Observations on the Cold: Leonotis, Salvia and Rhodocoma – Pot Culture & Hardiness

Leonotis menthafolia x 'Savannah Sunset'

Leonotis menthafolia x ‘Savannah Sunset’ after Christmas still displaying its robust foliage.

Monday – Dec. 29, ’14 – low 33° – high 43°

Tuesday – Dec. 30, ’14 – low 28° – high 34°

Here’s one of my little experiments of ‘neglect’.  Sometimes the pots are just too big and heavy to haul down to my basement storage, not to mention the limited space there, so I position them up against my house, under roof overhangs, out of the wind and rain.  Many things I grow in pots, can take a few degrees of freeze overnight, but when we are supposed to have a period of prolonged freezing, when highs are forecasted to remain below the mark, I haul many of them in, otherwise outside they stay.   Then, out they go when it warms back up above freezing to a protected spot.  The pots in question, the biggest/heaviest, have been out all winter so far, sequestered under the roof on our deck.  They were not pulled in or covered during the first substantial cold snap and I’ve been surprised so far.  This is Tuesday noon-ish and it’s 34deg.

The Leonotis menthafolia ‘Savannah Sunset’, zn 8a, a name recognized by Annie’s Annuals, my source, but known by others as Leonotis ocymifolia var. ocymifolia, looks perfect and is still blooming at 5 1/2′ tall !!! silly plant.  Last year, with our two significant winter cold snaps, I lost one of these in the ground in a sunny exposed site.  That one received infrequent summer water and so was probably stressed going into last winter.  This Leonotis ranges from Kenya south into South Africa in the eastern half of the continent so it is somewhat more expectant of summer rains.  It prefers well drained soils.  This one shares a pot with a Cuphea ignea, zn 8, 9 or 10, (hmmm what’s the dealio?) which too is still green and blooming along with an unhappy Aeonium ‘Zwartkop’, zn 9, not blooming and looking a little peaked, no doubt suffering from too much shade in addition to the cold/dry provided by the roof overhang.

Salvia x 'Wendy's Wish'

Salvia x ‘Wendy’s Wish’ with a Cordyline ‘Pink Sensation’ poking out in the corner from another pot

The Salvia Wendy’s Wish, zn 9b, has lost many of its leaves, though the foliage that remains looks very good, and there is very little twig die back… You can see that it’s still happily blooming.  A note here, I often find it annoying when hybridizers conceal the parentage of their hybrids, as if I’m going to make the cross, grow thousands on to maybe find one with the same characteristics??? Who has the time or inclination?  No, I just want to know where they come from to help me make decisions for myself about their care.  This plant though was a spontaneous cross in Wendy Smith’s Australian garden of Salvia mexicana ‘Lolly’ sooo, without spending money on DNA testing, the male pollen donor gets to go on with his life blithely ignorant of his, in this case, daughter’s wonderful adventures around the world.  So, I have to let this one go!

There are many tender, for us, Salvia out there.  ‘Wendy’s Wish’ at 9b is hardy to 25°, or so some growers offer, while some Salvia mexicana (it’s female parent) selections are hardy to 8a, 10°.  This is quite a spread.  Knowing a plant’s provenance or at least its species helps us to best plant out our selection and tells us when we need to worry when the thermometer starts to plummet.  Do we bring it in, or just set it next to the foundation under the eave?  Do we wrap it in Remay out in the garden or make the effort to dig it and bring it in?  What about insulating it in place after wrapping it in christmas lights?  Or, maybe we should just take cuttings for next year and forget the plant.  If a plant is hardy down to 10° F, but it’s only going down into the mid-20’s….don’t you have other things you could use your time doing?  If someone is protecting their tender Salvia confertiflora hardy to 25°-30° F because it’s going down into the 20’s does that mean I should be protecting all of my tenderer Salvia, like Salvia apiana that can go below 15deg if it’s dry enough???Maybe, especially here in the NW if the soil is too wet (Mine’s growing next to the street at the base of a Trachycarpus that, if my plan holds, will draw extra moisture away from the Sage improving its cold hardiness).  Last winter’s two cold periods finished off my S.a. growing in my south facing concrete retaining wall.

