Fertilizers, crops and landscapes

Last week Jeff wrote about the dangers of using “balanced” fertilizers, especially in reference to phosphorus content.  Comments quickly followed about using fertilizers in many situations – on farms, in container plants, on trees – and so on.  One of the latest comments came from Nick and began “I don’t usually recommend fertilizer for perennials or woody plants to consumers. In most cases they aren’t needed.”  And this leads into today’s topic.

Many of the horticultural practices we use in our gardens and landscapes have, unfortunately, been derived from agricultural crop production.  Whether you’re growing a field of wheat, garden tomatoes, or containerized shrubs your goal is maximizing crop production.  By its nature, this is an unsustainable practice because it requires continual inputs of water and nutrients at higher levels than would naturally occur.

But this is not how you should care for landscape trees and shrubs, and why Nick’s comment was a good one.  You don’t need to routinely add fertilizer to these plants; they don’t need it to grow normally.  What we should be doing in landscapes is preventing nutrient deficiencies.  Once you have a soil test in hand, you’ll know what nutrients may be too low (or too high) and how soil pH will affect that.  For most of us, this may involve occasionally adding one of a few nutrients (most commonly nitrogen), or perhaps acidifying the soil to improve nutrient availability.

 How do you know when to add nitrogen to established landscape plants?  Let your foliage do the talking. If leaves are uniformly yellow, small and sparse, you might have a nitrogen deficiency.  This will be most common in the mid to late summer, when plants are growing most rapidly and competing with one another for resources.  Be sure this symptom is wide-spread, however.  If it’s just one plant showing deficiency symptoms, it’s probably not a landscape issue.


Cirque du Poinsettia

Last week I brought up the seasonal topic of poinsettias. There are so many cultivars to start with, it’ll make your head spin.  Twenty five new varieties were introduced in 2009 alone.  One
of the major breeders lists 36 RED varieties.

But for painting and glitter, growers
and retailers stick to “white” (actually a very pale yellow to cream –
see last week’s ‘Polar Bear’ post) or possibly light pink. The trend had a good start in Europe and crossed the pond in 2004. I

n 2005, I toured a Denver area greenhouse and saw my first air-brushed point. They were doing a specialty Broncos theme with bracts sprayed deep blue and orange and plopped into a football-shaped pot (with the season Denver’s having this year, I imagine sales are down).  The “team colors” theme is everywhere now.  Nothing says Christmas like maroon bracts (looked more like dried blood) with orange glitter – the interpretation of a Hokie poinsettia, available at our local Kroger. Different.  Please comment if you’ve seen a weirder color combo (are there Steelers ones yet?!).

Nationally, independent garden centers note they can’t keep pigmented points in stock, despite charging upwards of $9 more for a painted 6” point than a regular one. 

I'll have a bluuue Christmas without yoooooou

Blue poinsettias at McDonald’s Garden Center in Virginia Beach – a best-seller.

I’ve not seen any studies determining if the dye alters the post-harvest longevity or not; anecdotal evidence suggests it doesn’t have much effect. Just don’t splash them with water – the dye will run. Growers are careful to paint only mature poinsettias with fully-expanded bracts, or else suffer the poinsettia equivalent of bad roots (a la Lindsey Lohan). One of best-known of the poinsettia painters is at K&W Greenery of Janesville, Wisconsin.  The owners have carved out their high-end niche by employing an artist to do the air-brushing and glitter-sprinkling, treating each one as an individual work of art.  Art that will die in a heartbeat if you forget to water it, unfortunately. But the mother of all poinsettia growers/retailers in Ellison’s in Brenham, Texas. They’ve turned the season’s opening  each year into a hugely successful, candle-lit, wine-pouring party. The Today Show even stopped by a few years ago. The Ellison’s tree photo has been making its rounds on the internet for so long, I don’t even know who to credit.


Where's the damn partridge

Fa la la la la  (is that enough “la’s”?) 

Whether you take your poinsettias painted, straight up, or not at all – happy holidays!

Saving your ash

My earlier post regarding plans to replace the monoculture of ash trees at the Gateway Arch Monument in St. Louis, MO with a monoculture of Lindens prompted a question about options for treating ash trees for emerald ash borer.  This is a complex topic so I wanted make sure I had time and space to respond completely.


First, the best and most current source of information regarding treatments for EAB is the Multi-state bulletin “Insecticide Options for Protecting Ash Trees from Emerald Ash Borer” which is available as a full-color .pdf on the EmeraldAshBorer.info website.  Anyone who lives in or near EAB-affected areas and is considering treating their ash trees should take the time to download and read this bulletin.


