Saxifrages from seed
by Malcolm McGregor
Growing saxifrages from seed is easier than I had ever thought it would be - I had always thought it would be almost impossible: the plants were so slow that the seed would be impossible to germinate; the seedlings, if any did appear, tiny and irremediably perverse. Kabschia saxifrages never self-seeded, any more than the silver saxifrages seemed to, so it would not be realistic expect any success. Which is why, I suppose, it took me so long to try it - that and the fact that my father, who's usually pretty good with seeds, had not got anywhere a few years ago with a packet of Thompson & Morgan's "One Hundred Saxifrages Mix'. Anyway, it turned out, when I did finally try, after about ten years of growing Kabschias, to be relatively straightforward.
What sparked me off was the desire to maintain Saxifraga media in my collection when my plant only had one rosette but was about to flower. Perhaps it would set a side rosette or two before it died but perhaps not.
Growing from Seed
My approach to growing alpines from seed stems from a lecture by Mike Ireland to our local AGS group in Beverley. The fundamental approach is to use a richer mixture in the lower part of the pot and a seed compost mix in the upper part. This is to allow the seedlings to remain in the original pot for a whole year if necessary before potting on or planting out. I always use plastic pots and they generally have an internal rim about half an inch down so that tends to be the indicator used. Up to this line (roughly) fill the pot with a mix of equal parts JI2 and grit. Top up to the rim with a mix of equal parts JISeed and grit. I then smooth off any excess with a straight edge. Then tap the pot to settle the compost and I then firm it down by pressing it with the base of another pot. This will usually take the level nearly back down to the ridge again.
The seeds are then sown on this firm bed. If the seeds are large (saxifrage seed is not) then I might sprinkle them with a little extra of the seed compost mix although I do not usually do this. Just occasionally with very large seeds such as Paeonia seeds I press the seeds into the compost. This is then topped off to the top with grit. I vary this to some extent with saxifrage seed in that I sprinkle some grit on the surface of the compost before I sprinkle the seed and then top off with a little more grit. I have tried adding all the grit before sprinkling the seed but now prefer a halfway house of grit-seed-grit. Having done this (and labelled each pot as I do it) I soak the pots by standing them in a tray of water until the surface of the grit shows that it is damp. I keep notes of dates that I sow seed and the date of first germination. If it is seed I have had a hand in collecting or hybridising I also keep notes relating to those dates.
The pots are kept then in trays either in a cold frame or open to the elements but not directly exposed to the sun. Once seeds start to germinate it is important that it does not dry out. Since it is not obvious when germination is going to start it is best to ensure that the whole thing never dries out completely. All seed is treated in the same manner until it germinates: none is chilled in a refrigerator; none is heated in a propagator; it is left as exposed to the elements as is consistent with it not drying out or getting baked. A sample of seed of S. oppositifolia 'Theoden' germinated rapidly after chilling for three weeks in a refrigerator but then it germinates successfully without this treatment.
The important characteristics of this method, for which I wholeheartedly thank Mike Ireland, are that the seedlings have half an inch or more of seed mix to germinate on or in and then grow in before they, as slightly larger seedlings, reach the richer mix below. This allows the seedlings to be left for longer in the original pot before they exhaust the mix. It does seem important to use at least half grit in the mixes, and with some bags of John Innes which seem deficient in this respect I may well add quite a bit more. I have tried adding Cornish Grit instead of more normal quartz chippings but I find that makes the mixture drain too well although it should be stressed that the East Coast of England is a low rainfall area. In mid-Wales my father finds this a valuable substitute for at least part of the mix.
Saxifrages are dicotyledons which means that when the seed germinates it produces two seed leaves (cotyledons). In the case of saxifrages these can be very small indeed and searching pots for first signs of germination is something that is aided quite a lot by a hand lens. Quite soon the first proper leaves start to form as a pair between the pair of cotyledons. All Porphyrion and Ligulatae saxifrage seedlings develop their first proper leaves as a pair only later gradually adopting the adult leaf formation if that is not of opposite leaves. These first proper leaves can often be seen to have lime glands.
Germination can be quite a slow business with seedlings having been reported as appearing after four years or more. With old dried seed this can be true but with fresh seed germination often occurs within a few weeks. In some cases germination is after about fourteen days so it pays to start looking almost immediately. Generally if the seed has not germinated after two winters I give up on it. Moss, liverworts and weeds generally have overtaken the pot in that time and the space in the frame has new demands on it.