Cold hardiness is about more than just temperature extremes.  How healthy is your plant going into the freeze?  Did it grow well during its active cycle last summer?  Was it able to grow long enough to flower and fruit…plants do have that nagging biological imperative of procreation pushing them.  Did it have enough time to ramp down its growth activity before the cold snap? or was it still pushing?  There’s a lot to think about.  For me, that’s one of the things that keep me interested.  There will always be other pretty plants and though I can be loathe to admit it, I find it easier now as I grow older to not chase after everyone and to spend more time on the relationships of those I have now.

Rhodocoma capensis

Rhodocoma capensis

The Rhodocoma capensis, zn 8a, spends its whole life in a pot.  It got hammered last year, because I was slow to protect it, and, subsequently, it has been slow to come back.  To be fair it spent most of the summer in less than 1/2 sun so I’m sure that didn’t help. (I planted a few of these in the Jefferson Circle bed of Waterfront Park a few years ago and they came through looking stellar last summer.  In the ground verses in the pot and a little heat island effect from being downtown on the river I suppose.) We’ll see how it does through this winter in the spring. I used to have two in tall ornate yellow clay pots until one got knocked over and broken, ouch:(  They made a very structural statement.  I miss that pot.  ‘Alas, poor Yorick, I knew him….’ One learns to move on.  I have another happy one in a 5gal pot that is revisiting the basement.  This is supposed to be the cold hardiest of all of the South African Restios (a family of grass like monocots).  A few years ago, I lost one I’d planted out in my clay/loam.

Rhodocoma capensis is native to the valleys of South Africa’s Cape Fold Mountains that abut much of the southwest and southern coastlines.  These are not the rich clay soil of the Willamette Valley, but are loamier, poorer soils with less rainfall.  These are plants of the ‘Fynbos’ not strictly limited to the Cape Floristic Kingdom as the many short mountain ranges that comprise the Fold spans the country east-west, being somewhat wetter in its eastern reaches.  The montane valleys are wetter, then the lower coastal Fynbos.   Both have a more mediterranean climate, especially in the western reaches of the Fold.  Don’t expect to find forested landscapes here.  Family Proteaceae is a dominate shrub/tree constituent of these valleys, with Erica predominating as you go up slope (There are more Erica spp. here than in the rest of the world combined).  It is notable that Proteaceae grow in phosphorus poor soils and are in fact intolerant of what might be a healthy level for most other plants.  As I said, these are nutrient poor soils.  This is the ‘Fynbos’ and family Restionaceae are frequent and often dominate residents of the ground level.  Rhodocoma capensis occurs most frequently in the more montane areas of the Fold.  So this is where we should look when in search of clues for growing it here.

Wednesday – December 31, ’14 – low 27° – high 37°

Leonotis menthafolia

Leonotis menthafolia on Wednesday 10:30 and 29°

I have to keep reminding myself of the specifics of our USDA zones.  Zn 6-7 are a no brainer, even for me.  With these plants I just have to keep their specific site conditions in mind and what typically comprises a species native community when I plant them out.  If I do that their survival is as close to a given as I’m going to get. Zn 8a and more cold sensitive, means that all of a plant’s requirements become even more important, because as I mentioned earlier, how well a plant is growing has much to do with the limits within which you can grow it. Zn 8a plants have an estimated bottom limit of 10-15° and 8b, 15-20°, 9a 20° – 25° and 9b 25° – 30°.  If they are struggling due to site conditions, they will fall short of this.  And, if they are growing in pots, they will be below this.  Of course you can often throw all of this out of the window if the zone designations are inaccurate, as they often are for plants relatively newly collected that have been conservatively tested in the landscape.  We learn, after all by growing these plants, noting their performance and…killing them in the effort as we establish their limits.  Growers, who are responsibly offering these to customers, will often err on the conservative side, in this case warmer, because you don’t want to doom a new introduction with unnecessary failures.

