Morning glort supports can be as thin as stiff baling wire and as thick as maybe an inch. I have no experience with the other plants.

Thanks!
Do you know how many seeds I would have to plant to get a nice bushy-looking plant? Could a shepherd's hook like the ones for hanging baskets on be a good support?

It depends on which species and variety you plan to grow to be able to answer this question. Which morning glory variety do you have? On the shepherd's hook, you might have a better presentation of flowers using the sweetpea vines. Try 3 seeds and see how it goes. Experience is the best teacher.

Thanks gerris2. Here are the vine varieties I have seeds of:

-Morning Glory "Heavenly Blue"; "Milky Way"; and "Old Glory Mix"
-Moonflower "Giant White"
-Sweet Pea "Burpee's Galaxy Mix"

I also want to buy some Black Eyed Susan Vine seeds.

Realize that the moonflower vine will grow into a massive vine. The sweet pea vines will be covered by it. I imagine the morning glory vines will grow through the moonflower vine, but the peas won't. The b.e.s. vine is also a small vine and will most likely not do well with the moonflower vine.

Sweet peas are insubstantial vines and I have never seen one row to 15 feet unless grown as a single stem cordon in very rich soil. Although the flowers are beautiful the vine itself is unimpressive. It climbs by tendrils so needs something thin to twine on. To keep the flowers coming you need to pick the flowers or dead head regularly. In the UK they are often grown in the vegetable garden for cut flowers because the plants are not much to look at. I grow three plants per stick or cane in a 5 - 6 cane wigwam. Even in our climate they are scruffy by late summer and in hotter places I believe they fizzle out even earlier.

Hi kayjones and floral_uk. Thanks for your replies!

kayjones- Do you know whether the moonflower vines would grow in a partial shade area? I have an arbor that gets good morning light but it is shaded later in the day. I will probably grow it without any other vines.

floral_uk- Would growing more than one packet of sweet pea seeds together grow a nicer display? I would hate to just have a few scraggly vines. Would planting more seeds together result in fewer blooms?

Can anyone answer my questions?

Hi again - clearly the more seeds you sow for sweet peas the more plants you'll get and the more flowers. You can grow them quite close together - a few inches for ordinary garden use. For show use they are treated much more carefully. Also you should pinch out the growing tips when they a few inches high to get several stems. otherwise they will usually just put up one single stem. I don't know where you live but here I would have sown them back in January indoors to get substantial plants to plant out.

Here is a link that might be useful: National Sweet Pea Society website.

Hi again floral_uk.
I live in zone 5 in the US. I have been reading up on sweet peas and I have read that they get pretty scraggly and don't bloom very long at all. But I'm guessing there are many factors that go into that, such as how much sun/water they are getting, what zone it is, etc...pretty much the same as with any plant. Growing vines is all new to me so I will consider this an experiment and hopefully I will learn a few things along the way.
I have been wondering if I should start the sweet peas indoors. I just started my Moonflowers and will also be starting morning glories indoors. Thanks very much for all of your help!

I would say the more seeds you plant the more vines and flowers bur I think you have to experiment. My dad had a b-e-s vine and it really took off and was blooming all the time. I think he planted a whole pack of seeds.

boncrow66,
I was thinking the same thing. Since this is the first year I'm planting vines, I will just take it as a learning experience.
My husband bought a big arbor for the front yard and I want it totally covered in flowery vines. It would look pretty pathetic with just a few scraggly-looking vines on it!
I hope the black eyed susan vines look as nice as they do in all the photos I've seen! I guess a lot of that depends on me, though!