I would certainly encourage what people have said about deepening the border. If this is your main perennial or mixed border, it is very hard to get excited about and get experience with plants without a significantly deeper border. 6' is probably a minimum in my book, with give you barely enough space for three "rows" of plants (though generally we don't plant in rows...). If you have the courage to delve in, there is nothing wrong with making the border even deeper in some sections. Putting in a small stepping stone path can help with maintenance access where the border gets deep and give it some interest in the winter. A couple of well chosen shrub and clematis will give you a lot more height variation and seasonal interest. Choose from smaller viburnums, elders, mockoranges, roses -- any number of plants. And Clematis on obelisks will weave and knit over adjacent large perennials and shrubs. Others may disagree, but in a cold N temperate climate, I personally don't care for most dwarf conifers planted in a bed mainly devoted to perennials. They are very stiff and static looking. And to me they end up looking very lonely in the winter, don't add much. In a crowded overflowing border with no bare soil (my kind of planting), many conifers will not grow that well and may have too much needle damage from crowding by perennials. Personally, I think deciduous shrubs with multiple seasons of interest are better choices, tolerate crowding better, often grow faster, can be used as clematis scaffolding, and in my hands are just more satisfactory. You won't be able to get more than one or two but they will add a lot. Another thing to do will be to add big, shrubby perennials -- ornamental grasses, persicaria polymorpha, etc.

Thanks for the reply. It's a very large mature mixed border and there's not a lot of space left for new perennials. It's also on a fairly steep slope so I have to be careful to plant things that don't typically flop. I learned through trial and error over the years what grows well with minimal maintenance and looks good throughout the growing season. There is already some early season color from knockout roses, heuchera, variegated iris amd May Night salvia and some sprirea. I use some self seeding annuals, particularly cosmos, to carry color through most of the growing season. I,m looking ahead to a graduation party I'll be hosting in early June next year and had the idea that there may be some earlier blooming annuals that can be sown from seed this fall to add a splash of color at that time.

i agree with you, sue. i have been playing more with tropicals, but mostly set off on their own. for some reason, for instance, i find that in my own gardens, i'm not comfortable trying to combine flowering tropicals with non-tropical flowering plants.Ex. Cannas: i have them in their very own wet bed, with some strong colored though non-tropical foliage. i like the black leaved cannas, so i have them in w/ yellow acorus edging backed w/ ligularia marie... and vitex agnus castus and varieg bamboo and black colocasia.and ravenna grass. in trying to figure out, right now,why i feel this way about cannas, i think it must be their loud flower colors- which don't go well in my borders. and i guess when i see them, my mind strongly subconsciously feels that if i'm not in calif or hawaii, they don't belong. ha. oh well...i do love them as the alpha plant in their own bed. best, mindy

If the heavy soil is killing the flowers buy lighter soil and dump it on top, without mixing it with the existing soil, plant in that. Or choose adapted flowers. You will have to do the same with shrubs, if the kinds you want don't like clay soils they won't be any happier with the existing soil than the flowers were. Is there a hedge, wall or solid fence behind the border, as in the above photo? If not you should install such or plant evergreen shrubs behind, informally arranged, as well as at corners or ends to in either case form a sort of stage for the smaller plants (groundcovers and dwarf shrubs, if no herbaceous plants are to be used). In the well-designed mixed border deciduous shrubs serve primarily to form transitions between the bulkiness of evergreen kinds and the lightness of non-woody plants. Flowering climbers like clematis and roses can be trained on fences, walls or hedges, to include them in the planting, as well as large deciduous shrubs like lilacs that provide no summer interest otherwise.