Until this year I have left seedlings in the original pot until they are well on their way, usually some months, before moving them on. This has advantages: the most vigorous seedlings are recognisably saxifrages, their rosettes well advanced; there is less urgency about the process; the seedlings are robust enough to transfer easily and few succumb to the move; the best looking seedlings can be selected. However prompted by Sergio Bacci's technique of moving seedlings on almost as they germinate I have experimented with this approach this year, moving a small number of seedlings on whilst they had only seed leaves. These are then kept in a plunge bed whilst leaving the others behind in the original pot. It is quite clear that some of each batch of the transplanted seedlings have made much more rapid progress than the ones left behind, although others in the batches show no acceleration in growth. The disadvantage of the method is the need for fine tweezers, a lens, and a steady hand.
This is not a common Engleria species in cultivation so when I got one from Holden Clough nursery in 1987 I was very interested in what would come of it. It took a year and a half to come to flower but it was very satisfactory. The dark red one-sided inflorescence was very much in line with the illustration in Porophyllum Saxifrages so I decided to try and keep it going from seed. Perhaps it was intuition as the plant did not flower again before expiring the following year, without ever having produced a side rosette large enough to take as a cutting. Before insects got to the flowers I fertilised them using a small brush and then kept the plant covered until the seed had set (something I continue to do when I want to make sure that it is me that is determining the outcome rather than some wandering insect - a bell jar or a sawn-off plastic lemonade bottle are both effective). This tends to take about two weeks. After fertilisation has taken place and seed has set there is no further need to protect. It took about another month for the seed to ripen. It is quite easy to tell when it is ripe since the twin-chambered capsule first swells then splits to expose the seed within.
The seed set was good and unlike much saxifrage seed it turned out to be seed of a decent size; not that I realised almost all later seed would be smaller: some like S.chrysantha is tiny. I sowed some of the seed immediately, both in a separate pot and in the pot with the parent plant. Germination was delayed until spring 1990 but I managed to get quite good germination. The seedlings were slow but I now have ten growing on successfully in a limestone filled trough and have passed quite a few on to friends. I have hopes for some flowers in 1994. As all of the seedlings, like the parent, have failed to have any side rosettes I shall probably have to repeat the process. Although not a monocarpic species, which dies as soon as it has flowered, this particular strain is obviously nearly so.
The seed was collected in the Spanish Pyrenees by my younger son and me in early August 1990. Growing plants, which had not flowered, could be found with their rosettes up to 12" (30cm) in diameter which is very much at the upper end of the size mentioned in texts. Since flowering was over for the year these had at least one more year's growth left in them before they would flower.
The collected seed was split three ways on return: John Howes in Hull, and my father in Dyfed both sowed theirs immediately and the first germination for each of them was after about two weeks. My sowing was delayed about a month but again germination was within a fortnight. The seedlings were numerous and vigorous and each of us had no great difficulty keeping them going under our differing regimes. Kept in pots I have still got a number which are no more than an inch in diameter with one up to about 21/2" (6cm).
Three were planted out in 1992 in a large shallow sink filled with half and half JI2 and limestone chippings with some large limestone pieces. Planted with their roots under the southern face of one of these the three are now 4", 41/2" and 51/2" in diameter. [Those measurements were in early March 93, on lst September they measure 9", 10" and 111/2" respectively.]
Saxifraga poluniniana as a parent
Having tried growing a variety of saxifrage seed from a variety of sources I decided to try hybridising in late 1990 and in late March 1991 I pollinated flowers on two flower stems of S. poluniniana with pollen from S. 'Winifred' having first removed stamens and petals from the flowers I was pollinating. The plant was kept covered to ensure no accidental pollination until seed had set.
