The Garden Professors™

Back in February I had the opportunity to give a talk on a new book that I put together with a friend of mine, Meleah Maynard, who is a Master Gardener and garden writer here in Minnesota (you can see our promotional video here  — this is the video our administration let us run — you should have seen the one they didn’t!).  We conducted this talk at Bachman’s — a very well known garden center here in Minnesota.  For this talk we took products off the shelves and talked about them — some we trashed, like high phosphorus fertilizers.  Some we raved about, like cotton seed meal.

Anyway, Bachman’s got word of what we’d done.  How could they not?  some of their employees were there –and they loved it.  In fact, they brought me, as well as some internal people and John Lloyd — a well known and well respected tree guy in the area — back to talk to their sales force about the good and bad products they carry.  No holds barred.

This is the kind of thing I love, and here’s why.  I’m pretty difficult to pin down politically.  On some topics there’s no doubt I’m a liberal, on some a right winger.  Sometimes to the point of being a libertarian.  When it comes to garden centers I’m a libertarian.  Companies needs to make money, so they should have a diverse inventory, if that’s what brings consumers in, and let the buyer beware.  Part of Bachman’s success comes from the huge variety of products it carries, and I think it would be a shame for them to reduce this variety in any way — it could hurt business.  HOWEVER, Bachman’s knows that this freedom doesn’t mean that Bachman’s employees should be ignorant of the environmental consequences of some of the products they carry, or that they should recommend these products to their customers when asked.  So they have the best of both worlds — If you want some nutty product, hey, Bachman’s has it, and if you really want to know which products are good or bad?  Hey, just ask their knowledgeable sales force.  Nice!

On this blog we get mad at lots of things.  Sure, anger is fun, but sometimes you’ve got to suck it up and say something nice for a change.  So today I thought I’d point out a product that, while it comes from a company that I’ve had issues with in the past, is, itself, a good product.  I like Miracle-Gro Moisture Control potting mix.  The reason is that it utilizes coconut coir, a waste product from coconuts which holds lots of water and which can still maintain good aeration.  That means a reduced amount of peat.  I also like that the fertility present in this product (so you don’t need to fertilize right after you plant) is 3-1-2 which is appropriate for most situations.  Now, could you mix up you own coir potting mix more cheaply?  Sure, if you can find it.  You could also fertilize with a renewable organic fertilizer.  Still, I think Miracle-Gro got this one right.

Last week I decided to continue my discussion on cold hardiness and so now, of course, temperatures are forecast in the mid-70’s for this week.  Oh well, I’m still convinced we’ve got one more blast of winter to go and some of this will still matter to someone.

One of the questions posed in response to last week’s post was how much cold hardiness changes during the winter.  Before I get into that, it’s good to review how cold hardiness can be quantified.  Cold hardiness is essentially how much cold a plant can withstand before it suffers damage.  There are two common ways by which this can be measured.  The simplest and most straightforward method is through a whole plant (or whole shoot) freeze test.  In this test, entire plants, usually seedlings, are placed in freezer that is programmed to drop the temperature progressively colder, say from 3 deg C to -36 deg. C

At set intervals, often 3 deg. C, a group of plants are removed.  The plants are allowed to slowly thaw and are then examined for needle damage or bud kill.  At the warmest temperatures, plants are undamaged.  As we examine plants subjected to colder temperatures, we’ll begin to find some with damage.  Eventually we’ll find a temperature where all the plants are damaged.  When we plot the percent of damaged plants versus temperature we can identify an LT50, or lethal threshold where 50% of plants are damaged.

Examples of determining bud damage during whole shoot freeze tests.

The second common assay for cold hardiness is termed Freeze-induced electrolyte leakage or FIEL.  FIEL testing is similar to the whole plant freeze test except that instead of freezing the entire plant or shoot, just a small portion of tissue, such as a conifer needle segment is needed.  The FIEL test is based on the fact that plants can withstand inter-cellular ice (ice between cells) but not intra-cellular ice (ice within cells).  When intra-cellular ice forms it disrupts the cell membranes and cell contents are released into solution.  The amount of leakage of cell contents into solution can be easily measured using a standard conductivity meter.  Again, we can estimate an LT50 by plotting the amount of damage versus exposure temperature.

By assessing cold hardiness periodically through the winter, we can assess changes in hardiness associated with acclimation and de-acclimation processes.  A classic study by Karen Burr and her colleagues demonstrates how quickly acclimation can change.  In their study they tracked cold hardiness of conifer seedlings that we exposed to acclimating conditions (short days and progressively colder temps) and then de-acclimating conditions (longer days and warming temps).  The resulting chart demonstrates how dynamic cold hardiness can be.  When we describe plans based on Hardiness zone we’re talking about their maximum hardiness or the temps they can stand in the mid-winter period.  But note how quickly the lethal temperature rises during de-acclimation.
Seasonal trend in phases of cold hardiness: Acclimation, Maximum hardiness, and De-acclimation

Typically, our most common winter injury problems occur during the de-acclimation phase as temps warm and hardiness is lost.  We saw a dramatic example of this several years ago in western Michigan when an early March warm-up with temperatures in the 50’s F was followed by nights with temps as low a -5 deg.  This resulted in widespread bud-kill in conifer plantations.  With a week of highs in the 60’s and 70’s forecast, it’s easy to see why our current warm-up has everyone nervous.

Maximum and minimum temperatures from a west Michigan weather station