I'm in similar circumstances in PA, but luckily just with lettuce and cole crops. Happens to me every year. My plants are small, so I have them covered with milk jugs cloches. Tomorrow, I will run Christmas lights (small worked last year, trying the large ones this year) between the plants, then cover everything with a frost tarp (canvas painters tarp). The lights definitely increase the temperature under the tarp. I don't know if it will be enough to save tomatoes, but it is worth a try. I posted recently with a picture of my plant-tent city. I've included a link below. Let us know if you are able to save them! Good luck tomorrow, Bellatrix Here is a link that might be useful: Frost Cover Tent with Christmas Lights picture

I'm really late with this reply, but maybe it will help you next year. I keep Christmas tree lights in my fruit trees. The kind with the large bulb; the fairy lights won't help. I have the lights on a thermostat, to go on automatically when temps get down to 40 degrees. It's not a huge help, but I figure it gives me a couple of degrees more leeway, and that's often just enough. Blossoms won't normally get damaged until about 29 degrees, so if I can protect them to 26, it covers almost any spring freeze we have. If you only have 1 of each type of fruit, your problem might be lack of pollination rather than frost. 100% probability that the plum problem is lack of a pollinator. I'm supposed to be zone 5, but that's a joke. Weather is much tougher than zone 5. I'm getting fruit, so I can't see why it would be too cold in zone 7. It's May 5th and there is snow and hail going on outside my window right now. I plant cold hardy varieties and get the latest bloomers I can find. Late blooming will make a huge difference in whether or not you get fruit where there are spring freezes. I suspect I lost the crop on my earlier blooming apricot. We had several night with temps in the teens right after it bloomed. But the apricot that blooms 2 weeks later has lots of tiny baby apricots on it right now.

I once lived in a similar night time climate elsewhere in CA. Frost some/many nights into as late as April. It seldom dropped below 28F. There was little to no damage on citrus. But if you are concerned with small trees you could cover them with light to medium weight frost blanket. It could stay in place all winter as long as it doesn't exclude more than 50% light. Basically if your trees aren't growing in winter they will be OK. So don't push new growth with fertilizer or excess water late into fall.

Fescue sprouts will be just fine down to 25 and might like a light sweater below that. Maybe. I'd definitely use straw at 20, but even that's unlikely to do much damage. Forty? They won't even notice it. Growth will stop until the ground and air temperature warm again, but that's about the worst effect you'll see. Grasses, like us, are mesophiles (moderate temperature life-forms), but grass actually likes it cooler than we do. To them, fifty is quite comfortable, forty is no problem, thirty is a might chilly.