My greenhouse is getting a shiny new covering of Palring 175

Normal plant growth takes 25% of full direct sun intensity. Even then, plants use at best 1% of the light hitting the leaves. Does anyone else still use Mols?

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As I understand it that’s about right for a single leaf of many broadleaf plants. Single leaves of certain grasses like corn and sugarcane can benefit from a higher light level. A plant canopy is a different matter. Because many plants have a leaf area index of 4 or more, the canopy benefits from higher light levels. Especially diffuse light that comes from all directions and thus penetrates deeper into the canopy of leaves.

Leaf area index is the total area of leaves per unit surface area. An acre of corn usually has 4-8 acres of leaf surface. A thick canopy of trees in a forest is probably about the same.

Fruit and nut tree canopies usually aren’t a full canopy like a forest. There are open areas between trees partly for access but partly because those trees don’t do well when the canopy closes over. The lower portions of the canopy become unproductive because the leaves are almost totally shaded out.

I’m sure you know all about why and when crops like pecan are thinned and/or pruned to open up the canopy.


yeah, and you have to buy the extrusions too, plus pay frieght from CA. Its pretty spendy, but performs well. Its anecdotally said to last 20-30 years. They give a 10 yr warranty

Palring has a 7 yr warranty. Solaring 6 yrs. I got 10 yrs out of the later. And that’s in a hot sunny climate.

The Solarig failed on the inner layer next to the bows. The outer layer still didn’t have a single hole after 10 yrs.

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Have you thought about applying a covering to the frames? Ive seen people use felt strips or similar to provide a bit of cushion and maybe distribute the pressure of the plastic against the frames


I have thought about that. But the cost and effort involved makes it unattractive. The cost would be at least several hundred dollars if I did it myself. And applying it would be a major project 16 feet in the air. A youngster might enjoy doing that. At my age I’d be lucky to avoid breaking something.

My total cost for a new covering was $1600. 900 materials, 300 shipping, and 400 for installation. It should last at least 10 years without protecting the poly. That’s $160 per year. I doubt that felt strips would add more than a year or two to lifespan. That doesn’t pencil out to me. Cost now and maybe a benefit in 10-12 years.

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We use foam pipe insulation cinched down with cable ties over the rub points (e.g., pipe intersections, and over the pipe where the angle changes between the roof and the wall). Not too expensive and doesn’t take too long to put up - still doing the peak is a bit dizzying. If I had a lot to do I’d set up a scaffold. Congratulations on your new greenhouse skin!


Thank you it is nice.

I’d have some misgivings about foam pipe insulation.

How long it would last? I doubt if it would make 10 years.

Would it damage the poly? PVC will.

And how I’d keep it up there while pulling up the poly. Each sheet of poly was 100 lbs. I had to use a fence wire puller to pull up the first layer. That bent my metal fence that I was pulling against.
It would have ripped off half the insulation and possibly felt unless it was really glued on.

I couldn’t believe how hard it was to pull the poly. And that was pulling over smooth steel. Anything rough would double the effort needed and possibly rip the poly.

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I’ve using that in a different application (thrip net cover in one case, bird net and shade cloth in another, each about 1/3 of the 96’ coldframe.

In our application, the foam is probably more exposed to sunlight than under your poly. It lasts about 3 years. Not a big deal for us since the coverings come down before the hurricanes and go up in the early spring.

Sounds like it wouldn’t work for your greenhouse. Good to know the covering is so heavy - maybe we’ll put off covering our greenhouse frame for another decade…

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Do you know how much light is needed for fruit trees, measured in PAR (Photosynthetic Active Radiation) and averaged to a DLI (Daily Light Integral). There is a an app called “Photone” which is pretty good and in the ball park of quantum sensor based measurement device.

DLI is an interesting concept. The Purdue paper discusses the needs of various floriculture crops but not fruit trees. For the crops discussed the DLI needed for high quality plants ranges from a DLI of 6 to 22. What I expect is that fruit crops would be towards the higher end of that intensity say 10 to 22 DLI. Things like berry crops at 10-15 DLI and tree crops 20+.

Given the outdoor DLI and characteristics of my GH covering I’d estimate my DLI at ~30 in summer, 23 spring and fall, and 13 in winter. I think I have plenty of light for any fruit crop. That’s what 20 years of growing experience says.

In Portland the outdoor DLI falls below 10 for 3-4 months in winter. That means you don’t have sufficient light during that period for many GH fruit crops. In summer you’re more like 40-45, plenty of light. In a greenhouse you’d be at ~5 for several months in winter and 25+ in summer.

My light in December is equal to yours in October and March. Yours in Nov thru Febr, four months is clearly suboptimal for fruit trees.

A greenhouse works much better here than in Oregon.

There once was a guy in SW Washington growing many fruit tree crops in a greenhouse all year long. He double cropped things like sweet cherries. But his fruit looked low quality and likely was.


Thanks, very informative post. I have used DLI as a key measurement to plant out my grow space in the yard and around the house. Used SpotON meter which uses a lower end Quantum sensor but relatively inexpensive compared to lab grade quantum sensors. Measurements were taken for couple of years from April-June. 30-35 is good enough for most summer vegetables, 40+ for tubers and winter squash.

Interesting that your summer DLI is lower, is that due to the latitude?

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Our DLI is higher than Oregon all year long. You are close in summer due to your longer daylight and less clouds. We are several times greater than Oregon in winter.

The phenomenon never crossed my mind until I got a greenhouse. That first spring I brought out all my seedlings to plant in the garden and they got fried in a couple of hours. That was the hard lesson that taught me about hardening off plants. I have noticed that some handle the transition much easier than others.


I had a few plants in the greenhouse that showed some heat/sun damage during the two days the GH was uncovered. Mostly newly transplanted mango seedlings. It was 100 outside those days and 109-112 by the temperature sensor in the GH.

In general, my GH has enough light/heat that well established plants taken outside don’t sun burn.

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Hi Steven.
It’s nice to see your greenhouse (I’ve been seeing photographs on the forum for years and admiring it).
It’s as big as the greenhouse of the nursery that sells fruit trees in my town hahahaha.
I have seen some photographs of the exterior of your home in winter, with enormous snowfall, and it is curious, because it is the complete opposite that a European could imagine of the climate of Texas, since the first thing we think of is men with cowboy hats. and semi-desert climate (the fault of the cinema).
Raising fruit trees on dwarfing rootstock in that greenhouse is the envy of everyone.


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3M Thinsulate could be an option if the motorized mechanism to roll/unroll can be made to work. Although, double layers are needed to get R10 level protection.

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