One of the joys of working on a university campus is that construction never seems to end. As near as I can tell there are about 3,000 orange construction barrels that permanently reside on the MSU campus that simply get shuffled from one end of campus to the other every few months. Along with all the construction comes a never ending series of new landscape projects. Driving by one of the most recent projects the other day got me to thinking about the myth of Fall planting. In numerous extension bulletins and certainly in nursery sales advertising we hear that “fall is the perfect time to plant trees”.
Photo: Dana Ellison
The recent fall planting job on our campus gave me pause to think about this. I haven’t had a chance to completely survey the carnage but I suspect about a third of the trees will need to be replaced. Obviously there are lots of things that may have gone wrong here, irrespective of when the trees were planted and one exception doesn’t prove the rule. Nevertheless when I look back on the planting disasters I’ve been called in to inspect over the years a disproportional share (I’d say by a factor of two or three to one) are fall planting jobs.
What gives? Well, the notion that fall is a great time for planting is built in a faulty premise, at least for this part of the country. Probably the most commonly cited reason for fall planting is that trees grow a lot of roots in the fall. This assumes that since there’s no shoot growth occurring, trees automatically shift reserves below-ground. There is certainly a ‘pecking order’ of carbohydrate distribution within a tree based on relatively strengths of sources and sinks. But there’s one factor that trumps all others: temperature. Soil temperature is the biggest driver of root growth. Measurements of new root growth in a cottonwood plantation in Wisconsin provide a classic example. As temperatures decline in the fall, new root growth essentially ceases. For trees that are well established, this is no problem. For trees that have just been transplanted and need to re-establish root-soil contact this is a tough row to hoe. Throw in a tough Michigan or Wisconsin winter and the tree’s facing an uphill climb.
New root growth of eastern cottonwood (top) and soil temperature (bottom). Source: Kern et al. 2004. Tree Phys. 24:651-660.
Again, most planting failures have multiple causal factors. Even if the trees on this site had been planted in the spring, they may have still experienced problems. My point is that a more accurate statement is “Fall is an OK time to plant trees”; not the ‘best’ time or even a ‘great’ time. I think these statements are often driven by the fact the fall is a slow time for nurseries and landscapers. When homeowners or landscapers ask me about fall planting the first thing I ask is if there is any reason why they can’t wait until spring, the real ‘best’ time for planting.