Our Davidia has grown from 1 metre to 5 metres in about 7 years. Last year we had a prolific show of hundreds of handkerchiefs; this year just three! Two years ago we had hundreds of large (2cm dia) seed pods with just 3 handkerchiefs. Can we expect handkerchiefs to show every other year? The tree is in middle of large lawn, enjoys every aspect and has no competition from surrounding trees. We feed it every spring. Please advise.