Glassonion91168 wrote:
Moonflowers
Morning Glories
Zinnias
Coleus
Sunflowers
Marigolds
Tomatoes (endless summer and plum)
Maybe watermelon
It does make a difference what it is. Of your list I would start indoors: moonflower, coleus, marigolds, tomatoes. I would direct sow in the ground morning glory, zinnia, sunflower, watermelon.
For me part of the deciding is how quick they are to germinate and then to grow. The longer it takes the seed to germinate, the more bad stuff can happen while it is sitting in the ground waiting- too much rain waterlogging it, too little rain drying it out, etc. It is easier to provide the constant good conditions indoors. The moonflowers are difficult to germinate, need to be scarified and then soaked and kept moist. The tomatoes take 4 months from seed to ripe tomatoes. If you don't give them a head start indoors, you won't have a very long productive season before fall frost ends them. Marigolds are a bit slow sprouting and growing for me and I like to have them ready in bloom to pop in when I am planting the other stuff.
Things like the zinnia, sunflower, watermelon, if you just wait until the soil is well warmed up, they sprout and grow very quickly and don't really need the head start.