Prepping outdoor cacti and agave for winter

A cold snap came to the Eastern Plains of Colorado (Zone 5) recently, with plenty more on the way. By now the leaves are mostly off the trees and, with the exception of the oddly-hardy parsley out back, almost all the other plants are either dormant or dying.

That includes the cold-hardy cacti and agaves that I have. This is the time of year to start getting them ready to cope with the cold.

In reality, though, that prep starts back when you first plant them. If there was one thing to share with you about cacti, coming from a man who has killed more than his fair share of them, it's this: cacti and agave absolutely, positively do not tolerate being wet for extended periods.

You can get cacti that tolerate cold, you can get them that cannot, but all of them will rot and die if they get wet and stay wet.

Your first job then is to make sure that they stay as dry as possible.  My soil out here is brick clay covered by a thin skim of topsoil, so all my cacti live in what are effectively raised beds or pots, with my own not-so-secret recipe cactus/agave soil mix (email me at info@goodthingsfromcoryskitchenandyard.com and I'll share).  This is the first line of defense as the thin, quick-drying soil will let any water slide on by and dry quickly.

Second, you need to really be careful about how much water they get after about mid-August.  You want your cacti and agave scooting on into winter a little dehydrated.  This is not usually a problem out here on the plains, but if you live in an area that gets lots of water in the transition seasons, you should think about covering them (see below) a little early so they're not accumulating water just in time to start freezing.

Third, for cacti that are on the edge of being hardy enough for you to keep outdoors all year long, or if you want to take out some insurance, use a trick that I had someone suggest to me:  make yourself a "microclimate" by burying a big rock and planting your cactus/agave next to it.  The big rock can act as both a shield against harsh winds and as thermal ballast.  It will soak up heat from the sun all day and then give it back at night as temperatures fall.  Depending on the location and orientation, try to shoot to have your cactus on a south facing side of the rock.

So, if you've set yourself up for success with the above, now it's time to start talking about winter prep.  Let's talk expectations first.  Your cacti will start to shrivel and look dead, but they're not dying.  I remember my first year trying to grow cacti year-round outdoors.  I thought I had killed them all!  I left them in the ground, desiccated, wrinkly, and shrunken as they were.  I figured what bits lived would live and that I'd deal with that later..  Come Spring, I was able to relax as they plumped right back up.  Point is, don't freak out and do something like water them or dig them out. 

 Keeping your cacti dry (and agaves slightly warmer) continues on into Winter.  Some of my cacti are natives from friends' land.  They're used to living out here and thus I don't worry overmuch about covering them or making sure they have a warming rock.  The one thing I do watch with them is making sure that they stay clear of leaves and debris.  Where they come from there aren't many deciduous trees like there are here in town.  If the leaves piled up, they'll get wet and stay wet.

For those that are more sensitive, I make a cover, surrounding them with something that is waterproof and also perhaps slightly insulating.  Old milk bottles with the bottoms cut off and some holes punched in them work really good here.  You can slip the bottle over the cactus and then put yard staples down through the holes you punched so the bottle stays put in the wind (something critically important out here on the windswept Colorado plains). 

Leave the top off the bottle during the early part of Fall/Winter, cap it and leave it capped during deepest darkest winter, and then uncap it come early Spring.  You want those plants dry, not cooked!

I'm experimenting this year with that mylar-faced bubble wrap insulation that I had left over from a previous project.  I made some conical hats of various sizes, cones being a pretty easy shape to fabricate from scrap.  For future years when the cacti are bigger, I may look at getting insulated clear cups and/or perhaps some small-ish coolers.  As I say above with the milk jugs, be careful on warm days!

Lastly, accept that some cacti just cannot be left outdoors over the winter.  Doesn't make them bad, it just means they'll need to be in a permanent container home like my friend blue gumby.  He loves being outdoors (growing like a weed) in the summer, but will not tolerate cold.  I treat him just like the others, though.  No water after mid-August and bring him in (with perhaps a grow light since my house tends to be pretty dark).

I hope this was helpful.  If you are thinking about growing cacti in cold climates and leaving them outdoors and you want some tips, book some time with me and let's talk!