Populations and Provenance

Other hardiness issues arise when a plant is collected in one area within their natural range, are shared around the nursery industry and develop an in the ground performance history.  The industry and public come to know this plant in terms of hardiness and this becomes established.  Then someone else makes a new collection, from a different population occurring in a colder or warmer portion of its range so that when brought to market, the gardening community tends to plant it as they would have the earlier introduction.  Plants in the trade have a history and a kind of momentum and, because the public is slow to change, will plant it out as they would have the earlier introduction.  This can result in an inordinate amount of failure, followed by a hesitation on the part of the gardening public and a commensurate drop in sales, or, when the new selection comes from colder portion of a plant’s range, there may be a slowness to experiment in colder areas, because the public has come to ‘know’ this plant as tender for them.

Other times new forms of a species may be introduced, sports of species long established with unusual flowering habits or foliage and these individual ‘freaks’ of nature, may be more tender than their well know predecessor.  What all of this means is that as a gardener, there is more demanded of you if you are going to be successful.  Confusion may arise when gardeners, in an attempt to learn a plant’s limits, read of conflicting hardiness ratings for what appears to be the same plant.  Provenance, of the plant you have chosen can be very important.  This can also be important with regards to the specific growing conditions any given plant prefers, because this can range widely as well…but that is another story.

The gardener should also remember that named cultivars and even sometimes the species themselves are propagated asexually, not by the ‘lottery’ of seeds.  Seed grown plants contain within their genes the full range of conditions a plant can tolerate limited by the historical record of the particular population they come from.  Seedlings will individually ‘express’ themselves having tolerances somewhere within that range.  Seedlings from another population evolving historically under different conditions will ‘express’ these genes across their own unique range.  Seed grown plants mix the genes from within a defined pool, changing up each generation.  With a large enough population these plants with their wider gene pool are better able to adapt and meet changing conditions

With plants propagated asexually, there is none of this variability.  Each is a genetically identical clone.  Each is limited by the same genetic package and is confined to the same range of conditions within which they will perform.  Seedling genetic variability provides a species a broader opportunity to adapt and is the key to its long term survival.  No genetic variability seals the fate of a species.  If conditions change too much these will have less of an ability to adapt over time.  The industrial standardization of clones assures product uniformity and a consistency that most consumers seem to demand.  Plants that you can ‘plug in’ and have some assurance will perform as expected.  As habitat worldwide is converted to urban, agricultural or industrial use, species genetic diversity is necessarily reduced with the loss of regional populations.  We want to know what will this plant do in my garden or my pot and, so far, seem willing to give up the diversity.  We have chosen these forms for particular characteristics that appeal to us.  These are not necessarily the plants that would be most successful on their own in the uncontrolled environment.  But, really, whether your plant is a clone or a seedling, it is an individual and does not possess the full range of possibilities contained within the species and, you are choosing their location,…. As gardeners we have changed the landscape formula.  We are not nature dispersing thousands (nee, millions) of seeds across a landscape that they are generally well adapted to, successfully germinating and establishing in the ideal spot. The plants we use are products of horticulture and we have substituted ourselves for nature.  Our pots and gardens are the narrow view, but we need to understand that this is being played out on a world wide scale many millions of times.  This is, again, not just about some limited idea of plant hardiness.

Thursday – Jan 1, ’15 – low 28° – high 42°

Friday – Jan 2, ’15 – low 28° – high 44°

Leonotis menthafolia 'Savannh Sunset'

Leonotis menthafolia ‘Savannh Sunset’.  That’s a dead Lotus berthelotii parrot’s beak next to it.  Taken the following Saturday morning.


I checked our small, 2′ x 4 1/2′ x 18″ deep, kidney shaped pond this morning, 1/2″+ of ice…the freeze wasn’t that hard or deep.  It’s one of those molded poly pools so their are several gallons in it for freezing weather to draw the heat from.  By the time I thought to got outside to measure soil temps, at 12:30, it was already 42°.  There was no frozen crust on my soil and temps seemed to be around 33°.  My outside pots varied from around 33°- 35° the warmer ones containing a lighter mix, so drier, of course I’m not sure how accurate my thermometer is.  The predicted cold, that was to include more than 24 hours below freezing bracketed between four days of freezing nights with days just above, did not manifest.  It was cold, but not harshly so.  And, my Melianthus major, planted in an open site, still looks good retaining its foliage.

