1. Use a good shovel or even knife to cut down into the ground near the plant. You will be cutting some roots but it shouldn't be enough roots to give negative impact on the remaining plants. Take the other plant that you are trying to move to another spot.

In the future, you'll probably have to do something like this for some of your perennials, so you can get used to cutting through the ground or mound of a plant and know that you're helping the plant more than hurting it if you divide it or make it less crowded.

2. For other parts that are not being covered by some desired plant growth, you can use mulch. You also should consider mulching under plant stems that are bending over, even if they are blocking out weeds for now.

3. Lay out your compost in a thin layer several times a year. It shouldn't be eventually building up and increasing your ground level. If you add mulch, you will probably want to move the mulch aside when you add compost.

If the plant is not growing yet, you may not need to side dress that particular area. I mention this since I assume you are focusing the compost on the current plants, not trying to add compost to the entire garden area every time you add compost.

Alternatively, you can use your compost by making compost tea and feeding the plants that way.

Thanks, gp.

I will adopt your "little and often" approach for the compost- hopefully a very thin layer means it doesn't matter if some of it gets on a peony crown or whatever. My aims are to slowly improve the soil and feed the plants, so I want organic matter added whenever I can, but I don't want to dig it in and disturb anything already there.

As for the overcrowding, certain parts are looking a bit better since I ripped out all the post-flowering forget-me-nots. I'm leaving the cranesbill until the autumn because the bees LOVE it, but I'll definitely split those. Will also need to move some irises and a rose. Oooh...poor rose has already been moved once!