Here are some key points to consider if you want to save you ash:

It is possible to protect ash trees from EAB with insecticides.  There are several examples in and around the original core infestation area in Detroit where arborists have successfully protected trees since EAB first was identified in 2002.  There are two general options; protective cover sprays and systemic applications.  For most trees, protective cover applications will require professional application with specialized high-pressure spray equipment.  Most systemic application will also need to be applied by professional applicators, except for small trees that can be treated with soil drenches of systemic insecticide.  To date, the most effective systemic product is emamectin benzoate, sold under the trade name TREE-äge.  In various tests, emamectin has shown the highest level of control among products tested and is also the only product that consistently provides more than one year of control.  Imidacloprid is also effective as a systemic but will need to be re-applied annually for the best level of control.


The likelihood of successfully treating an ash tree declines rapidly once trees begin to show noticeable crown-die-back.  In certain cases, researchers have been able to save EAB-infested trees showing some crown die-back, but once 50% of the crown is affected the tree is likely a goner.


Once started, treatments will need to continue in perpetuity.  To me, this is the biggest factor homeowners need to consider if they’re thinking about treating their ash trees.  To the best of our knowledge, EAB is here to stay.  EAB populations may begin to decline once most of the ash trees in a region have been wiped out, but trees in woodlots and forests that have been killed will continue to sprout, providing host material to maintain an endemic population of beetles for the foreseeable future.  Systemic applications can provide control but the products will need to be re-applied every year (imidacloprid) or every other year (emamectin) to be effective.


Effectively treating trees larger than 4” in diameter will require applications by a certified pesticide applicator and may cost several hundred dollars per tree.  Homeowners need to carefully consider the cost of on-going treatments versus removal and replacement.


Mention of trade names does not imply in endorsement.  Read and follow label directions when applying pesticides.

Friday puzzle unrolled

I knew this one was pretty easy, but I have my reasons (below).  Gold stars to KB, Jim, John, and Dave for correctly identifying rolls of sod (and they do seem thin, Peter):

Yes, sod.  I dislike instant lawns; they never look good for very long, at least in my part of the country.  And getting rid of sod (as we have in our landscape) is a nightmare with that *%&$^ plastic mesh in which the grass is embedded.  It breaks up into little bits that are constantly coming to the surface.

I don’t have an axe to grind about lawns; my philosophy is that if you want a lawn and can afford to maintain it well, more power to you.  But what’s wrong with the old fashioned way of seeding a lawn?  Sure, it takes a few more weeks to "grow your own", but seeded lawns look more natural and last much longer.

Balanced fertilizers are usually out of balance

I’m in the midst of grading papers for my nursery management class, and something that I’m running across is an incredible number of papers where the students are recommending balanced fertilizers.  Why are they doing that?  Or maybe an even better question is, what is a balanced fertilizer?  A balanced fertilizer is a fertilizer which has three numbers which are about the same, like a 10-10-10.  The problem with balanced fertilizers is that they are much higher in phosphorus than what most plants need — at least in relation to the amount of nitrogen and potassium which plants need.  Especially here in Minnesota, where there is usually plenty of phosphorus in the ground, this extra phosphorus serves no purpose except to pollute waterways.  We have got to break the cycle of just assuming that a balanced fertilizer is the way to go.  I get to see a lot of soil tests from old agricultural fields where balanced fertilizers were used for years and years.  Usually 10-10-10.  What I usually see — with very few exceptions — are phosphorus and potassium levels which are either very high or off the charts entirely.  Phosphorus and potassium don’t move readily in the soil while nitrogen does, so every year that you add 10-10-10 in the appropriate amount for your plants needs for nitrogen you’re adding too much phosphorus and potassium.  Any extra nitrogen which you add will move through your soil, but P and K will build up year after year (and some will run-off into gutters and drains).  So what do I recommend?  I like a ratio of about 5-1-2 or 5-1-3 for an N-P-K ratio in a general use fertilizer.

Snow falling on cedars…not always a good thing

Seattle had its first snowfall last week – a mere 3-6″ – and the city shut down.  (Yes, those of you in the snowier parts of the midwest and east can laugh…but we’ve got hills.  That’s the main problem.)  It was unusally cold, so the snow that fell was the light, fluffy kind that I remember from our Buffalo years.

Every year someone writes to ask whether they should remove the snow from their trees and shrubs.  Here’s what I suggest:

1)  If it’s very cold and the snow is dry and light, I advise leaving the snow on.  It serves to insulate tissues from freeze damage.

2)  If the snow is wet and heavy (i.e. temperatures are not that cold), you should remove as much as possible.  The insulation isn’t necessary, and the weight load can permanently damage trees and shrubs.

This damage can’t be easily repaired; the only alternatives are to cut bent trunks and branches out entirely (no stub cuts!), or to tie them up.  Not being into plant bondage, I generally cut bent branches away.