Prior to our 1995 move to the USA, daphnes formed a relatively peripheral part of my alpine plant 'portfolio', being represented by the staple pot-grown diet of Daphne petraea, D. petraea Grandiflora, D. arbuscula and D. jasminea . Our English garden was really too small, and the aspect unsuitable, for many of the larger species. My main interest was in the cultivation and propagation of alpine Primulaceae, saxifrages and various other cushion-forming species. The hardy bulbs which are a major part of my life now were also relatively poorly represented, and, again, were strictly pot grown.
The rapidity of our move to the USA (13 weeks from blissful ignorance to moving into our Exton house) meant that my entire plant collection had to be given away and new homes found for my alpine houses and cold frames. In some ways this 'clean break' preserved my sanity, and I had thoughts of endless hours golfing. Kath Dryden shattered that illusion within a couple of weeks, sending me the first of many parcels of treasures, and a hoop-house was up by Thanksgiving Day. We had swapped our 30' x 90' garden in England for 1.5 acres of untamed PA, about 1 acre being deciduous woodland on a slope above the house, the remainder being fairly open. There was obviously tremendous potential for a wide variety of plants and in that first year my major success was with the crab grass that covered the yard (garden) at an alarming rate. Crab grass is very un-English, and no-one explained the finer points of prevention until it was too late! Four years later we finally have a respectable lawn.
We are in US hardiness zone 6b, although much of our property is south facing and on the south side of a ridge, so protection from prevailing winds is very welcome and we are often a few degrees warmer than the valley floor. Frosts are also rare, the humidity being so low during the winter months. Our minimum temperature, to date, has been –4F, the maximum over 100F. July and August are hot (1999 gave us 28 days over 90F in July) and very humid, one of the main reasons why I haven't tried to rekindle some of my previous alpine plant interests. Summer storms can be frequent and severe but summers can also be very dry. Summer 1999 was the driest in living memory and was broken courtesy of Hurricane Floyd's 11" of rain in 16 hours. Summer heat is a major factor facilitating the growth, winter survival and floriferousness of trees and shrubs but the second important factor is the length of the growing season. The latter generally runs from April into November and has much to do with the success and spectacular performance of magnolias and daphnes, in particular.
Winters are much colder than we experienced in the south east of England, snow cover has been as low as 2" and as high as 64" but is very unpredictable. Freezes can extend for many weeks. The single most satisfying climatic difference between our US and English gardens is in the difference in the number of days on which the sun shines. In an average week I would estimate we get 5 sunny or partially sunny days, and this makes a major difference to the quality of the plants and the blooms.
After years of persuading small plants to grow in equally small pots, largely for the purpose of showing at AGS shows, I determined to grow as much as possible in the garden with the minimum of protection. However, in the early days I had no idea about the climate or growing conditions (which have turned out to be very well suited indeed to growing many plants), so I started off with the hoop-house, a greenhouse and a couple of cold frames. Over the last 3 years the majority of plants have graduated to a number of raised beds, sand beds and woodland areas that have been cleared and planted up. The only plants which remain in pots for any length of time are bulb seedlings, a number of the more tender Cyclamen species which will definitely not grow outdoors and potted, rooted daphne cuttings.
So, after much preamble, to the daphnes, which are much underutilized and under-appreciated in the USA. They are also largely unavailable, especially the dwarfer species and hybrids. Kath Dryden has had a major influence on my entire alpine 'career' and that has never been more appreciated than since our move. Many of my daphnes have come from Kath, others who have been very generous include Rick Lupp, a very skilled nurseryman with a wonderful range of true alpine plants and shrubs, and John Bieber. Cuttings and small rooted plants will happily make the journey across the Atlantic, with proper packaging, and either root or grow-on very nicely in their new home.
Many of my smaller species and hybrids are planted in a raised bed bordering the driveway (basketball practice around the nearby hoop provides an occasional source of cuttings). Exposure is very open, although an old willow does give a little relief. The bed is raised about 6" and contains a mixture of regular topsoil, fine granite grit and peat, although some areas are very sandy to improve the drainage for a number of crocus species. The entire garden is very rocky and sandy, so drainage generally is superb. daphnes in this bed include Dd. petraea, petraea Grandiflora, jasminea, x hendersonii x thauma, Leila Haines ( cneorum x striata ), Lawrence Crocker, Kilmeston ( petraea x jasminea ), arbuscula ssp. radicans and several clones of arbuscula. No protection from the elements is provided and the plants have been in there for 3 years. This winter the low was 3F (no snow) and at times the bed was covered with over 24" of snow. I have absolutely no doubt that, under my conditions, both D. jasminea and Kilmeston are hardy, they appeared from under the snow in exactly the same condition they were in last fall and are growing away again now. This past winter was the coldest experienced since 1995 and caused almost total defoliation of Leila Haines – however, the plant, now some 8-10" across and almost prostrate, is covered in swelling buds. The only casualty in this bed has been a large plant of D. x hendersonii which died rapidly from root rot at the end of last summer, during which the plants were repeatedly stressed by heat and drought. None of the plants here have been pruned and all are very compact.
