I have been planting tomatoes out in April for quite a few years since discovering plastic double-walled tunnels. I looked at 30 year temperature lows for April and there was only 2-3 degrees difference between April 1 and 15, so even tried moving the date to April 1, but this year I didn't get plants hardened off early so planted some out on April 15. They had gotten too tall for my 11" light shelf clearances, so went into my aquaponics grow bed transplanted into 4" pots for several weeks, and got rather leggy there. I harden them off on my east-facing concrete front porch, where the morning sun doesn't burn the delicate foliage and the concrete acts as a heat sink.
I went through several years of extensive tomato trials of 60-100 different heirloom along with a few commercial or hybrid varieties, and found some I liked, but many were in the 72 and up DTM (Days to Maturity) range, which here can be 2 times as long. After 2 years of very cold June and July temperatures, in addition to our usual cold summer night temps, near 50 degrees F, I decided the only way to make it worthwhile to do all the work was switch to early varieties and also a number of determinate varieties that don't require as much support and time-consuming tying up.
The 3 varieties going out first are Juliet (F? saved) vigorous producer of small paste cherries; Jetsetter, very early and productive small, round and blemish-free; and progeny from what was supposed to be Napoli but wasn't, but was a great little tomato last year, blemish-free, productive and in clusters. I hope its offspring will resemble it-
Plants I am continuing to transplant and harden off will be New Big Dwarf, a rugose good producer; Legend, taller but late blight resistant, nice blemish-free round slicers; Martino's Roma, determinate and productive paste tomato; old favorite Verna's Orange Oxheart, wonderful fruity heart with that delectable meaty texture; Lucky Cross as a gamble because last time I tried they didn't come true, but it is a luscious bicolor, longer DTM; and a saved paste which may have San Marzano as a parent.
The experiment I tried last year interplanting bush beans with tomatoes and eggplants, utilizing the poisonous quality of the nightshades to potentially repel the voles, seemed to work great with little damage to any beans or plants, so I will repeat that again, which is another motivation to plant short determinate tomatoes that won't shade the beans as much.
Back to transplanting, Hannah