When is the right time to start planting outside?

Your early crops like loose leaf lettuce, kale, spinach should be out now......or very soon. Once your last frost day...probably mid to end of April...plant bean and carrots. Hold off a bit for the warmer squash plants, they truly want warm soil.....mid to end May?? I've even planted in June and done well. Tomatoes and peppers......have you considered purchasing a few of those instead of starting from seed? You'll get several weeks head start and a better chance of getting a full crop before fall frost. Of course you want the fastest ripening tomatoes varieties, not those that take 90 or more days.

I agree with Sew What. I've been in Maine near memorial day and it's only been 40 degrees. I have friends who live in CT and they start their lettuces and spinach now, with a hoop and cloth cover over it to keep the frost out.

To play it safe, probably memorial day weeknd or the weekend before it, would be good for you to plant all of your seeds which will germinate it a couple of weeks. I'd put tomatoes out the first week in June.

Where you live is the most important factor. You need to be asking your gardening neighbors this question. Also check in at the local garden centers.