First, that weird name, Lead Plant. Says the Missouri Botanic Garden, the plant was once thought an indicator of lead in the soil. Meaning what? Lead to mine? Or lead contamination, land to avoid? Doesn't say, dunno. As usual, Latin is better. Amorpha canescens. Amorpha means mis-shaped, in that the flowers are missing most of the petals their other pea-family relatives have. Just one here, thank you. Canescens means grey or hairy, which the delicate ferny foliage certainly is.
The plant is as tough it is adaptable, native from the Canadian sub-Arctic to the Gulf Coast. At home, it's a small-scale early-Summer thrill to puzzle experts as well as just-folks gardeners.
The profuse spikes of indigo-blue flowers are way too early to be caryopteris, which is the same size bush (a foot or two high and two or three feet wide) but doesn't bloom until August. But caryopteris foliage is simpler and a bit bigger anyway. As are the leaves of buddleia, the other possible floral look-alike. But it too is in bloom much later in the season, not by the end of June, and even in the dwarf forms is distinctly bigger and more erect.
All Lead Plant wants is these three things:
1. Lots of sun.
2. Good drainage in the Winter. 3. Freedom from herbivores, deer included: The foliage tastes great (to them) and is nutritious too. No idea of its lead content though. And all you need to do for your Lead Plant is to cut it to the ground without mercy in early Spring: As with caryopteris and buddleia, the flowers happen at the tips of new growth, so last year's isn't worth a damn.

I haven't been face-to-face with actual marijuana for, oh, 40 years. Tried it, didn't like it. So I was very slow on the draw in realizing that one of my vitex bushes is doing a serious pot imitation.
Here's the bush, putting out its lush eager Spring growth.
A foliage close-up. Look familiar?
And here's a shot of an actual marijuana. (Thank you, Google.)

They are amazingly similar, but pot has more leaflets than vitex. Seven instead of five. And pot leaves are two or three times as big.
But with pot, as with vitex, the puff I mean the proof is in the pudding. When the vitex blooms it gets narrow spikes of tiny lavender-blue flowers, not the odiferous buff-colored clumpy things of marijuana. OK, blue-ish with today's pot-imitating species, Vitex incisa. Perhaps this is the reason that if you only have one vitex, plant what everyone else plants, Vitex heterophylla. Here's one of those in bloom out in Wellfleet. Now that's colorful!
But you know me: If I have one of something, well why not have all of its cousins? So I grow Vitex incisa too. That's one of my, ahem, hardy passion vines, 'Incense', crawling through the vitex, and adding one of its flowers to the picture.
'Incense' is far and away the easiest of the passifloras to establish, and the flowers are are the biggest too.
Incredible. Sun in the Summer, good drainage in the Winter, and you should be able to get some 'Incense' in your garden almost anywhere in Zone 6.
A nice druggy coincidence there. The name if this variety, planted so near my inadvertently pot-like Vitex, really is 'Incense'. Just as incense tried to do with pot in real life (I'm told), this 'Incense' is trying to cover up this "pot." Even better: 'Incense' was developed by the US Government, who was trying to create a hardy passion vine with an agricultural fruit crop. But instead—you can just hear those dweeby DOA guys saying "darn!—all they got was a hardy passion vine with incredible four-inch blue flowers. That still doesn't explain why they named it 'Incense', though. Maybe they were smoking something that day? A thought.

Butterfly bushes usually bloom in Summer, at the tips of the new stems they started that Spring. So last year's growth isn't useful at all: After growth starts in the Spring, cut each limb back to the lowest possible pair of new leaves. If you're not horrified over how drastically you've pruned, keep going.
There's a butterfly bush that blooms in Spring too, and so whatever you do for your Summer-blooming butterflies, do the reverse for this one.
It blooms on last year's wood, so don't do any pruning until the bloom is well underway, or even finished. And while Summer butterflies often get huge amounts of Winter die-back, Spring butterflies are so hardy that their wood lives year after year, and they can get bigger and bigger: As big as a lilac, and usually much wider.
But since my philosophy is "Why let anything grow naturally if I could be torturing it instead?", I'm getting out the pruners to take full advantage of my Spring butterfly's oddball talents.
The wood is hardy year-to-year? Fine: Then I'll pick one main branch, stake it up, cut off the lower limbs, and—voila—I've got a small tree, a "standard" as we say.  A "standard" as anything that's trained into a ball-on-a-stick form that wouldn't otherwise grow that way.
The younger branches tend to weep, especially as they bloom? Great! I'll get the trunk high enough so that I can have a (small) weeping tree.
And the bush comes in a form with conspicuously silver leaves, not just the regular fuzzy green ones? That's the one for me.
Here's the progress, then, on my silver-leaved, weeping, standard of Spring-blooming butterfly bush.
I've staked up a center branch to grow as a trunk, but then, in the way of much in any garden, got involved with a million other things for a couple of years. Time to prune and primp and reveal what's what.
How 'bout those lavender blooms in three-foot-long spikes? Every garden needs more fireworks.
With the stray lower branches pruned off, the young standard's trunk and head-growth are showing nicely.
And as the plant ages, the number of branches in the canopy increases nicely, making a fuller, wider, and lower-weeping canopy. That's a deep-purple ninebark bush at the left-front, cut to the ground each Spring. It will get six feet tall by September, which is just how tall I should get the butterfly's trunk so the weeping silver branches will mix nicely with the purple of the ninebark.
That's a blue-leaved rose at the back, which will get big enough to form a darker background to the whole ensemble.
Give me three more years, and this will be stunning.
PS: OK, time to grow up and switch over to the Latin:
Silver-leaved Spring-blooming butterfly bush: Buddleia alternifolia 'Argentea'
Purple-leaved ninebark: Physocarpus opulifolius 'Seward'
Blue-leaved rose: Rosa glauca