Frillylily,
I care for a Hosta garden in a local display garden that is situated underneath 4 large Hemlocks. This year it has done very well, but before I cared for it, it was a mess. Two things seemed to make a difference, lots of water and fertilizer.
The Hemlock roots are everywhere and the suck the moisture and nutrients out of the ground with alarming efficiency. I start with an early fertilizing of Milorganite (5-2-0) when the pips are just coming out of the ground. I throw it all over the bed like chicken feed. Don't skimp on it. It has the added benefit of repelling critters from eating the pips as well. Yes it smells.
This year I repaired the watering system for this garden and it has made all the difference. It's overhead sprinkling, and I water the entire area not just the Hostas. If you just water the Hostas and feed them, the Hemlock roots will go where the nutrients and moisture are and strangle your plants. Make sure you are feeding and watering the entire area so that the trees get what they need as well. I water this garden for about 2 hours a week with overhead sprinkling. Your garden may need more or less depending upon your soil's ability to hold water and the volume or your watering system. You just have to experiment with the amount of supplemental water you provide.
I do another fertilizing in mid-season, around the 4th of July. You can use an organic fert like Blood Meal or Milorganite again. Don't use a slow release. Use something that is available right away. I used some cheap 10-10-10 this year because that is what the display garden had available. It worked well.
This year I had to re-edge the garden two inches larger because the plants were growing into the lawn area. You can grow under Hemlocks, but it takes some care and effort. Below is a pic of the garden I care for.
Good Luck with your gardening.
Steve
