The tree collection is the backbone of the woodland garden and the chief glory of the various collections at Tregrehan. The garden was originally planted as an arboretum from the middle of the 19th century onwards. Then grew into a woodland garden with the understory filling in as the shade and shelter canopy developed. This is unusual especially in the westcountry as most valley gardens in Cornwall used the existing native canopy and natural topography to create their woodland microclimate.

By the 1st World War word had spread and WJ Bean and Jackson both from RBG Kew visited and wrote articles about the richness of the tree collection. Also around this time JC Williams brought Sargent from the Arnold Arboretum in Boston who declared that Tregrehan was the best thing of its type that he had seen, high praise indeed for a rapidly developing arboretum. 

The size and range of trees is stunning and the garden is rewarding to visit at any time of the year as so many of the trees are evergreen or coniferous. The collection has recently been reviewed by Owen Johnson from the British Tree Register who declared Tregrehan to be "The finest private garden in Britain and Ireland for its range and size of recently introduced tree species." He lists over 170 National Champions which puts it in the top half dozen collections in the country. He also lists a Picea sitchensis, (sitka spruce) growing on the valley floor at 153 feet which is the tallest tree presently on record in Cornwall.

The emphasis of much of the recent planting is on maintaining a "Safe Site" for trees that are endangered in the wild. Formal links have been established to access known source wild plant material such as the Conifer Conservation Group set up by RBG Edinburgh. The idea being that viable populations of endangered trees are established in ex situ collections as a back up to preserving these trees in their native habitats.   

Tregrehan was also chosen  to be represented in "New Trees. Recent Introductions to Cultivation" published in 2009 by Kew.  

The glasshouse range was built in 1845 on the northern wall of the remodelled walled garden. It was constructed with close-grained pine timber, using sliding sashes for ventilation and a twin boiler powered wet system for heating. The whole house is around 60 metres long and dominates the walled garden from all aspects.

It is one of the very few structures of this age and size that is still extant in the UK. Much work was done in the early 1990's to preserve the structure and replace much of the glass including the roof. Originally used as a heated show house for vines, orchids and camellias, it is now used to display shrubs, fruits and climbers that require some frost protection but no extra heat from the old boiler systems.

These were first planted in the woodland from the middle of the 19th Century when the range of plants available was hugely boosted by the exploration of areas in the Sino-Himalaya zones. There are still survivors from this period which have now reached a massive size. These first species mainly descended from original introductions from Sikkim by Joseph Hooker and were spread around many Cornish gardens. Rh. grande, arboreum, falconeri, hookeri and barbatum all survive from this planting time. 

These massive spring flowering survivors provide the main riot of colour in the spring and early summer. They provide a spectacle that is rare to see outside their native habitats in South East Asia, and only a few climatic zones in the world are suitable for generating such a display. 

This original 19th Century collection was added to in large measure by Rupert Carlyon in the 1930's and also by Tom Hudson over the last 25 years. Species make up the bulk of those planted and many are of a tender nature originating from the series Maddenia, Irrorata, Grandia, Falconera and Fortunea in particular. Most of these have been grown from wild seed in the nursery and often planted in small groups to aid conservation value and to make a bigger impact in the garden.  

The park consists of about 50 acres which wraps around the core part of the garden. It has evolved over the last few hundred years from a series of smaller mixed use enclosures into the open sheep grazed pasture of today. The large deciduous trees of English Oak and Sweet Chestnut dominate the mixed planting which also includes evergreen broadleaved trees and conifers.

Today sheep graze within a Higher Stewardship Scheme run by Natural England. This scheme requires a low fertility organic regime which helps to preserve the high biodiversity value of this old wood pasture system. Also within the HSS over 150 trees have been planted in the park to replace the rather elderly population many of which are 350 or more years old. 

Visitors are welcome to walk and take their dogs on leads into the park as long as the sheep aren't disturbed especially during lambing time. The views of St Austell Bay are spectacular and the Gribbin Daymark is clearly visible marking the entrance to Fowey Harbour. Special care must be taken as the ground is uneven and slippery in places and boots should be worn. 

The first camellias were planted outside along the various high walls of the Walled Garden. It was thought at the time that they needed the extra cold protection the walls afforded. They soon however outgrew the height of the wall and flourished proving that planting anywhere in the woodland gave perfect conditions. Quite a few of these original 1840's Camellia japonica plants still survive after being repeatedly cutback over the years and have developed tree like trunks at the base. They are some of the oldest Camellia plants grown outside in the UK, proving the  hardiness and the durability of the Genus.

