Thanks for writing. Perennials almost always take longer to become established when you plant them beneath a big tree because the tree's root system absorbs so much moisture and nutrients from the soil.
You can help your plants along by giving them some fertilizer and extra moisture during the spring and summer growing season.
You don't want to build up the soil --- adding too much soil could start to suffocate the roots and wound or even kill your tree.
---Justin, Senior Garden Editor, BHG.com "