converting ºC to ºF or ºF to ºC

David Ehrlich
Mon, 09 Feb 2009 14:05:24 PST

A little trick I learned in Hight School:
  Add 40º
  multiply by 5/9 or 9/5, depending upon which way you want to go
  Subtract 40º

This rule is far easier to remember than any other.

From: "" <>
Sent: Monday, February 9, 2009 9:59:50 AM
Subject: [pbs] seed sowing - timing of

I find the exchanges here are always fascinating for numerous reasons not the least of which to some degree or other we are all probably slightly mad, in the nicest possible way of course. It seems the parameters under which various people strive are often wide ranging, both bio-geographically as in plants orininating from Northern and Southern Hemispheres as well as Maritime, Continental and Montane climatic ecosystems and just to sow yet more self inflicted confusion, Arid versus Humid.

For what little worth or interest it may be, here at ABG I sow seed of some 250 - 300 taxa annually. Of necessity the genera being worked with are from north temperate, boreal, alpine / arctic climatic types. However, in practical terms the local climate here is borderline maritime / continental [just] = roughly to USDA Zone 6 to 7 but an added aspect which I don't see referred to in any questions and answers in relation to seed sowing.timing and so forth is any awareness of latitude effects that definitely have a bearing on seed germination amongst many genera. I function here effectively at 58 degrees North which puts me in terms of lux levels = day length and intensity, modified by cloud cover percentages at a different level of influence than say somebody trying to work with temperate genera in what is effectively a Mediterranean climate to a huge extent in say California, [ central and southern coastal ] and the analogues with European Balkan and
 Apennine mountains and S
outhern Alps in terms of your mountain locations. In other words we have almost total daylight allowing me to read a newspaper at midnight at mid summer to very low lux levels in the winter when the world is either grey or white for a few hours dayly. Right now here in early February we are getting darkish at 4 pm, we had - 18 C last night preceeded by 60 cms of snow on top of a previous fall a few days previously.

I admire your collective courage but am staggered by the hurdles you often appear to inflict on yourselves in some of the plants you try so hard to work with when they clearly are not suited to natural processes in such areas in so many instances. I can't do the calculations any more converting from Centigrade to Fahrenheit as we left that behind long ago with the rest of the world and my memory is pretty rubbish anyway, however there is a crude rule of thumb for temperature clines which runs roughly as that for every 100 metres of altitude there is a drop of 1 degree Celsius with intuitive allowances for aspect, i.e. north versus south on a slope, the latter being moderately milder than the former. Presumably someone will have access to the conversion factor between Celsius and Fahrenheit. Mention Fahrenheit here in Europe and the rest of the world pretty much and they look at you as if you as if you have some sort of affliction so I don't know where to
 go to do so but good 
old Google might well be of help.

In general terms, temperate and boreal species, e.g. amongst Iridaceae and Liliaceae are best grown by sowing the seeds as mother intended, i.e. immediately they are ripe because so many need to be vernalised before breaking dormancy or become dormant and if not they will lay for one or two years before germinating if left until the spring. Both are an evolutionary survival strategy however we can't all get our seed as soon as its fresh especially when coming from a different hemisphere. Two final aspects I haven't seen referred to but may well have missed are [a]  the influence of light on germination, some seeds discriminate against lux levels of any sort and will be inhibited in germinating, other seeds positively discriminate in favour of the need for lux levels at the right amount over a specific period in order to germinate, indeed soem lily seeds will germinate inside a fridge in the dark !; and [b] the fact that as far as I am aware, every plant
 has an endogenous rhyt
hm, i.e. their seed will, as in the case of the plants leaving dormancy, initiate growth / germination in response to a heat sum which for example in many Temperate and Boreal trees and shrubs is, put very crudely, around 8 degrees Celsius per day time 'x' days at 8 degrees an admittedly broad brush generalised statement qualified by research based per individual genera. From the work I am doing at the moment on Lilium it seems that this may also hold true but there is more to be done and I haven't yet had time to analyse the figures recorded so far.

To illustrate the above, from my silvicultural days, we grow here a north - south cline of Silver Birch - Betula pendula, starting with trees from the most northerly place in the world where arboreal trees grow, i.e.  Nord Cape in Norway straight down through Europe to a southern population of the same species from just north of Madrid in Spain. It is fascinating in Spring watching the leaf burst progress along the line of these trees as the heat sum accumulates and in reverse along the line watching onset of senescense in the Autumn. I suspect some of the problems folk are coming up against may be due to not allowing for or being aware of these, several or various, parameters to germination of their seeds.

I hope one or two of the above points might through some light on the subject and be of some help to somebody.  Iain

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