I collected the seed in May as soon as the capsules started to open and sowed it immediately. First germination was in exactly 14 days. With almost no exceptions the seedlings were vigorous and in the early autumn I was able to transfer between 60 and 70 seedlings to a 10" pan filled with 50:50 JI2 and grit. This was kept overwinter in a plunge bench in an alpine house and 5 seedlings flowered in Feb/March 1992. Three of these were very similar with flowers opening with budbreak being lipstick pink and the flowers paler. One of the others was far paler and the fifth was darker than the majority, a somewhat musty crushed strawberry colour. All the transferred seedlings have survived so far, some now being about 11/2" in diameter. [on lst September now 4' across]
It is quite clear that S. poluniniana x S. 'Winifred' is a fecund cross producing vigorous and highly variable seedlings. At the moment the rush seems to be on to name seedlings as fast as possible. Little opportunity has arisen for any evaluation of some plants that are being named. Among the binomials published in Porophyllum Saxifrages very few binomials had even 20 named and distinct members. This new cross already has about nine, and so far the only S. x anglica cultivar to be used has been 'Winifred'. [Having written that particular comment in January I have since tried S.'Christine' as the pollen parent - seedlings are progressing well]
One of the significant things about different individuals of a species, plant or animal, is that they are all unique. No two individuals are identical: it is a fact which is easily forgotten and it is what drives evolution.
In fact it is not quite true or sufficient to say that every individual is unique. Identical twins are very similar to look at, sometimes remarkably so, but it is not their looks which make them identical but their genetic makeup: their appearance is only an expression of their identical nature. Accidents of upbringing or environment may make them physically different: a plant or animal may be lucky with nutrients, warmth and shelter, or unlucky and be stunted or damaged. And as accidents, lucky or unlucky, can affect an individual so too can deliberate actions. With children it can be to broaden intellectual horizons and opportunities; with plants it can create bonsai trees from forest giants, or the symmetrical over-perfection of the showbench medal winner. But underlying these differences, deliberate or accidental, are the genetic similarities and dissimilarities. It is this variety which provides the evolutionary potential, but for the plant breeder only some variations are of value: larger petals, better constitution, more fruit, different colours, more flowers and so on.
The approach to the propagation of plant species and hybrids differs therefore fundamentally. With species there is a genetic diversity existing in wild populations which can only be represented and encountered through the use of 'true' seed. In the garden this means that there is the need for some sort of precaution to avoid accidental cross-pollination with plants of another species, or with hybrids. In extreme cases it may even be important to keep separate stock from different geographic populations of the same species to maintain this genetic separation. Vegetative propagation will ensure that no outside influences come in but also stop any of the natural variation occurring. Cuttings therefore eliminate variability, and whilst maintaining particular clones in their pure state, can lead to problems if viral disease weakens the stock.
With hybrids the situation is totally different. Whereas all plants of S. longifoliai are genetically different; they have to be grown from seed since the species is monocarpic; all plants of a hybrid cultivar such as S. 'Tumbling Waters' or S. 'Winifred' are genetically the same; they must be propagated vegetatively through cuttings or division. If a hybrid cultivar is propagated by seed its genetic purity, which is what keeps every plant the same, is lost. So 'true' plants of 'Winifred' have to be propagated by cuttings and 'true' plants of S.aretioides, for example, may be obtained by cuttings or from seed. It also means that any plant you grow from seed may be significantly different from previous plants: the newer the cross the more likely you are to get something different. What should not be overlooked however is that seed from crosses is not always viable and may be weakly or very difficult to grow. In some cases of course it may be impossible to carry out the cross successfully. With species the situation is often very straightforward. The seedlings may be quite vigorous. If the plant is monocarpic indeed the only way in which the plant reproduces is from seed, so although it may not be easy to germinate, it must be possible.
The three plants I have written about in some detail are some of my successes, obviously, but they represent three situations. Saxifraga longifolia is monocarpic and wild collected seed is one of the few ways in which the true plant can be grown. Hopefully however I can adopt a similar strategy to that which was successful with Saxifraga media where I was concerned to keep a species I had in cultivation and to make sure that I kept it genetically pure: isolate the plant prior to flowering, self-pollination and covering until seed is set.
In the case of crossing S.'Winifred' with S.poluniniana I was quite deliberately crossing two plants which I knew from other people's successes were likely to produce good results. It may seem odd to repeat someone else's cross but it is nice to experiment with something that is likely to work. Plenty of other attempts at crossing have produced no seed, non-viable seed, or no germination for other unknown reasons; but I now have successfully produced other crosses including S.stolitzkae x S.Winifred' a very attractive cross now designated as Saxifraga x baccii.
Growing saxifrages from seed has given me enormous pleasure. It is a lot easier than I had expected and yet not so easy as to lessen the thrill of finding the first seedling in the pot. Seeing it come to flower is genuinely satisfying. Seeing the first flower on a new hybrid seedling of your own is thrilling: it may not turn out to be beautiful or to be an improvement but for one moment you are God.