We think of summer as the “growing season” and we are used to our garden plants growing all summer. For most trees, though, growth takes place mostly in the early spring. Most trees in temperate regions produce a single flush of growth – the bud opens, and leaves that were formed the previous year expand to their full size, and growth stops. Shoot growth is often finished for the year by June, even earlier in some trees. In a typical year, a new bud will form and rest until the following spring. (Some trees have a different pattern of continuous growth – more about that later).
In some years, trees can be stimulated to think that it is spring again, and to start growing. That is happening right now in Kentucky. After a very dry spell, we have had a lot of rain. This has stimulated a lot of trees to grow again. If you look around in the next few weeks, you will see what is shown in the first picture – a flush of tender, new leaves above the earlier spring leaves.
Occasionally, conditions will be perfect for multiple flushes. Last year (2013) was such a year. From early spring until fall, we had short dry spells followed by abundant rain. In the lower figure, each year of shoot growth is marked. 2012 was a pretty good year (blue arrow) for a single flush of growth, while there was less growth in 2009=2011. Then came 2013 with growth starting and stopping three times. Each time, the tree (this is a swamp white oak) produced a flush, set a bud and then, after a few days’ rest, began growing again. As a result, there was enormous growth in 2013. We may be seeing the same growth this year.