Following is a list of the species as they stand now. Each species plant was visually observed and then placed into one of three categories (1/ growing perfectly; 2/ some damage showing; 3/ poor growing and turning brown). We have received the remark that the pale green yellowish leaflets with the darker veins might also be a result of magnesium deficiency. Possibly, but all plants are grown next to one another in the same soil and some species show this whilst others totally not whereas the difference has also only recently come to be, so we currently don't think this is the cause. We don't have all species and observations are made on only one or a few plants at most. Some may be wrongly labelled and there will be differences between individual plants within a given species or population. There are also differences between seedlings and mature plants, the latter able to cope longer with drought. We also have some species growing outside in our normal fields, which receive full sun but where the soil is less dry, those have not been taken into account as the comparison here is for drought tolerance. So there are many remarks and possibilities for errors, but we do hope it can still be of interest for those wanting to grow peony species. And for us it is interesting in that it gives us some guidance as to what species to use in hybridizing.
As could be expected the species that naturally grow in places that experience dry and hot weather in Summer seem to cope better than the others. Those are many of the Mediterranean ones: P. cambessedesii, P. corsica, P. morisii, P. sandrae and P. broteri for example. Those species are growing perfectly fine despite the dry conditions.
The reverse is also true of course, peonies that grow further North, seem to have more difficulty, P. anomala is a good example.
Then there are the peony species that grow in areas that receive less rain, the so-called 'steppe' peonies like P. tenuifolia or P. hybrida, they are obviously well adapted to these circumstances.
Peony species that grow high in the mountains in nature seem to have more problems: all species in the wittmanniana group are in this case. P. tomentosa, P. wittmanniana and P. macrophylla are all showing lack of vigour and are slowly turning paler green and yellow. The best of these three seems to be P. tomentosa.
Between some closely related (or close by growing) species there are sometimes differences as well. The P. officinalis group, which is spread over a huge territory from Portugal over Spain, France, Switzerland, Italy and former Yugoslavia has representatives coping better than others. P. officinalis ssp microcarpa (aka P. villosa) copes very well, whilst the same can be said of subspecies italica and officinalis. The Southern France subspecies huthii and more Eastern subspecies banatica seem less tolerant of drought. Another difference exists in the so-called 'daurica' group. Whereas the Crimean P. daurica ssp daurica grows fine, the more Southernly growing P. caucasica has more difficulty. Of course P. daurica ssp daurica has more upfacing leaflets that direct the rainwater on the leaves towards the base of the stems and thus the roots. P. caucasica on the other hand has more flat or downwards facing leaflets that drain that rainwater away from the base of the stems. That difference is probably an adaptation to the the regions they are growing naturally with Crimea receiving far less rain than the Eastern Black Sea region. Two other close species are P. obovata and P. japonica, here at least it can be seen that P. obovata copes better with drought than P. japonica, although it would be unfair to classify even the former as drought tolerant. Another duo: P. peregrina also seems more tolerant than P. saueri. And within that other widely spread P. mascula species, it turns out that subspecies russoi and hellenica are far better than bodurii and mascula. Here it must be stressed however that bodurii is far easier to grow than hellenica, the latter not able to cope with wet circumstances, which is obviously the other side of the medal and which is probably also true for the species we lost last year.
Some that are perhaps a little bit unexpectedly doing poor are P. coriacea, P. mascula ssp mascula and P. turcica. Those are already turning brown. It doesn't necessarily mean they can't handle dry circumstances as they may simply be genetically inclined to do that this early. But it is obviously not a very pretty sight and if the leaflets are not green, then the roots will not increase during Summer also. P. wendelboi, despite it growing in a very dry location naturally is another one which was unexpected. It could of course be that I have a hybrid between P. mlokosewitschii and P. wendelboi, which could explain this as P. mlokosewitschii does not grow in such an arid climate. On the other hand I have several plants from a controlled cross, if the mother plant were a hybrid, then the seedlings should show much more difference (in height for example), which they don't, so this actually points to it being true-to-name.
With the limitations mentioned above we would welcome any additional comments on your experiences with peony species and drought tolerance (or the reverse, how do they cope with wet Summers). We can then add those remarks to the table. The comments section below is for you ;-)