Planting trouble: multiple trees in one hole

[I enjoyed Jeff’s Valentine story so much that I thought I’d stick to the theme of togetherness…for better or worse.]

A week or so ago a reader asked about the practice of planting three or four fruit trees in the same hole.  Having not heard of this before, I checked on the web and found many “how to” pages geared to home gardeners who either want a longer harvest of a particular fruit (early to late) or a mixture of different species.  Doesn’t it sound just great, especially for smaller urban yards?

One of these sites has these written instructions: “Plant each grouping of 3 or 4 trees in one hole at least 12 to 15 inches apart.”

Now, I’m sorry, but this is just asking for trouble down the road.  Readers of this blog know that root systems extend far past the drip line, and that roots from different trees are going to compete with one another.  You’ll end up with three unhappy trees, all jostling for space and resources, just like kids in the back seat during those long car rides.

But wait! you might say.  There’s research on high density tree planting, and it’s been shown to increase fruit yield on a per acre basis!

Yes, in fact there is a lot of planting density research on many different species of fruit trees.  What’s considered by researchers to be “high density” varies, but it rarely exceeds 2698 trees/acre (6666/ha for our international readers).  Optimal and sustainable levels of high density planting are also variable, as they depend on not only species but rootstock and the crown architecture; 1214/acre (3000/ha) might be a mid-range number.  This can be converted to a per-tree requirement of 36 sq. ft. or a 6’x6’ planting area.

How does this compare to the 12-15” recommendation given earlier?  If we’re generous and use the 15” recommendation, this translates to 6.25 sq. ft. per tree or 6970 trees/acre.  The 12” recommendation would lead to a whopping equivalent of 10,890 trees/acre.  (And no, it doesn’t matter if you’re using dwarfing rootstock or not; most of the higher densities in the literature are for dwarfing rootstocks.)

You don’t have to be a math whiz to see that these densities are totally out of line with reality.  Sure, you can probably keep overcrowded trees alive with lots of water and fertilizer, but they’ll be under enough chronic stress so that pests and disease might take hold, and fruit production will likely be poor.  And it’s about as far from a sustainable practice as you can get.

More Master Gardener Fun!

Am just heading out the door for Fairfax, Virginia – part of the greater Northern Virginia metro area, with traffic that scares the pants off of us country mice. I’m doing the Master Gardener training for the Fairfax Master Gardener Association.  Their attendance is so huge, they have to split into a morning session (150 people) and an evening session (100+). Two and a half hours of training on “herbaceous plants” twice in one day – that’s a lot of yakking even for yours truly.   But what a terrific group. I led the herbaceous sessions in 2007 and was impressed at the diversity of age, ethnicity, levels of knowledge, you name it. A complete cross-section of the area, all with the common desire to learn. Merrifield Garden Center generously (and brilliantly) hosts the training in their large meeting room. Alas, after we all get worked up over the fab perennials, annuals, and tropicals, there’s not much to buy this time of year.
I’ve written about the tremendous contribution of volunteer hours that Master Gardeners make to our state.  As the budget axe drops hither and thither, Extension programs always seem to be at risk. All of the Garden Professors have noted their own state’s struggles with such. Here’s the (slightly) brighter side, though – the Fairfax Master Gardener Association receives no funding from federal, state, or local government. Just some training materials from Extension Same with most of the other associations across the state. Not much to cut, really. In turn, it was calculated that MG volunteers across the state reported 334,000 hours of service for 2009. That’s a pretty good return on very little investment from the state.  Heck, I don’t even have an Extension appointment. But I’m a believer in the MG system, and want to help in whatever way I can, even if it means leaving the peaceful mountains and driving to Northern Virginia. A bit of a bonus is there’s really good shopping up there. Heh.