Specific Families and Genera > Saxifraga
Saxifraga 2018
David Sellars:
Temperatures in this part of the world have been above freezing for all of January and although there has been endless rain and very little sun the Saxes are starting to flower. Saxifraga Franz Liszt is growing in a vertical tufa crevice under a rock overhang. This keeps the flowers dry.
Saxifraga Frederik Chopin and Saxifraga Radvan Horny are growing in a plunge bed in the Alpine Shed.
Jan Tholhuijsen:
Nice pictures David, I start with just a few flower buds in the open greenhouse.
kris:
very nice plants, Jan and David. I can't grow them like you. Either weather or my mistake they don't look as healthy as yours.
David Sellars:
Kabschia Saxifrages should do well in Saskatoon, Kris. They are very cold hardy but cannot tolerate heat. Kabschias must be kept cool and moist in the summer and I have found that the best location for potted Saxifrages is on the north side of the house in complete shade most of the day but open to the sky. Shade cloth can be unsatisfactory because it traps the heat.
The best potting mix for Saxifrages has been debated over the years. Many in the UK use a mix with John Innes compost which is not available in Canada. A few years ago I visited Phil Pearson who ran a Saxifrage nursery near Seattle with Steve Doonan. The mix they originally developed had very little peat in the mix and Phil has since moved on to just using pumice.
A potting mix only with pumice is too loose for my taste as it all falls apart when a plant is repotted, plus you need a lot of pumice! I now use a mix that is about 50% coarse sand (that also contains rock dust), 25% pumice and 25% limestone chips. This mix is very free-draining but still clumps together when moist. Saxifrages love this mix and quickly grow long, healthy, well-aerated roots to the bottom of the pot. The absence of any organic matter does not seem to be a problem and in fact I believe is an advantage as it is impossible to over-water. I suspect that Saxifrage pots with soil or peat in the mix can easily get too warm in the summer. The gritty mix with no peat can be kept well-watered to keep the roots cool.
The rock dust provides mineral nutrients and very little additional fertilizing is necessary. For the potted Saxifrages I follow the fertilizing practice of Wisley Gardens with dilute high potash fertilizer just twice a year, in the fall and after flowering. It is quite possible that the pumice and limestone chips could be replaced with granite grit. But now that I am happy with my mix I have no incentive to try something different!
The following photos show how well this potting mix works. I made a cutting of Saxifraga Květy Coventry in September 2016 and potted it on in February 2017. At that time the cutting had formed only tiny roots. A year later (February 2018) growth has been vigorous and the roots are emerging from the bottom of a 90 mm deep pot. The white roots are recent root growth.
Leucogenes:
Thank you very much for the fantastic explanations... David. I have a few saxifraga, but all outdoor in combination with various sempervivum. I'll get some more copies, though. Your comments on the substrate are therefore very helpful.
Thomas
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