I know that my cedar is at least 100 because my neighbor had his cut down and sold and we were offered $ for this one and told the est. age. Anyway, I'd like to know if I can plant anything underneath. I have perriwinkle(only grows to 1 side for past 3 yrs.and stays small) I planted 2 lilacs and forsythia nearby, but not growing much (3rd yr. this spring) They get sun. Is the cedar sucking everything up? Should I add something to soil? Lilacs&fors. are @5ft. away fr. tree.
A cedar that big is probably taking much of the available summer moisture, which is why many plants don't thrive under them. The root system of the cedar will extend quite a bit wider than the widest branches on the tree. You can mulch and provide supplemental water to the shrubs you have planted, but you might consider planting more drought tolerant plants there, perhaps choosing natives. I would still expect it to take 3-5 years of deep, infrequent summer watering to establish what you plant. Also, lilacs need neutral to alkaline soil to bloom well, and the site you've chosen likely has acidic conditions. I have found that my lilacs do best in full sun, away from other trees, with annual lime applications.