Sometimes I grow plants in pots specifically to keep them drier during the winter, whether Agave’s for more obvious reasons, or little plants like Begonia boliviense, which I’d lost several times growing in the soil under identical weather conditions.  Our cool wet soils may harbor fungi that are detrimental to some non-native plants causing them to succumb at temperatures above their expected minimum rotting out their roots and any below ground storage tissues like bulbs, tubers etc.   It could also be a response to the low oxygen in the wet clay soil many of us find ourselves gardening in here, or a combination…. When we bring in exotic plants there are many variables that most of us take for granted.  These plants did not evolve with the particular set of conditions that we have planted them into here.  Knowing this we should all be good little scientists and attempt to minimize the variables in our gardens, creating conditions we know they are more likely to have already experienced over generations.

Species, the genetic variability of the individual, provenance, overall health and vigor of the particular plant, whether a plant is in dormancy or in some active state of growth, temperature extremes, length of the freezing period and the regional peculiarities of the soil and the resident fungi…and probably more, can have a bearing on the ‘hardiness’ of your chosen plants.  It is not just about the temperature.

Salvia 'Wendy's Wish'

Salvia ‘Wendy’s Wish’

The result of this second cold ‘snap’ appears to be minimal to the potted plants in question here, including the Salvia ‘Wendy’s Wish’ which was subjected to four nights into the lower limit of it’s zn 9b designation.  It is an interesting characteristic of many ‘tropical’ and ‘sub-tropical’ plants that they don’t have a cold response, except to die at their limit.  These plants tend to look ‘normal’ right up until they die and don’t begin shutting down, like temperate plants, as the average temperature drops.  9b would appear to be a conservative hardiness rating, but it could also be that 2-3 degrees colder could have flipped the switch on it.  All of the others, the Leonotis zn 8a, Cuphea zn 8-10(?) and Aeonium zn 9, appear to be relatively unscathed.  The Leonotis and Cuphea still retain the flowers they went into the snap with.

I thought I’d throw in here a mention of Aloe saponaria which I grow in pots and in the ground. I’ve grown it for ten or more years holding a few pups in pots for the winter and/or keeping one in a display pot to assure its annual flowering, but I’ve also kept one in the ground on a south facing bank, though it’s toward the bottom of the slope where the unamended soil gets quite wet above the sidewalk (the top portion of the bank being naturally better drained).  IMG_1398

The current garden resident is a survivor of our previous streaky, harsh/ mild, winter, having completely died back but had enough energy, and good tissue remaining, for it to resprout in several places.  I was unsure how said survivors would do so I popped in a new one in the center.  The picture is current and you can see a few slightly darkened leaves on the main plant which is a tell that they have suffered damage from our previous cold.  All in all, it looks pretty good and I’m crossing my fingers that it will continue intact and flower early this coming summer as it does when it winters over.

Interestingly, during the first week of January ’04,  we had a very similar cold snap only the temperatures in fact were similar to what were predicted for us this time.  We had 3-4 days around the area with highs below freezing.  Some gardeners remember it as the Phormium killing year.  I lost several plants that had been ‘tough’ for me for a number of years.  Yet other things, I had worried about like my newly planted Butia capitata, 3″ dia. at the base, survived with the aid of having been wrapped in fiberglass insulation and a tarp.

It is true that many evergreens, especially those with very substantial leaves like Grevillea, can sustain cold damage without showing it until growth initiates in the spring, I’ve had a couple of Grevillea, like G.’Canberra Gem’ suddenly shed their leaves and give it up later in March long after the freezes, the plants discussed above have softer, fleshier foliage, which tends to show damage more immediately.  I think, so far for this review, these plants are good, of course depending on what the rest of the winter brings.

One thing I would hope that readers take from this entry is the complexity of cold hardiness and the idea that whether a plant freezes or survives for one person is neither indictment nor guarantee for how the same plant may perform for you.  There are many variables.  Gardeners should take these events as an opportunity to evaluate their own practice.  Without doing this we will miss many opportunities for success simply because we chose prematurely not to take the risk.  Conditions vary widely from garden to garden even with the same City.  Understanding your own site and the requirements of the plants that you consider is part of becoming a better gardener.  Choosing to do only what your fellows have done successfully may seem ‘safe’, but is no guarantee.



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