cuckoo,
I think it would be impossible for any one to advise one way or another, as your specific environment is not likely to be common on many other properties. So I would suggest trying both direct sowing and starting seeds in doors. Take note for next year indicating which was more successful but don't plan on making any permanent changes until you have observed this experiment for at least three years. kt

I think runktrun offers good advice. Having said that, I'll also add that what I've read before (I can't personally attest to its truth) is that zinnias resent being transplanted.

I suspect there may be other annuals that will be more successful for you as direct seeded flowers. Both sunflowers and also zinnias are native to areas with warmer weather than Boston gets. You can certainly grow them, but don't be surprised if they don't really begin blooming until August, and then shut down not long after Labor Day. In the Philadelphia area you get much better results with both since they start blooming in July and don't really begin to fade until October.

For me, I have an open yard policy for most of my yard..meaning I have more squirrels than I can count on some days...I find them funny, intersting and great problem solvers..I get a kick out of watching them try to figure out how to get to my bird seed...silly creatures that they are..there's plenty on the ground for them....that's what lead to one problem with my direct sowing of seeds..my sunflower...they were the only one's they went after...I went and bought more and now are germinating them in the house...

I put out many other seeds, some winter sowing, some direct..they haven't been touched..just the sunflower..

You may not be so lucky however, maybe they leave my seeds alone because they have enough to choose from on the ground that I give them...

Good luck..I was pleased to read that you were not posting, "want to plant seed so need help getting rid of squirrels"..though I would and do completely understand people who do not share my feelings about the critters...

Thank you all for your replies. Squirrels are a bit of
a nuisance but I am trying to coexist with them... I
think I will start the sunflower indoors but will
experiment with other annual seeds by direct-sowing
(will keep some extra seeds on hand just in case).
They leave the established perennials alone so I think
they just can't resist the newly-dug up soft soil
around the new seedlings.

I think recently dug up areas automatically draw there attention. You'll find the same thing happening if you plant a whole slew of tulip, crocus, or hyacinth bulbs in the autumn. A day or two later the squirrels go specifically to the areas where you dug and investigate. Once they realize you've planted something edible and nutritious they dig them up and hoard them.

Plant daffodils and snowdrops. Those are poisonous so the squirrels leave them alone.

in the next couple of weeks, i'll take tops off 150ish sprouted jugs of winter-sown perennials and transfer those tops to cover new plantings.

for example, toward the front of my squirrel-infested yard, i'm doing a longish strip of sunflowers (red) & nasturtiums (climbing, soft yellow). i'll direct sow those & immediately cover each seed with a 2-liter bottle or milk jug top until the plants get to be about 3-4" tall & the soil around them has settled into something less intriguing to the wretched varmints.

i also cover just-seeded raised beds & bulb plantings with big pieces of wire mesh, sandwiched between bricks to keep the mesh a couple inches off the ground -- the plants get a fair headstart & the squirrels can't squeeze under.

i admit that the garden looks pretty ghetto until about the end of may/beginning of june, when new sprouts get big enough to fight off the squirrels & i can finally whisk away all the crappy plastic lids & wire clutter ... ta-dah! ... but a girl's gotta do what a girl's gotta do. i live alone at the end of a dead-end street and, honestly, my neighbors can bite me. i will lavish them (the neighbors, not the squirrels) with tomatoes at a later date as penance for having an oddball yard.

best of luck!

:0)

Here is a link that might be useful: {{gwi:1067091}}

Thanks for additional tips. I actually already have
snowdrops and daffodils planted, and the squirrels
certainly don't touch those! They haven't bothered
with muscari and species crocus either.
The milk jug and wire mesh approcahes sound good--
I might try that in the back yard flower bed.