North Wales Diary Discussion: Cassiopes and peat
Started by: John RichardsGo to latest contribution by John Good, 29 May 2013, 18:48. Go to bottom of this page.
Loved your recent entry, and amazed at the quality of your rhodos. Lots of other favourites,not least the Paeonia ostii. I was interested in your non-PC comment about cassiopes and peat. When I first moved to Hexham in the early '70's there was no fuss about peat and I used to make whole beds of nothing else. I grew the most super cassiopes. These days I really struggle with them, they die-back and look miserable, grown in more of less pure leaf-mould, but I have not used peat for many years. I have a theory that like some other Ericaceae, cassiopes abhor nitrate. Whereas leaf-mould should have relatively little nitrate, there has been such an increase in NOX salt deposition from rainfall due to car exhausts that I bet it is now much more N-rich than pure peat, particularly sphagnum peat which can probably chelate anions as well as cations? Is this an argument for a renewed popularity of peat as a medium for growing N-sensitive plants?
Hi John, Thanks for your kind comments, and for opening up the can of worms regarding use of peat that I carefully put before my readers! If my memory serves me right (!), it has been shown experimentally on several occasions (I would need time to find the sources, but the late Dr Henry Tod of Edinburgh is one) that ericaceae (rhododendrons in Tod's case) are tolerant of ammonium-N but not of nitrate-N, so your theory is correct. Whether leafmould contains more nitrate-N than it used to depends, I suppose, on where it comes from as NOX deposition varies considerably with geographical location in relation to air pollution levels and rainfall amount and intensity (among other things). What is certain is that NOX deposition will be very low throughout Ireland for the aforesaid reasons, which will ensure that there has been no (or very little) nitrate-N enrichment of surface-level peat deposits there, whereas this might not be quite so certain for English or continental peats. Anyway, there is no doubt in my mind (nor in yours by the sound of it!) that leafmould is a poor substitute for peat as an organic compost ingredient for the fussier members of the ericaceae, such as cassiopes. There may be a middle ground solution in that I have found that good quality fine or medium grade composted forest bark (with the emphasis being on 'composted' and 'good quality') is almost as good as peat and better than leafmould made from leaves of broadleaved trees. Conifer leafmould is good, being more acidic than broadleaved, but the needles take ages to break down. An alternative if, like me, you live in an area where conifer plantations abound, is to visit one with a bag and collect the already pretty well decomposed needle mound after scraping off the upper layers of undecayed needles. What we do for the love of our plants!
Fascinating diary entry and discussion. One question. If you grow a Cassiope in pure peat how does it derive nutrition, as I always think of peat as being virtually nutrient free. Do you feed or is there enough nitrogen in rainwater to make the plant thrive?
The same must be true of sand beds and tufa, and I must admit to feeding plants in these for the first time, three or four years after making the bed. In this case though the roots often penetrate to much more fertile soil below, which makes such screes very effective. Ericaceous plants must be particularly well adapted to very low nutrient soils and their mycorrhizal relationships with fungi hugely increase the ability to access what nutrients there are. I need to re-read John's book!
It seems that even mentioning peat puts you into some anti-environmental camp, whereas probably the very opposite is true, and if John Kelly's article in the Bulletin years ago is accurate then horticultural uses of peat are a lot less significant overall than uses in power production - which of course generate CO‚??. Damage to vulnerable ecosystems is of course another thing.
Tim's response neatly sums up the situation regarding ericaceous plants and peat, you are much more likely to kill them by kindness than neglect, at least as far as feeding is concerned, and there is little doubt that rainfall provides all the nutrients that most ericaceous plants need, perhaps too much in areas with highly polluted air.
Regarding the moral question about peat use, again, I think Tim has got it right, they are still burning peat in large amounts in power stations in Ireland, Russia, and perhaps elsewhere, but that does not obviate the responsibility of those who know and care about such things to be concerned about habitat degradation, even if our hobby has a very small relative deleterious effect. I should hasten to add that I am in no position to throw stones as I still use peat, although in very small amounts, mainly for propagation.
Yes, as noted by Martin and Tim, it is amazing how little nutrient is needed by many alpines, and there is no doubt that high levels of nitrate-N is bad for many alpines, especially mycorrhizal dwarf shrubs such as Ericaeae, Diapensiaceae, Celmisias and many others. We have known for a century that many alpines thrive in a scree composed only of grit/gravel, or in tufa, and more recently the growing of alpines in pure sand has become fashionable and successful. The question is, 'from where do they get their nutrients'?. Mycorrhiza are not the answer, at least in inorganic media. I am sure that John is right that much of the nutrient does come in rainfall, or lateral water movement (snowmelt, springs etc). In most wild soils, phosphorus is usually the growth-limiting element, and phosphate levels are characteristically vanishingly small for much of the year, so that growth in alpines depends on a very short spring 'pulse' of soluble phosphate as it is released from insoluble polyphosphates by bacterial action. In this context, tapwater is particularly interesting, being typically much richer in soluble phosphates than rainwater or most (native) groundwaters. I wouldn't mind betting that much of the nutrient required by our Ericaceae, for instance, comes from occasionally use of the hose in dry weather, 'watering in' a new plant etc. In fact, I wonder if the nutrients in tapwater are actually too much for many of our slow-growing, nutrient shy alpines? Perhaps we should all go back to the use of rainwater butts to water Ericaeae and Diapensiaceae (as I know many people do for orchids).
This is getting really interesting, thanks John for this very informative contribution. I have to confess that I use only rainwater for all my watering needs, except in the most sever of droughts, which are not exactly a routine occurrence here in N. Wales! If you think of the growth that your average alpine, such as Gentiana acaulis, makes in a season compared with a dahlia, or even a bedding geranium, it is not surprising that they need so much less nutrients. As one brought up on the cultivation of herbaceous border plants (lupins, delphiniums, dahlias etc.)and vegetables, not to mention 'perfect' lawns, all of which require abundant supplies of nutrients, I have had to re-learn the hard way many times that alpines and orchids (and cacti) need very little in the way of feeding by comparison.