First time growing petunias,nasturtiums and marigolds
 

This is the first time growing these.Marigolds are 2 inches high with 2 and 3 sets of leaves.Nasturtiums are around 4 inches tall and petunias are still small.The weather is going to be in the 50's and 60's later this week during the day.Right now I have them under my shop lights but I need the space for my tomato and some pepper plants I need to repot into larger cups.At what temperature can they go outside?I have a couple 20gal aquariums not being used I could use as a greenhouse.I could bring them inside my garage when the sun sets for warmth.Any tips will be appreciated.I hope to repot my tomato and pepper seedlings next week.:)

I haven't grown petunias, but nasturtiums and marigolds are both pretty tough. If you aren't getting frost you could leave them in a sheltered area. If there is still frost the aquarium idea sounds great, as long as the full sun on it doesn't get too hot.

It's still frosting at night but I can get them in the garage.I have a lid on the tank that I can open to vent out the heat.This will help in harding them off.:)I'm still a month away from planting outdoors.Petunias go in a planter and some in the ground.Nasturtiums and Marigolds around my garden in the ground.

I know more about the nasturtiums and marigolds, not petunias, so I am addressing those two plants.

Definitely don't plant them in the ground until the soil has warmed, but I think that you can repot, harden off, and then leave outside on warmer days and even on warm nights.

I agree with Hatgirl that nasturtiums and marigolds are pretty tough, but I think that nasturtiums are the tougher of the two during cooler weather.

I also agree with Hatgirl that the aquarium is a good idea but you also have to be careful that the plants don't get too hot.

It sound like you are prepared to be schlepping the plants around to accommodate the weather, so another option is to put them in portable planters, if you have planters that you can move around, transplant, harden them off and then keep them outside, and only bring them in on cooler nights and days.

The nasturtiums will probably respond well to being potted up, and will probably start blooming for you in a few weeks.

I grew all 3 last year but direct sowed the nasturtiums outside at start of May. I didn't have space for all the Nasturtiums and Marigolds in cells. I set them out during the day as long as temps were above 40. I brought them in at night and put back under lights until bedtime. I planted outside at start of May last year here in Pennsylvania. Good thing you got a jump on the Petunias. They were very slow germinators and took awhile to get growing. Good luck!

I planted my nasturtiums yesterday, they desperately needed it. I think they will be okay, it's quite cool and rainy today but the rest of the week is supposed to be nice and by end of week near 80! I have been hardening off for a month. Nasturtiums can tolerate "cool" weather much better than the extreme heat of the summer. I will plant my marigolds and zinnias in a few days.

I planted both marigolds and nasturtiums right at the date of last frost (around 3/1) and they are thriving. Long vines on the nasturtiums are starting to put off flowers. I haven't let the marigolds flower yet, I've pinched them back to make them more bushy buy they're fine. We hit 40 degrees over the weekend and they are all fine. They'll grow slower in the cold but they can take it.

I’ve never had luck transplanting nasturtiums. They are cooler weather,related to radishes so I’ve planted direct sown at about the same time as I plant cooler weather stuff.’marigolds are so easy,just toss the seeds where you want them when you plant tomatoes.
I’ve not ever grown petunias from seed. They like temperatures similar to tomatoes,hot weather but not as hot as summer in Arizona. My mom actually grows petunias in the winter in Phoenix but most places it’s a summer flower.

My first time with all three from seed,I have more marigold seeds and read up on why they do great with tomato and pepper plants but don't know if I'll plant between my rows as I mulch with straw but will plant them as a border around my garden.I have the Queen Sofia variety.I always plant Basil with my tomatoes,I think that will go between my peppers and tomatoes in a row of it's own.