Rainy September sets up colorful autumn leaves display in Delaware Valley

PHILADELPHIA – Turns out rain in September is really good for fall color in October, as a wet late September sets us up for more leaves on the trees in October.

“When there’s water present in the soil, the tree will hold onto leaves a little bit longer,” says Ryan Reed, a scientist for the Pennsylvania Department of Conservation and Natural Resources Bureau of Forestry.

If the soil was consistently on the drier side or if we had a late summer drought, trees would hold onto their leaves for a shorter period of time.

Strong droughts can even the delay the transition to fall color on leaves, according to the U.S. Forest Service.

As for this year, the stretch of warm, sunny days with mild nights starting the first week of October puts us in good shape to see vibrant colors later in the month.

The U.S. Forest Service says on warm autumn days like we’ll have next week, leaves will make lots of sugar. With mild nights, the veins you see on the underside of a leaf will gradually close, which helps keep the sugars in place. The combination of lots of sugar production and slowly closing veins leads to more red and purple leaves than usual.