Growing hardy orchids in the UK

“Growing Terrestrial Orchids in a British Garden”

The following advice on growing hardy orchids is an extract from the booklet....

Growing Terrestrial Hardy Orchids in a British Garden" by Jeff Hutchings. Price £5.00 plus £1.50 inland postage.

Where can you grow hardy orchids

Hardy orchids can be grown in most areas of a garden. There are those that like sunny borders, others rockeries or raised beds, some need the shade of shrubs or woodland, old unfertilized lawns or pastures make ideal naturalisation areas, some enhance the margins around ponds or other damp areas, others are more suited to troughs or pots and finally there are those that need the protection of cold frames or alpine houses for part of the year.

To grow hardy orchids successfully you need a basic understanding of your chosen species. All the hardy orchids grown outdoors in the United Kingdom are terrestrial and usually have a seasonal dormancy period within their annual growth cycle.

They can be divided into four broad groups according to their lifecycle and each of them has its own cultivation requirements.

1 Plants with a buried rhizome producing annual leafy shoots terminating in a flower spike, Cypripedium, Epipactis

2 Plants producing an annual root tuber (carrot or finger shaped) with a rosette of leaves in the spring flowering form a central stem in late spring and through the summer Dactylorhiza, Gymnadenia, Platanthera

3 Plants with an oval annual root tuber forming a leaf rosette in the autumn or winter and producing a flowering spike in spring or early summer followed by summer dormancy of some duration Orchis, Anacamptis, Ophrys, Serapias

4 Plants with pseudobulbs which spread across the surface usually developing new growth in the spring, either before or after flowering Calanthe and Bletilla

All the above can be classified as “Hardy” but because of the differences in winter climate in their natural habitat and the United Kingdom some need more specialist treatment in the winter than others. However, with the changes in our own climate cultivation suggestions written some years ago are no longer applicable. Because most peoples experience with orchids is related to the tropical species the immediate thought is winter protection against frost. This is often wrong as for many hardy orchids frost is a benefit rather than a problem. None of them need warmth in the winter. Keeping hardy orchids too warm often leads to bacterial infection.

What to grow?

Choosing which orchids to grow is not usually easy, although for those whose interest has been awoken by the sudden appearance of native species in their gardens, selection is a little easier. If your soil is the same as the surrounding countryside, why not try and find out which orchids grow in the locality as this will help you chose suitable subjects that are more likely to grow in that garden. Initially it is sensible to purchase easy species and then progress onto the more difficult subjects with experience. Alternatively, areas of the garden should be prepared in such a way as to provide the necessary micro climate for specific species.

Of the summer flowering species, Dactylorhiza, Epipactis and Platanthera are all good garden subjects. Most require a moist but free draining soil which is neutral or slightly alkaline. Most do not like drought so it may be necessary to water during the summer when they are still in leaf.

Cypripediums are becoming increasingly available and a small number of species plus many of the hybrids are relatively easy to grow in the appropriate situation. These are good for cool semi-shaded positions where they can be left to develop over a period of years. Alternatively, they make fine pot plants kept in the summer in the same conditions as those planted and put into a frame or cold greenhouse in the winter. Never into a heated area unless it is simply a frost free environment.

The winter green species, Anacamptis. Orchis, Ophrys with their specific requirements are not as easy. This is because many of them come from a Mediterranean climate where winters may be very cold but are likely to be reasonably dry. The best way is to grow them in pots and protect from winter rain. There are a number of native species available that grow happily in our climate provided the soil conditions are right.

Bletillas and Calanthe are good subjects for damp shady areas where there is some protection from frost. This can be assisted by covering with a layer of bark chippings in the winter.

Principles of cultivation

It is a simple matter to “kill with kindness.” Terrestrial orchid adaptations to enable them to withstand low nutrient regimes or periodic drought, are mandatory. Most have a defined dormancy period when they have no parts above the ground.

There were two distinct groups of growers; those who believed in ecological cultivation techniques designed to maintain and encourage mycorrhizal fungi at all times and the group who took minimum notice of the fungal relationship. Today, it is accepted that in the post flask stages mycorrhizal fungus are useful but not completely vital.

