Row cover comes in all sorts of weights/thicknesses/weaves. So the amount of trapped heat will also vary greatly. Some are intended for frost protection, some for hard freeze protection, and some are insect barriers only with no frost protection provided. In other words, no one blanket works for all needs. If insect barrier only is your goal then tulle works best as little to no heat is trapped with it.

The brand you name is not one of the common brands used so unless someone has some personal experience with it in a climate identical to yours you will have to do your own tests.

The only way you can know how much heat your particular cover is trapping is to measure the internal temperatures with thermometers several times a day. Cheap $ store thermometers work fine - one near the end of the tunnel, one in the center. Compare those temps with the temp outside the cover at ground level and note the differences. Then you'll know how much heat is being trapped during the heat of the day and when and how you need to vent it.

Dave

I have often seen tulle suggested as a summer insect cover

It's going to depend on the sunlight penetration. I suspect with transparent row cover, it'll get pretty warm. But that's exactly right to just monitor the temperature. I just got a digital thermometer (sensor on the end of a probe) on e-bay for $3 with no shipping charge. Works great, though if it matters, it does read out in Celsius. If you're worried about it getting wet, just put the meter part in a plastic bag. I have a couple. Everyone should have at least one.

I'll definitely try to get one. I checked the temperature today in the middle of the afternoon (by check I mean I poked my head in and felt the air) and it seemed fine. I'm including a pic of the fabric so everyone can see. Unlike the picture, my fabric isn't actually touching the vegetables. It's on a set of pvc pipes around the bed, but I digress. I'll get a thermometer soon just to make sure but I think so far it's going ok!

I think you can tell just by looking at it that it is going to trap more heat than tulle would. As a very general guideline air temp under row covers will be 10 degrees higher than out side it air temp. Often the difference is much greater. So if you are still getting temps in the high 80s I would be reluctant to use it at this time, especially if the covered vegetables are cool weather crops that don't tolerate heat without bolting.

JMO

Dave

Well, warm temperatures are fine for cool-weather crops as long as those crops aren't mature. In fact, it really speeds them up if winter crops are planted in the heat of the summer. We're in the 90s here, and my 6-inch collards are going super-strong, as well as my seedling beets and peas. But in a month or two it'll turn cooler, and they'll be better off for the head start. But certainly if you're thinking of covering mature crops that are prone to bolting in the heat, I'd avoid it.

The turnips and beets are about 2 inches tall right now, is that too big?

I'm pretty sure that turnips don't bolt unless they've gone though a winter. They are a favored source of summer greens. Beets don't grow well when it's REALLY hot, but won't tend to bolt unless mature. But everything grows faster when it's warm. The issue is keeping the temperature low enough not to kill the plants. Just to be safe, I'd try to keep the temp under 90F. Re cheap digital thermometers from e-bay, just don't order them from China (which you can get for a few pennies, really) if you need it soon. The delivery time will be a month or more.

With root crops it isn't just keeping them from bolting. It is also getting some root development started rather than just lots of top growth. This assuming you are growing them for roots rather than just tops. Excess heat encourages rapid top growth so if tops is the goal, no problem. If you want beet and turnip roots of any size then shoot for lower temps.

But this is all just speculation until you first determine what the actual temperature in your tunnel is and that means buying thermometers and doing it now.

I checked and In another post it appears you indicated you were already using tulle so why switch to the heavier fabric now?

Dave

But roots don't start to form until a month or two after germination. So by then it's going to be cool. Stands to reason that if you have good top growth by then, forming roots will be a cinch. Dave, are you saying that high temps for seedlings resets the plant so that it won't ever produce good roots? I've never seen any evidence of that.

Hi Dave, I switched from the tulle for a couple of reasons. 1. The fabric was getting chewed/ripped and the holes were still letting in some bugs which ended up getting trapped in the vegetable bed while I was at work. and 2. because the tulle I find is too thin to be spread across the pvc pipes and I have no sewing skills to join them together but mostly it was reason 1

" Dave, are you saying that high temps for seedlings resets the plant so that it won't ever produce good roots? I've never seen any evidence of that."

Just look at all the discussions about "why no root development on my radishes" or the ones on "my beets didn't develop any roots". Happens with all sorts of plants. Even tomato seedlings will grow long and leggy tops with minimal root development in excess heat.

Plants grow in cycles. Those cycles have genetic triggers that are affected by ambient and soil temps just as they are by water and nutrients.

Dave

Sure, no root development DURING warm conditions. But that's not what we're talking about here. We're talking about sprouting during warm conditions and maturing when cool. I plant beets at the end of summer when it's hot, and I have no trouble harvesting nice roots in January and February.

I should add that in doing such planting, you have to be really careful about soil temps. Seeds of any kind (winter or summer) can get baked when the sunlit soil temperature greatly exceeds the air temperature. I get bare soil temperatures in the summer in full sun that are pretty scary. But that's an issue about germination, and not root development.