This contribution deals only with the cultivation of Himalayan androsaces in pots.
All seed is sown on a single compost, i.e.., 60% very sharp 2-4mm grit, 30% fine grade Cambark & 10% John Innes 3, surfaced with a gently firmed 1mm layer of sieved peat. Sown seed is covered only with a 5mm layer of grade 2 Flintag (100% silicaceous grit, nominal size 2-3mm); pots are then soaked from below, gently watered from above using a fine rose and placed outside, fully exposed to the elements. Seed, regardless of the date of receipt, is sown around the New Year, or as soon as received if after this time.
In my experience, seed of most Himalayan androsaces does not have any particular requirements to trigger germination other than a general rise in temperature such as is generally experienced in southern England in late February & early March. Seed received from the Kunming-Goteborg expedition (KGB) in late February 1994 & sown immediately started to germinate in late March 1994, whereas AGS China expedition (ACE) seed sown at Christmas 1994 started to germinate in mid-February 1995 with germination continuing into early April. Interestingly, seed of Androsace bulleyana was the last to germinate from both collections. One exception to this general observation is seed of two collections of Androsace delavayi made by the KGB expedition; no germination was experienced in the first season following sowing but several seedlings germinated the following spring.
Treatment of Seedlings
As soon as any germination is apparent the pots are brought under cover. When the cotyledons are fully developed, and there is an indication of formation of the first true leaves, the seedlings are pricked out into 2.5" pots using a compost consisting of 70% sharp grit, 15% John Innes 3 & 15% sieved ericaceous compost. Seedlings are kept shaded for a week then in the greenhouse for a further 3-4 weeks before being grown on in an Access frame with some protection from heavy rain until well established, & shading at all times from the hottest sun. Copious amounts of water are given.
Mature Seedlings and Established Plants
All of the above are grown in Access frames, no Himalayan species are kept in the alpine house at any stage other than as immature seedlings. Roof glass is kept in the frames from early October until after flowering (mid-April), side glass is only used in the winter during prolonged heavy rain or when temperatures fall below -3 o C. Watering in the pots commences after Christmas and is increased throughout the early spring until, following flowering, water provided by rainfall is supplemented where necessary with overhead watering using a fine rose on a hose-pipe. Androsace muscoidea var. longiscapa seems particularly susceptible to crown rot in late summer, this may be a reflection of the drier conditions experienced by this species at this time in it's native habitat. Consequently, overhead protection is provided from early August. Androsace spinulifera (KGB seedlings) was lost completely to crown rot following the onset of dormancy in late September even though no water had been given in the pots for several weeks. This species has a reputation for difficulty in this respect & ACE seedlings have been moved into an extremely gritty compost with pure grit from the point of emergence of the roots to the crown of the plant.
In a normal summer very little shading is provided, plants are grown with full exposure to the sun from mid-morning until late afternoon. For example, during the relatively hot summer of 1994, shading in the form of a single layer of 30% shade netting was provided only for 5 weeks during mid-July to late August. Androsace rigida , rigida var. minor & spinulifera (KGB seedlings) were particularly affected, the foliage becoming lime-green, although I suspect that the major cause of the plants distress was prolonged temperatures over 75 o C rather than excessively high light levels. Healthy growth resumed as soon as the temperatures dropped. Saxifraga georgii & S. lowndesii and Solmslaubachia spp. are ideal indicator plants for heat stress, the foliage being among the first to show the adverse effects of high temperatures.
As soon as good root growth is seen to emerge from the bottom of 2.5" pots they are moved into 3.5" clay pots in the same compost as above; all clay pots are plunged in sand. Henceforth, they are potted on every year, no nutrient is given other than that contained in the compost. Root aphids, green fly & red spider mite are the major pests with which I have experienced problems but damage can largely be avoided by suitable prophylactic treatments. Root aphid is prevented by drenching the compost in early spring and late summer with spray-strength dimethoate (commercially available as Murphy's Bio Long-Last in combination with permethrin), green fly and red spider mite are fully controlled by over-head spraying with dimethoate or bifenthrin (available as Polysect) at regular intervals. Species which, in my experience, are particularly susceptible to red spider mite include Androsace tapete & A. villosa var. arachnoidea.
The major fungal disease is botrytis, which is mainly a problem on senescent foliage. Very effective control can be achieved by overhead spraying monthly from September to late December with Rovral (Iprodione), a specific antifungal agent. This is, however, no substitute for regular observation and the rapid removal of any diseased growth. It is interesting to note that botrytis on any plant is always far worse in the alpine house than in a well-ventilated outside frame. I would go so far as to suggest that the alpine house is totally unsuitable as a home for any Himalayan androsace (or saxifrage) other than small seedlings.
Propagation is an absolute requirement for the successful maintenance and distribution of any species. Germination of wild-collected seed (or home-saved seed in a few cases) is usually very good & should result in a high percentage of flowering-sized plants. Androsace rigida , for example, flowered well the first spring after germination. Unless large populations of mature fertile plants can be maintained it is likely that future propagation will rely on vegetative means. Every effort must, however, be made to cross-pollinate different plants as this is the sole means to ensure the survival of healthy, genetically diverse, individuals of a given species. Vegetative propagation is via the rooting of single rosette cuttings; this is relatively straightforward as long as cuttings are taken at the correct stage of growth. A common mistake is to take cuttings too late in the season when the runners have started to become woody - young, soft daughter rosettes with 0.5" stems will give better than 90% success if taken into silver sand in a propagator. The optimum time to take cuttings varies greatly; Androsace mucronifolia is generally propagated in early April, immediately after flowering, at a time when Androsace muscoidea var. longiscapa , for example , is still dormant. Rooting will usually occur within 4 weeks and plants can be potted up immediately to make strong plants which will over-winter without difficulty.
The cultivation of androsaces in the south-east of England should, with sensible attention to their basic requirements and regular propagation, be no more of a problem than anywhere else in the country. There is absolutely no substitute for continuous observation of your plants - they alone will tell you whether they are happy - although it is up to you to decide what they are saying !