Miss Gillian Carlyon loved camellias and started a hybridising programme in the 1960's using some of these old japonica camellias and crossing them with Camellia spp. saluenensis and cuspidata. She was at the forefront of camellia breeding at the time and was recognised by the RHS who presented her with the Cory Cup for the Camellia Jenefer Carlyon. About twenty or so were named and can be see throughout the top half of the garden.

Recently Tom Hudson has added to the camellia picture in the garden with a species collection. The camellia spp. are centred around southern China and North Vietnam at relatively low elevations. Notwithstanding this many are now flourishing outside and considering their origins, they are proving to be resistant to all but the toughest of winters; and there are now approximately 50 camellia spp. happily growing outside at Tregrehan. Many are scented, some have interesting coloured bark and all show different shaped and sized leaves which provide much year round interest in the natural conditions of the woodland.      

The large Asiatic tree magnolias dominate the colour show in the garden from early spring until the mass of other colour arrives later on in March. In a good year without cold frosts and damaging winds, they are the wonder of the large Cornish gardens and herald the end of winter and the start of warmer temperatures.  

These huge trees which flower before the leaves emerge in the spring are relicts from the beginnings of plant evolution. They vary in flower colour from white to a remarkable dark crimson red. The paler varieties especially can be seen in the woodland at a great distance even on murky days.    

Also in the garden at Tregrehan are another two groups of magnolias called Michelias and Manglietias. These are evergreen plants and vary in size from bushes to huge trees. They tend to flower later in the season; many have massed blooms and fill the woodland with scent. Rather tender in much of the UK, they thrive in the deep shelter of the garden at Tregrehan. Owen Johnson mentions 16 of these evergreen Magnoliaceae that are the largest of their type in the country showing how the garden is at the forefront of trialling these plants which have been recently been imported into the UK. 

There are several mature New Zealand plants in the garden that were planted in the 19th Century. Podocarpus totara, Podocarpus hallii, Griselinia littoralis and several Nothofagus spp. are all record sized specimens in the UK.  GRG Carlyon who was born in NZ and emigrated to Cornwall was a terrific plantsman and collector and imported many seeds from his homeland. He sourced much material for Tregrehan from his birthplace at Gwavas Station in Hawkes Bay. There the family has preserved 150 Ha of original lowland Podocarp forest which is a rare item with the wholesale clearance of this type of NZ bush country.

The original Gwavas homestead has been restored by Phyl and Stu Gibson to provide accommodation and entertainment facilities. The surrounding 10 Ha garden was started by ASG Carlyon in the 1880's and has been continually planted and is now maintained by Michael Hudson. It has been awarded a conservation plaque by the International Dendrology Society, one of only about 20 in the world, in recognition of the class of the plant collection.

Tom Hudson probably as a result of emigrating from NZ to Cornwall has also planted a collection of NZ plants. A separate area within the Gondwanaland part of the garden has been set aside for woody trees and shrubs from mid altitude NZ forest. The mixed broadleaf and coniferous tree mixture is virtually all evergreen so eventually there will be little light for the understory layer. Treeferns spore in the damp areas naturally and lianas and prickly rubus ramble right up into the crowns of the larger trees.   

The Araliaceae have become a major new component of the sheltered woodland garden.

Many new species are growing in the garden at Tregrehan for the first time in the UK. Genera include;

Brassaiopsis from Arunachal Pradesh in India

Dendropanax from Mexico

Gamblea from the Himalaya

Metapanax from China

Oreopanax from Mexico

Pentapanax from China

Pseudopanax from New Zealand

Schefflera from Vietnam

Sinopanax from Taiwan

Trevesia from Vietnam

Often reaching 10 metres or more in warm evergreen forest the Araliads are often confusing to identify as they continually change their leaf shape until fully mature and flowering.

With many trees and shrubs in this type of vegetation having a simple leaf structure they provide a welcome distraction with often bizarre leaflet shapes on the tips of huge petioles up to a metre or more in size. 

Plant collectors collectors such as William Lobb and Harold Comber introduced many trees and shrubs from South America which succeed in the mild Cornish climate. In fact several trees such as the Eucryphia cordifolia  reach a comparable size to that in their native habitat and spread around from shoots growing off their root systems. The South American Nothofagus spp. are all fast growing and successful trees for the woodland garden at Tregrehan. 

Tasmania and South Australia also provide much interest in the Gondwanaland Section at Tregrehan which is the area across the stream at the bottom of the valley. Different members of the Proteaceae such as Embothrium and Grevillea are prominent but rather fickle. 

Keep a look out for a series of different Bromeliads at the bases of the large trees where by being dry in the winter they survive the frost and cold. There are quite a number of interesting conifers here including Fitzroya and Pilgerodendron which were received from the RBG Edinburgh as part of their Conifer Conservation Programme.