Tree leaf out is part of a deciduous tree’s annual cycle. It is the production of leaves during the spring following winter dormancy. Leaf out is illustrated in this time-lapse video of beech buds and leaves opening, filmed by Neil Bromhall:
Each year the timing of tree leaf out differs. Many of you may be wondering why some of our trees, such as limes and oaks, are so slow to come into leaf this year and yet others, like hawthorn and maples are in full foliage. For many trees it is a game of risk. Those less able to withstand cold temperatures hold back their foliage in protective buds, avoiding putting energy into foliage which could be ruined by a late spring frost.
There are of course many factors that determine when leaf out occurs in different parts of the country, including soil and air temperature, day length, sunshine hours and rainfall levels. For example our native oak tends to respond well to consistent rising temperatures, whilst ash trees tend to respond to higher levels of daily sunshine to encourage leaf out.
The Woodland Trust hold a databank on budburst, flowering, and associated bird and insect activity which they compile each year. Check out data for 2020 which showed budburst was over 2 weeks earlier than the benchmark year for 11 tree species. We’ll be watching out for the 2021 data to see how this year compares.