when discussing 'shade' its nearly impossible to come to many conclusions.. but for trying things in whatever your sun actually is . just go for it ...

short of a dark grotto .... plants usually do not die due to lack of sun .... speaking of only one variable for now [dark shade is usually associated with heavy trees.. which also adds water competition issues.. etc] ...

how they respond is by etoiliating.. stretching to the light ... lack of vigor.. reduced flowering etc .... and once you see that.. you would decide to move a perennial to a better location .. but in the mean time.. you are growing out a plant.. so its not a total loss ...

also ... many trees are deciduous ... and spring sun is much more efficient for young or newly planted plants ... so by the time the shade peaks.. the plants can already be to a size sufficient to deal with it all ...

having been a hosta maven.. with glasses that darken ... i can tell you i have been in 'shade gardens' so dark.. i could not see thru my glasses... and it was rather useless to take off my glasses to 'look' ... lol .. and i have been in shade gardens so bright.. i had to squint thru the darkened glasses ...

so when dealing with how something will grow in your specific 'shade' .. all you seem to be left with is ... WING IT ..

its good to ponder all the variables ... but i am one who experiments.. with placement ... rather than 'worry' about it .... you will live with my decisions you mangy plant.. or i will destroy you ... but i will move you once ... before i sacrifice you to the compost gods ... lifes too short to deal with your foo foo attitude ... but i digress .. lol ...

ken

I think I am seeing some candidates for my best quotes of 2018 thread...

Ken I do appreciate your mantra to experiment, experiment, experiment. I have taken it to heart. HOWEVER, I am still interested in the science of plants' use of sun. They etiolate to reach it, but once they do, will they fill out and flower fully? Or does an etoliated plant remain stunted forever? Who is our scientist here - Babs?? Now on a personal level, I beg you to indulge my less experimental mood this year. I am planning two garden weddings - June 2 and August 4! Anyone who's seen how many questions I post here can imagine how far I have to go! I suppose i could put up signs here and there explaining the experiments and their apparent results..laminated, of course, in case of rain. (Reading from my garden diary for the last June 2's---- "deluge flattened all siberian iris and peonies.." etc.

Have you thought about growing them in containers until they are tall enough to clear the hydrangeas? Would be extra time to keep them watered, etc, but they'd get full sun for a large part of the growing season. you could even place the pots in the bed where they will be put on top of some kind of riser (like an upturned pot underneath) to keep them out of the way/off the yard and elevated to get full sun.

I only direct seed when I have a lot of seed and I don't much care exactly where they end up growing because the competition from other plants can prevent them from sprouting if conditions aren't to their liking. I agree with the suggestion to start in containers, especially since you really want the garden to look good and have a specific spot where you want them. Plant in the garden when sized up. There can be issues with direct seeding, including that seed sprout best when they are happy, and it's easier to provide ideal conditions in containers; it is easier to figure out which are wanted seedlings in a pot, whereas garden soil has lots of weed seeds to add confusion; you can get them started a bit earlier since a warming mat can give you warm soil sooner.

Look at white cosmos which in my garden has been vigorous, long-blooming, and easy.

Timing of blooms for something like a wedding is really tough unless you have really long bloomers, so have a backup plan such as having pots available for moving in to fill bare spots and places where critters or weather have damaged plants.

Are the plants surrounding super high already? If not, many perennials die down to the ground in winter and then grow back up on the Spring. Spring is the perfect time to slip in a few youngsters when the older ones are growing out.

If we give enough room between plants for full sized growth, then the sun is up in the sky with several hours around noon almost directly overhead. I believe that the young plants should have sufficient sunlight in a "full sun" location.

Next item - prettying up the garden for a party. There is no shame in my book going out and plopping a few annuals here and there from the local big box or nursery. Even a few of those baskets ready made from your big box store spaced in front of the garden for more color and coherence are totally fine IMO. The reason I say this is many perennials don't fill out until year three or so. However, annuals mostly bloom their short lives off not being concerned about saving energy for next year or establishing a huge root system first.

I do this in my yard but I either start with home grown plugs(tall zinnias) or purchased small plants. I don’t direct sow. Key is there needs to be a gap between the plants for the seedling to grow through. Doesn’t have to be that big. If the canopy of the existing plants closes over it I would not count it pushing through.