To cultivate a particular orchid you need the following information:

what are its requirements and how can you recreate them most easily.
is the plant fully hardy under our conditions?
would it benefit from winter protection against frost or wet?
does it come from an open or shady area?
are conditions predominantly dry or wet during the growing and dormant seasons?
is the substrate it grows in naturally acidic or alkaline, high or low in organic matter, well drained or moisture retentive?

Orchid Composts

The following ingredients are used to make up suitable composts for terrestrial species. Mixes can be used in troughs, pots and as replacement for existing soil; particularly in raised beds.

Loam – choose a loam which is well structured with fibrous material and a good mix of clay and sand. There is debate as to the need for the loam to be sterilised because of the effects on any fungus.

Sand/grit – 4-7 mm sharp sand or grit which will help keep the mix open.

Leafmould – the best leafmould for orchids is beech or alternatively if available use pine duff from the floor of a pine forest.

Peat- sphagnum moss/peat is the best for use with orchids.

Bark- use fine or composted bark, preferably pine.

Seramis – is a proprietary product form Germany. It is consists of porous clay modules which both aid drainage and hold sufficient water to avoid plants drying out.

Perlite – is another form of inorganic product which operates in the same way as Seramis.

Mix for dactylorhiza and other large tubers

2 parts loam + 2 parts peat, + 1 part sand/grit

Mix for cypripediums

1 part loam + 3 parts sand/grit + 1 part mix of leafmould/ composted bark or peat

and 1 part Seramis

Mix for Anacamptis, Orchis and Ophrys

2 parts loam +`2 parts sand/grit + 1 part leafmould/peat +`1 part Seramis

Mix for other woodland lovers

2 parts loam +1 part sand + 2 parts leafmould/composted bark

Adjust for pH by adding dolomitic limestone or use appropriate loam

Tips for planting

Dactylorhiza tubers must never be allowed to dry out. This is especially important with those grown in pots. Primarily whilst they like damp they do not like standing water. They do like humus rich soil but with good aeration. Having said that some species thrive in the wet areas and margins around ponds or in bogs I have seen plants growing very happily in large pots of a very sandy compost. They are happy in full sun or part shade depending on the species. In summary they are idea for borders or naturalising in an old grass area or in decent sized pots.

The favourite time for planting is either autumn or spring prior to dormancy break. Try to plant with any existing soil. Make sure the soil is dug over to a depth of 30 cm and plant with the tuber fingers fully spread and the crown about 3cm below the soil level. For those species liking alkaline soil dig in a quantity of dolomitic limestone.

Calanthe require shady conditions with a slightly moist humus rich soil and should be planted just under the surface. A top dressing of leaf mulch not only aids growth but also winter protection.

Cypripediums can be grown either in large pots (to allow the rhizome to spread) or in sheltered semi-shade in the garden. In both situations certain cultivation techniques are a must. The plant must not be allowed to dry out during the summer and conversely must not be allowed to become waterlogged during the winter. My recommendations for planting in the garden are that the existing soil be removed and a purpose made compost used in order to ensure that the plant is adequately drained and the surrounding area the correct pH. Unlike most of the other terrestrial orchids cypripediums should be fed throughout the growing period with a weak solution of something like Tomorite every fortnight from when the initial growth is about 5 cm tall until late September.

To protect against winter rain plants in the garden can be covered by an inch of grit and then place something like a ridge tile on top. For plants in pots they should be kept fairly dry during the winter with any watering being done around the edge of the pot and not over the dormant buds. I do not water the whole plant until growth is established in spring. A critical point is timing of winter watering. Never water the plants if there is any likely hood of frost unless you cover the pot with fleece or bubble plastic during that period. This is to avoid any chance of damp roots becoming frosted and ultimately killing part of the plant. The most sensible idea is to put pots into a cold greenhouse, cold frame or even a garage from November to late February.

Winter green species grown in the garden should be protected in the winter by covering with clear cloches, whilst those in alpine houses or cold frames should be plunged in sand and watering is by keeping the sand damp. In times of frost the plants could be fleeced over. In this way the tubers and roots are not damaged by the frost. A further problem with these species in the spring is one of our usual problems, namely slugs, snails and in my nursery either mice or wrens. Planting into a meadow involves removing an area of the turf and fully aerating the soil below. The tuber should then be placed into the soil and the turf replaced. Mark the planting site so that plants can be regularly checked. Any planted grassland area must not be mown until at least July in order to allow the orchid to complete its full annual cycle.