On a 36 degree night if it is clear and calm I would expect to get a light frost. Yes you can use a tarp to cover the plants but make sure the tarp does not touch the plants as the tarp will conduct the cold to the plant leaves. Make sure to remove the tarp in the morning before it warms up too much. I've never used a heater to protect from frost so I'll let someone else comment on that.

When I'm about to panic I bring out the huge stack of five gallon paint buckets. Not only do they cover individual plants very well, they also act as supports for tarps or plastic painters' sheeting for extra shielding.

Just use the tarp. I have gone through two frosts here with tarps (yes, touching the plants, it is too much work to put up supports), there are two more frosts coming, the last one Friday. It is a bit of a pain to roll them on and off every day, but they work at 36F. Fairly comical, two days ago I passed in front of the local supermarket, they had hundreds of basil plants for sale outside. Yesterday I walked by the supermarket, the basil was all dead, despite the warmer microclimate due to the building and surrounding asphalt.

If the ground temperature is higher than the air temperature, a tarp is the way to go for light freezes. But you MUST seal the edges against the ground. That is, don't let outside air get under the tarp. Use rocks, wood, etc to do that. That's the only way you'll be able to hold onto the ground heat. If you have some more insulation (blankets, etc.) just throw them over the tarp.

Don't use a propane heater. That's dangerous in an enclosed space. Just run an extension cord under the tarp and put a few light bulbs on it if you're still concerned.

You can go with the tarp, but your going to have to take it off eventually so the plants can get some light.

What you really need is a row cover. Protects from light frosts, lets light in, can be used as insect control, etc etc. Row Cover is what most growers use to extend their season and protect their crops.

this is not a freeze, it is a frost. There is no need for heating and no need for sealing. Just the cover (the elimination of thermal radiation to the sky) is enough.

It's not an air temperature freeze. But if you have ice on surfaces (which is a frost), those surface, and probably your plants as well will be at a temperature that water freezes, which is simply not good for your plants.

Air radiates much less efficiently to space than solid surfaces do, so it's often warmer than the surfaces within it.

But that's correct, if it is just a light frost, a simple unsealed cover will probably suffice to keep the plants from seeing freezing temps. You need sealing if you have a harder freeze.

As to row covers, that's just an added expense and probably overkill for a 3x20 garden. Plants will be quite happy shielded from the sun for a day or two. Just pull it off in the daytime. You use a transparent row cover when it's a major expense of manpower to set it up and take it down.

I suppose you could argue it's an added expense, but for what it does, I don't think it's that hard to justify a small investment.

Here's an example, I covered this 4ft X 2.5ft strawberry bed in the late fall. We had the worst winter here in RI in 25+ years. Pictures were taken on May 2nd, and I picked my first strawberry on Tuesday May 19th.

We have a large pick your own strawberry growers a few miles away who predicts they wont have anything ready to pick until 2nd week of June due to the cooler than normal spring we have had.

To me, a few bucks is well worth it to get a longer growing season along with frost and insect protection.....along with some jealous neighbors. :)

Forecast yesterday was for a low of 34 and extensive local frosts. I put on a tarp and a heat tape intended to be wrapped around a pipe. It only got down to 43.
I guess that is good, but how incompetent can weathermen be! A wild guess would have been just as good.

In my experience, weather forecasting is done with possible extremes in mind, especially when it comes to frost. About five years ago we had a popular local forecaster who once predicted temps down to 38F. We had a hard freeze. The reaction from the local gardening (not just vegetable, but EVERYTHING) community was shock, hostility, and even abuse. The guy got his career handed to him on a cart. He left soon after. I think he's up in Denver now, where his unpredicted freezes can be more easily tolerated.

I agree that blankets and plastic sheets make suitable covers for vulnerable plants. You can use stakes to keep material, especially plastic, from touching leaves (as not to conduct the cold to the plant leaves). And you should remove the coverings when temperatures rise the next day. Honestly, I've never used electric heaters to help keep plants warmer. I used the old method of filling bottles with hot water and placing them around plants under cover. Old non-led lamps also work well to save plants from cold weather. As for me, I can't stand the cold either, so I use a heater like this one ( you can find it on https://dehumidifiercritic.com/best-heater-for-large-room/ ) to keep warm. And I can say that I like plants because we have a lot in common with them.