The country rises from close to sea level, in the tropical grasslands of the Terai, to a majestic 29,000 feet, at the summit of Everest, creating hundreds of micro-climates that support a staggering diversity of flora. Nepal was the source of many plants and flowers in gardens the world over. Wild orchids bloom abundantly on trees and cliffs while tiny gentians and violets create fine tapestries underfoot.

No matter how beautiful these smaller blooms might be, though, nothing can measure up to the rhododendron - Nepal's national flower - at its best.

An enthusiast could feasibly spend five months each year in pursuit of the rhododendron in the country. From one to the other, the flowers open in succession, as the altitude becomes greater. A few bloom in Kathmandu early in the year, but those trees are puny compared with those that grow higher up. Phulchoki, in Kathmandu's Godavari district, might see its first rhododendron flowers as early as February, but the optimum time is usually mid-March. The last of the season are generally found in June, but you'd have to trek for several days to reach them.

Rhododendrons belong to a huge family, with more than 1,000 members, including what gardeners still like to call azaleas. They are said to grow wild in most places except Africa and South America. The name derives from the Greek words (rose) and (tree).

Introduced to Europe in the 18th century, the flower soared in popularity. By the early 20th century, many species were being collected for private gardens and at the end of it, hybridisers (particularly in North America and Germany) were producing ever more exotic varieties to meet the insatiable demand for novelty. The rhododendron's popularity is easily explained: the flowers are gorgeous and almost infinitely varied. What at first inspection seems to be one big flower is actually a cluster of up to 20 separate blossoms on a single stem, like a ready-made bouquet.

Shrubby types grow relatively slowly, reaching only about 1.2 metres after 10 to 20 years. They flourish in a wide range of environments, from alpine to tropical and, if you find the right type for your altitude and climate, a rhododendron will thrive with minimal attention, provided the soil is acidic.

Nepal's , to give it its full botanical name, is at its most magnificent between altitudes of 5,000 and 12,000 feet. Climb to about 6,500 feet and you will reach forests with trees bearing shell-pink and white flowers besides the red.

Local tribes use the flower in religious rituals and the petals are eaten, although received wisdom suggests the rhododendron is poisonous. Its slightly bitter flavour is an acquired taste, whatever the truth. Nectar can be sucked from the flower, but locals urge caution as too much can make you feel nauseous. The wood of the tree is favoured for making charcoal and while juice extracted from the bark is used as a cough remedy.

Travel far enough up the Kathmandu Valley and you might find the flowers have another use.

During our long crawl towards the capital - Kathmandu lies at an altitude 4,600 feet - we find ourselves in a land that is bleak and bare in comparison to the rich black soil and healthy-looking leaves of the potato terraces of lower altitudes. Almost at the highest point of the road, we round a final hairpin bend and here, on an otherwise bare hilltop, a mound of rhododendron blooms dwarfs a simple wooden hut.

Human habitation seems to have ended far below and the outskirts of the city are still well ahead - yet the vibrant crimson of the petals is almost overwhelmed by the colours adorning a group of women seated on the ground around the heap.

The Nepalese love bright colours and these women seem quite unselfconscious bedecked in dazzling purples, emerald greens, scarlets and oranges as they skilfully and quickly strip out the white stamens at the centre of each flower and stack up the petals.

Clearly this is women's work. A few men stand around idle, but it turns out they gathered the flowers the previous day and are resting before beginning the next stage of the process.

The hut holds an enormous vat in which the separated petals are boiled with water and sugar until they soften into a thick, pink syrup. The resulting cordial is filtered into recycled plastic water bottles and sold in the city, to be diluted as a summer thirst quencher. Other batches are prepared without sugar and drunk with local whisky. Like all Nepalese, these people are truly hospitable and I am persuaded to sample this unexpected brew. A man pours a little of the cranberry-coloured liquid into a mug and hands it to me. I sip cautiously; it's too sweet for my taste, but I appreciate the strong fruity flavour.

Back in Kathmandu, Nepalese friends say they enjoy the drink in hot weather, but admit they never realised it was made from rhododendron blossoms. It seems the country's national flower gets under the skin, even without many Nepalis noticing. To see its blossoms, though, is something you'll never forget.