Little Joe Dwarf Pye Weed 'Eupatorium purpureum' is a perennial that is great for small areas with moist soil.  It's size is about 4 feet tall and can spread to about 30-35 inches so it doesn't need a lot of room and will grow fast.  The plant is covered with dark green leaves and in the mid-summer bloom fragrant mauve flowers.  It would be great planted behind other perennials or ornamental grasses. 

If you like butterflies like monarchs and swallowtails, they are attracted to this perennial plant which will come back year after year.  It is also deer resistant, is adaptable from full to partial sun and hardy from zones 3 to 8.  In the winter the wine red stems will also add a lot of color at a typically less colorful time of year.

I think planting it next to a pond would work well and with the water attraction and sunlight should attract a lot of butterflies and since birds are attracted to water, you may even find a Hummingbird or two.  These plants also have fluffy seed heads that the birds collect for nesting materials. In addition to enjoying the plants, I find watching butterflies and birds very enjoyable and relaxing, maybe you will too.
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