to attract interest with its tissue-thin petals of bright red showing each and every crease as they grow. The head is supported on a stem to 700mm, so thin that it is surprising it will bear any weight at all. This is covered in short brown hairs which are more noticeable as it kinks over with the weight of the single flower bud.
The four petals drop down to 110mm in length and then, as the head is caught in the breeze, fly open like prayer flags hanging on the mountainsides. Looking inside the petals, the inner darkens black at the well concealing the flattened and lobed stigma, also red in colour.
Multiple purple anthers are held tight until the petals drop and then gain a life of their own. Springing out from the embryo chamber they ripen later than the stigma.
In the wild, Meconopsis punicea is found growing on mountain passes at 3,600m near Hanghong and the Kangali Pass in Sichuan Province, China, where seeds will drop around the short lived perennial clumps. In cultivation it is unusual for the plant to survive for the following year once flowering has occurred.
30/5/2008
Compost tea
Much loved by bees, Symphytum officinale spreads throughout Europe and S.W. Asia.
Preferring moist soil in shaded conditions, the plants will colonise as a rampant long lived herbaceous groundcover. They also produce good growth in sun; just ensure the soil is deep and moist.
Flowers blue purple with a bulbous rounded tube of petals, this falls leaving a white needle like style, menacingly protective of the plant. In reality these will cause no damage being soft to the touch.
Clumping up and regenerating from the rootstock, a vigorous grower to 1 metre plus. Choose the planting position with care. The stems are covered in a sheen of white hairs, running a finger over these feels like the back of your neck after a short back and sides haircut.
Long pointed leaves are also covered in minute hairs. It is these leaves that have a high nutrient value when used as a teabag infusion in water to produce a concentrate liquid feed. Collect the leaves to soak in a water permeable bag, suspended in a barrel or bucket of water. After about 10 days a black concentrate will form. By diluting this, 1:10 - 1:15 a potassium rich liquid feed is obtained. The sodden mass of putrid leaves can be added to the compost heap. At all times the container should be lidded, this helps contain the smell and deter flies.
For previous years' highlights during this month, see the May Garden Highlights Archive page.