Across from this bed is a steep sandy bank, directly exposed to the sun all day, and on which grows my 4 clones of D. genkwa (large-flowered form, an unnamed clone from John Bieber, the Hackenberry form and another unnamed clone). The Hackenberry form does vary from seed but generally has small pale flowers. Plants have grown very rapidly and vary significantly in their habit, all require regular pruning to look of their best. One disturbing feature is their propensity to split at the branch points, although they seem to rapidly heal and rarely lose branches this way. Plants are just coming into flower now and have never, to date, been damaged by late-season cold. D. genkwa also grows in front of the house, another hot and sheltered location over a very sandy sub-soil, along with 2 cneorum clones, D. oleioides ssp. kurdica , D. x napolitana and a very small plant of D. circassica. Just recently planted in the same bed are 2 plants each of D. bholua and D. odora aureomarginata. I think these may be hardy but time will be the judge. The cneorum clones tend to have large numbers of what look like fasciated flower buds, which then go on to open normally. I'd be interested to hear if others have seen this phenomenon. D. oleioides remains the only daphne I have completely failed to propagate by cuttings, but more of that shortly.
The back of the house gets some shade in the morning and late afternoon but gets the full force of the noon sun. I have built raised beds here also, varying from 15" to 24" in height and the soil is significantly richer. I have taken a decision to amend the native soil as little as possible, in most cases not at all, but the beds here were filled with a mixture of top soil and mushroom compost when we first moved in. D. retusa, arbuscula, collina, cneorum pygmaea alba and Rosy Wave all grow happily here although the Rosy Wave, at around 24" high and around, looks a little incongruous as a backdrop to the totally prostrate 8" mat of the white cneorum pygmaea. Further along, planted directly into the native rocky sand at the edge of the woodland, are D. x mantensiana, and D. caucasica . Both are thriving but reasonably careful watch has to be given to watering as these can wilt in extreme drought. Generally, in the absence of rain, the woodland beds are soaked overnight about every 10 days. Daphne x mantensiana and D. caucasica seem to be the most prone to winter damage, generally in the form of burnt leaves. However, none have defoliated to date and flower buds come through unscathed.
John Bieber has recently and very kindly given me a number of daphnes, including a number of D. x burkwoodii clones and other larger species. It is too early to say how these will do, but they have all been planted in the sunny, edge-of-woodland conditions that D. caucasica appreciates. A 2 year-old plant of Daphne x burkwoodii Carol Mackie is doing just fine in this situation. None of my plants receive any additional fertilizer, and pests and diseases have been minimal so far. However, the root rot which took my D. x hendersonii was likely due to Pythium or Phytophthora fungal species and I may consider occasional drenches with a suitable fungicide on plants which are particularly prone to it. This treatment is certainly used to control the problem in pot-grown plants in the UK.
As alluded to above, all of my daphnes are propagated yearly, from cuttings, using the same technique for all. I have not attempted grafting yet, largely because there has been no need and plants on their own roots grow very satisfactorily. Cuttings are taken in mid to late June, depending upon the season and the state of the new growth, and are of a size appropriate to the plant. Lower leaves are stripped away, and, in the case of the large leaved species, are cut back by half. They are then dipped in a diluted hormone rooting solution and struck into prepared flats. I routinely use regular seed flats, each can accommodate around 80 cuttings. The flats, 2.5" deep, are filled with nothing other than dry children's play sand – fine pure silica which does not bind and provides excellent contact with the cuttings and excellent drainage. After insertion, the cuttings are watered overhead, allowed to air dry, and the flats covered with a plastic dome with adequate head-height. The edge of the dome is offset slightly to allow some ventilation and the flats put in an open position which receives no direct sun. Any cuttings which rot usually do so quickly, and these are removed. Other than that, and maybe 2 waterings at monthly intervals or so, the cuttings get no attention until October, at which point all are carefully lifted and potted up. At this stage I get around 85% take of the cuttings I took – with the exception of Daphne oleioides ssp. kurdica, which rots without fail, regardless of the timing of the cuttings. Certain species and hybrids root more easily than others but none have been problematic. D. genkwa needs to be allowed to harden off a little – green cuttings fade away very quickly.
Rooted cuttings are potted up individually into 3.5" pots. I originally used a 50:50 mix of a peat based compost and granite grit, which worked quite well but has a tendency to be very heavy and also to stay wet for a while after watering. As of last year I went over to a compost (BioComp BC5) made largely from composted peanut hulls and this has proved very successful with the daphnes and a whole host of unrelated bulbs and woodland plants. Drainage is superb, it holds moisture well but is never soaking wet, other than just after watering. It is acid, around pH 5.5, but then so is much of our garden, and the daphnes have never complained. If plants are to stay in it for any length of time, supplementary feeding is recommended, including minerals and micronutrients, but I haven't done this to date. As an added bonus, the compost is inoculated with a fungus which is supposed to give protection against Pythium and Phytophthora pathogens. After top-dressing with granite grit, the pots are watered and over-wintered in a freeze-free greenhouse, kept just moist. Of the 250 cuttings potted up last fall, I have lost around 10, as of this week, and most are growing away nicely. I was very surprised to see some D. genkwa cuttings growing away, even though they put on no new growth before losing their leaves for the winter.
That, basically, is the story so far. Results have been excellent and the hope is that they will continue that way. As with any form of gardening, especially alpine, the key to success is to work out what the plants need in your situation (not necessarily what they are supposed to need) and to try them in a variety of sites and microclimates. The vital element to allow you to do this is propagation – not only does this give you the material to work with, it also provides extra plants which hopefully will transfer the highly virulent and lifelong desire to grow them to the unsuspecting recipients.