Helping hand at the zoo

TPP was offering a helping hand to a local zoo. Oh, it had nothing to do with the animals, but the landscaping of some exhibits being built and planned. Here's the rub, you're not going to have authentic Australian plants landscaping the area around a wallaby exhibit. The hard zone 5 climate here in the upper midwest USA very much limits your landscape choices to plants from similar climates. That pretty much leaves Australia out. Too bad, TPP would love to have a tree fern or two, or maybe a Wollemia nobilis. No gum trees, no grass trees, but perhaps a cycad in a planter box so it could be moved inside for over wintering. There was a time when TPP had house-sitters who left his cycads outside for the winter. That only happened once. Sigh. Actually many zoos are quite interested in getting and keeping plants. Hardy bamboos were discussed, and curiously the spreading habit of some is not a liability when the prunings become animal fodder in a sort of "grow your own" plan. Kroger bamboo is always so expensive. It was actually quite a bit of fun, and some rather bad suggestions from their architect who obviously didn't get any horticultural help were improved upon. The zoo people found it amusing when TPP pulled out his much used, much annotated, much stuffed with labels copy of Dirr, and if you have to be told what that is, then you are not a serious gardener in these parts. Why, Dirr is the woody plant Bible of the upper midwest.

Plant cold hardiness - It's the extremes, people!

When it comes to plant distributions based on temperature, it's the extremes that determine the limits.  Unfortunately, there also is a lot of misinformation, some might call it fraud, in the nursery business.  Now understand, there's a big difference between a plant that is hardy to zone 6 versus one that is hardy in zone 5, about 10 degrees (F) of cold tolerance.  And a lot more territory in which to sell a plant labeled zone 5.  TPP remarked in a workshop presentation that cedars (Cedrus) are not reliably hardy in zone 5.  A woman replied that she bought a Cedrus libani (cedar of Lebanon) that was labeled zone 5, oh yes, and it had died this year. According to a very authoritative source, one variety (var. stenocoma) is supposedly hardy "in the warmer parts of zone 5", which ain't here!  There is a lot of north-south territory in this part of zone 5 in the great Midwest.  The tree in question had been planted 4 years ago, and for the past three winters our minimum temperature has been about 0 F (32 degrees F below freezing for the rest of the world), but this year we've had temperatures below zero weekly for two months reaching a minimum of -17 F, nearly two cold hardiness zones, near the minimum expected temperature for zone 5 (-20 F), and certainly not in keeping with being the warmer part of zone 5, which is probably about 100 miles south of here. Even then how confident can you be that the tree in question was the "hardy variety"?  To label such a tree as hardy in zone 5 is a fraud.  This species of cedar prefers a zone 7 climate, but can handle zone 6, and with little exception, is not hardy in zone 5.  Now TPP regularly plants things that are zone 6 plants, and just as regularly some of them die, but not all.  Unfortunately because cedars are wonderful trees, cedars don't appear to be one of the tough ones. This winter will sort out the real cold hardiness.  One of TPP's range extension plants is Helianthemum (Cistaceae), a good Mediterranean shrub. Hopefully the snow cover has protected this low-growing plant, and the bunnies have ignored it. Some plants will die back and re-sprout from the base (e.g., Vitex). A sweet bay magnolia was struggling, and was replaced by a hardier variety, and hopefully it will survive.  Generally, it's best to select plants grown north of your area.  Plants grown further south are a poor bet; northwestern grown plants are nearly always losers.  It's like Californians that move to Chi-town. It is to laugh. Always ask about the nursery source. So while really cold winters are becoming less frequent, as you would expect with global warming, the extremes have not shifted northward as yet, so you pays you money and you takes you chances.

Cold and plant hardiness

It's been cold, seriously cold, and while restating the obvious, it perhaps prompted a reader to ask about the effect of extreme wind chills upon plants.  OK, this is an easy one; wind chill doesn't affect plants.  Only the absolute temperature matters, not how the wind makes the cold feel to us and other animals. Recently our absolute temperature hit -17 F (-27 C), and this is very near the rock bottom hardiness for zone 5 plants. In TPP's 35 years here in northern Lincolnland, the coldest it has been is -19 F. This is the absolute limit for freezing-avoiders, a topic discussed before. Until spring you really don't know what damage has been done to what plants.  Some tender woody plants will die back, and many will sprout from the base, so be patient before cutting things back.  Our Vitex (chaste tree) will certainly be in this category.  Over the past couple of years all of it survived the winters and it had gotten 2.5+ m tall.  My Mother, a native southerner, had a pet mimosa tree in upstate New York that survived because it was planted where the ample snow fall always drifted providing it with insulation.  Granted the mimosa never grew much taller than 4 feet, but she like it anyways and in bloom it often stopped traffic.  So snow cover makes a big difference, as does mulching.  This year the deep cold came with snow, so low growing things and herbaceous perennials will probably be largely undamaged.  In a few cases TPP is worried because either he or the nurserymen were cheating by planting marginally hardy plants (TPP) or over stating the hardiness of some plants (a lot of plants labelled zone 5 on nursery tags are not so rated anywhere else).  OK, so you gamble.  But it will be another 4 months before the data can be collected about what was damaged and what was not.  Another problem associated with this is that winter kill is more often about dehydration, especially of evergreens, both conifers and other types, than it is about cold.  If you stopped watering newly planted evergreens when the weather got cooler, and drier, then you put them at risk.  Again, mulching helps greatly.  Now stay tuned because next TPP will explain about frost cracks in trees and why it happens and why it doesn't.