Flower gardens are very personal and for this reason I reluctantly suggest plants. I suggest you contact your local Master Gardeners organization through the Ohio State Cooperative Extension Service for info specific to your area.
Good luck and happy gardening.

Young seedlings need quite a bit of light. Sometimes the light from a window sill is not enough. If your seedlings get too tall and stringy from stretching for the sun, they will never do well. What you are aiming for in a seedling is short and fat. Plants with enough light do not get what gardeners call 'leggy' from desperately trying to reach the light. That's the most common mistake new gardeners make. They think that a tall seedling is a good thing. It isn't. If your days are sunny, after your petunias are all up, you can take them outdoors for a few hours in the sun. Don't forget them overnight and chill them.

Petunias, marigolds, lobelia, allysum, geraniums, of course, all do well in pots---as do a ton of other flowers and vegetables. You can always ask at your local greenhouse, too. Do you have a certain color scheme you're hoping to achieve? Not all flowers come in all colors, so that may dictate your choices.

If you notice a flower you like in a neighbor's garden this summer, ask them what it is. Write down the date you saw it in bloom in their yard. Gardening journals are very helpful to consult from year to year. What worked. What didn't. What you loved. What you hated.

Zinnias are easy directly in the ground. The above mentioned plants do well in the ground, too. Again, you have a lot to choose from. I'm mentioning plants that new gardeners usually find easy to grow from seed.

Good luck!

HI! I am originally from Ohio with some experience gardening there! The first thing I would say is be patient. I know it is hard when you are excited about your first plants! For Ohio, I would wait until around Memorial Day to place plants outside. I had most success that way. Also, don't worry about the morning glories. They will take off like weeds this summer after planting. I usually planted the seeds directly in the ground, and, once again, had to be patient! Also, don't water your petunias too often in your pots while you are waiting. Just water when you notice that the soil has just dried up. A mist is nice for the foliage each day. Hope this helped! Give us an update!

About the Petunias in the six inch pot: if you intend to move them on to a larger pot as they settle in - no problem. Several in a six inch pot will be pretty hard to separate once they develop their roots and leaves. They'll have a set-back to their growing when you do it.

If you want to plant them out later to make a row of separate plants it is probably better to plant each individual plant into its own two inch wide starter pot. Use a mix that is quite gritty - preferably with NO peat. You can keep them on the windowsill and give them a half turn each day as if you were spit roasting. That way they get to grow up straighter.

While they are in the starter pots, unless you need to check the colour - don't let the buds develop. Snip them off with your Best Thumbnail (your own physical thumbnail) - or a pair of florist's snips. That way the growth is going into the leaves and roots for now. Flowers later.

Keep an eye on the bottom of the pots (which will have plenty of drainage holes). When you see white thready roots coming out just a little way either - put the plants into the next size of pot, that leaves at least half an inch all round the ball of roots; or plant out into the garden.

Before you plant out - dig over the area you have in mind to at least twelve inches down, and add in plenty of ancient compost, (so old you could never tell what went into it) and, if it fits with your thinking, either steer manure pellets, or a general garden fertiliser - about a handful to the square yard. You can do this weeks before you are ready to plant out.

Stuff in pots: go for bigger pots rather than zillions of littles. There's far less work involved and the size helps to keep the moisture better. If you have very dry summers - add water crystals to the mix. Despite the wonderful pots shown on YouTube and the garden shops - it's probably better to plant fewer plants into the pots and make up for it by good feeding and watering over the growing season.

In hot and windy weather you may need to water twice a day. If your schedule doesn't let you do this, forget about the big pot and basket displays. Gardening is supposed to be enjoyable and relaxing, not anxiety and fret... The plants will do better in the ground if you give them the sort of attention you'd lavish on them in pots.

Unless the weather says otherwise, your Petunias will last and flower for more than six months so they'll be there through your early summer, full summer, and autumn displays. Sort of like the living room carpet that you match your drapes and upholstery to.

If you are keen on pots - use them for accent plants that you can bring out for summer and tuck away in the basement or garage to stay safe over winter. More tender things such as banana plants, or canna, or dahlia. For the shady areas - really nice ferns and Hostas and New Guinea or 'ordinary' Impatiens. They can make a cool place quite lush and exotic. Lovely for...