I recently panicked and cut and pulled off some brown pine-like cones appearing on some of my Green Giant arborvitaes. I have since learned from your Web site and various others that these brown cones are a normal fertilizing process of the female tree, and these seeds are needed. Does this mean I have done some damage to the trees, and should I keep the cones and spread them around the trees so that they can help serve as fertilize in the spring?
The Gardener’s Answer
Hi, Alexander in Maryland: Arborvitae ‘Green Giant’ (Thuja plicata) does produce small pine cones that are much smaller than the pine cones we typically see on other conifers. The purpose of the pine cones is reproduction. It is basically a shelter for seeds to live in until they are mature and ready to be released and planted. After this evergreen flowers, it produces separate male and female cones on the same tree, which technically are considered fruit. The male cones are round and found at the ends of the foliage while the female cones are still small but a bit more elongated in shape and a bit larger than the male at maturity. While they are green during the summer months, as they mature, they turn brown. There is no reason to remove the pine cones in the future but you have not jeopardized the health of your tree by doing so this year. You could not have possibly removed all of them and pine cone production in general differs every year depending on moisture, temperature, and other environmental factors. You certainly can leave the cones around the base of the tree but it will not benefit the tree in terms of nutrients.