Is your perennial garden lacking in structure? Consider the spike. Sure, it might not be the most romantically named shape, but man, does it pack a visual punch. There are spikes for every season, but it's always seemed to me that spiky flowers are particularly present in early summer. Here are a few of my favorites.
Near the top of my list of plants I wouldn't garden without is baptisia (Baptisia australis and cultivars, zones 3 to 9). It sometimes goes by 'false indigo' because Native Americans used it to make a blue dye. Its blue spires point to the heavens this time of year, and it grows well in average to poor soil, in full sun to part shade, because it's in the pea family (which means it makes its own nitrogen), and has a taproot (which means it's best to plant it in one spot permanently).
Lots of exciting new colors are available now too. This one is called 'Twilite Prairieblues', and its flowers are purple, yellow at the base, while its foliage turns a steely blue that makes it gorgeous even when it's done blooming. At 3 to 4 feet high and wide, baptisias make handy stand-ins for shrubs during the growing season in lean sites that won't support shrubs.
Another of my favorites I haven't yet planted is the garden classic gas plant (Dictamnus albus, zones 3 to 8), so named because it supposedly gives off an oil that makes a tiny spark if ignited. It flowers pink to white in early summer and, like baptisia, would much prefer not to be moved once it's planted. Gas plant is an investment plant — it rarely looks great in pots at the nursery, and it'll take a year or two to grow to size in your garden, but it pays off once it does. Give it full sun to light shade and average soil. Gas plant grows to 3 feet tall and wide, takes moderate drought once it settles in, and requires careful handling, because the oils in its leaves and flowers can irritate skin.
The New York Botanical Garden
Mulleins (Verbascum species and cultivars, zones 5 to 8) are many and varied, but I think one in particular called 'Southern Charm' is a great garden plant. Unlike its many biennial kin (which flower their second year, set seed and die), it tends to come back every year. It's also more daintily sized, and its combo of peachy pink flowers with darker purple centers is to die for. 'Southern Charm' is happiest in full sun and lean, well-drained soil, and grows to around 3 feet tall and 2 feet wide. If you chop its flower stems off after it blooms, it'll often bloom again.
Acanthus, or bear's breeches (Acanthus species, zones 5 to 10) is another shrub-size plant that not only throws up amazing flowers early to midsummer, but its big, beefy foliage is a presence in the garden in it own right. Some, like spiny Acanthus spinosus, may be hardy into zone 5, while others like A. mollis (pictured) will do better in zones 7 (maybe 6b) and south. Plant it in full sun to part shade and average to lean soil – and take care planting in loose soils, where it may spread by runners. Most grow 3 to 4 feet wide, and up to 5 feet in bloom.
Finally, if it's a more casual spike you're after, there's always one of my favorites: 'Walker's Low' catmint (Nepeta x faassenii 'Walker's Low', zones 4 to 8). I mentioned it in our article on weed-smothering ground covers, it's blooming right now in my garden, and it's still one of my all-time favorites. Sweetly scented foliage and clear lavender flowers are trademarks, and it thrives in lean soil and sun. This "cat" grows to about 3 feet high and wide, and it's wise to give it that much space to spread out, because it may shade out other, less competitive plants.
Near the top of my list of plants I wouldn't garden without is baptisia (Baptisia australis and cultivars, zones 3 to 9). It sometimes goes by 'false indigo' because Native Americans used it to make a blue dye. Its blue spires point to the heavens this time of year, and it grows well in average to poor soil, in full sun to part shade, because it's in the pea family (which means it makes its own nitrogen), and has a taproot (which means it's best to plant it in one spot permanently). 
Another of my favorites I haven't yet planted is the garden classic gas plant (Dictamnus albus, zones 3 to 8), so named because it supposedly gives off an oil that makes a tiny spark if ignited. It flowers pink to white in early summer and, like baptisia, would much prefer not to be moved once it's planted. Gas plant is an investment plant — it rarely looks great in pots at the nursery, and it'll take a year or two to grow to size in your garden, but it pays off once it does. Give it full sun to light shade and average soil. Gas plant grows to 3 feet tall and wide, takes moderate drought once it settles in, and requires careful handling, because the oils in its leaves and flowers can irritate skin.
The New York Botanical Garden
Mulleins (Verbascum species and cultivars, zones 5 to 8) are many and varied, but I think one in particular called 'Southern Charm' is a great garden plant. Unlike its many biennial kin (which flower their second year, set seed and die), it tends to come back every year. It's also more daintily sized, and its combo of peachy pink flowers with darker purple centers is to die for. 'Southern Charm' is happiest in full sun and lean, well-drained soil, and grows to around 3 feet tall and 2 feet wide. If you chop its flower stems off after it blooms, it'll often bloom again.
Acanthus, or bear's breeches (Acanthus species, zones 5 to 10) is another shrub-size plant that not only throws up amazing flowers early to midsummer, but its big, beefy foliage is a presence in the garden in it own right. Some, like spiny Acanthus spinosus, may be hardy into zone 5, while others like A. mollis (pictured) will do better in zones 7 (maybe 6b) and south. Plant it in full sun to part shade and average to lean soil – and take care planting in loose soils, where it may spread by runners. Most grow 3 to 4 feet wide, and up to 5 feet in bloom.
Finally, if it's a more casual spike you're after, there's always one of my favorites: 'Walker's Low' catmint (Nepeta x faassenii 'Walker's Low', zones 4 to 8). I mentioned it in our article on weed-smothering ground covers, it's blooming right now in my garden, and it's still one of my all-time favorites. Sweetly scented foliage and clear lavender flowers are trademarks, and it thrives in lean soil and sun. This "cat" grows to about 3 feet high and wide, and it's wise to give it that much space to spread out, because it may shade out other, less competitive plants.