Acceptable Lux Reading in Greenhouse

[PaulTandberg]

I have a little poly "tent-style" greenhouse I grow tomatoes in. It is several years old and last year the tomatoes inside the greenhouse didn't do as well as the ones outside. The plants were lush and healthy, but the ripening was slower than I expected. There could be any number of reasons for this and I had no fair one to one varietal comparisons, but I have begun to wonder if the aging poly is perhaps filtering more light out than it used to.

I just purchased a small lux meter from Amazon. In full sunlight the lux reading in the greenhouse was 45K while the reading outside was 80K. When some clouds rolled by, the lux lux reading inside the greenhouse varied from 17K to 23K while outside the reading were 35-40K.

In general, the lux reading in the greenhouse appeared to run roughly half of what the unfiltered reading would be. Is this enough light? Is this par for the course with poly greenhouses and is the amount of light fine for tomatoes? Is it time to invest in new material (and are poly tunnel type greenhouses generally fine for tomatoes)?

((I do live in North Dakota, so our daylight hours run long in the summer))

I understand that a simple lux meter does not offer the best or most complete reading, but a simple lux meter is what I have.

[Fusion_power]

Plants have to receive at least 25% of full direct sunlight to deliver the expected levels of energy the plant needs. You can derive the numbers from this. If 80K in direct sun, 20K should be enough to keep the plants happy, caveat that they need a minimum of 8 hours in full direct sunlight to give optimum performance. If they are getting less than 8 hours of light, the plants may show restricted growth and production.


I would lean more toward looking at the media the plants are growing in to determine where things are going wrong. A combination of restricted root volume plus any reduction in sunlight would be a double whammy.

[PaulTandberg]

Thanks for your helpful reply, Fusion.

I get great growth (and disease-free growth) in my little greenhouse.

Last year, I thought the maturity lagged a bit compared to my outside tomatoes. I didn't have any fair comparisons, but regardless , some seeds of doubt were planted. And when my little tester showed a 50% reduction in lux, I figured it was forum time.

Last year was prolly a quirk. This season I am doing a couple A/B comparisons and will pay more attention.

The major benefit I have noticed with my little greenhouse (8'X8') is there are no problems with leaf disease... all season long. It does need supplemental heat if I put out plants early in the season when nights threaten frost, so that advantage isn't as great as I had hoped (without supplemental heat, it actually seems to get a couple degrees colder than ambience during the nights I would worry about).

But, it is fun. A bigger one might be in my future.

Thanks for the help.

[MrsJustice]

Originally Posted by PaulTandberg

I have a little poly "tent-style" greenhouse I grow tomatoes in. It is several years old and last year the tomatoes inside the greenhouse didn't do as well as the ones outside. The plants were lush and healthy, but the ripening was slower than I expected. There could be any number of reasons for this and I had no fair one to one varietal comparisons, but I have begun to wonder if the aging poly is perhaps filtering more light out than it used to.

I just purchased a small lux meter from Amazon. In full sunlight the lux reading in the greenhouse was 45K while the reading outside was 80K. When some clouds rolled by, the lux lux reading inside the greenhouse varied from 17K to 23K while outside the reading were 35-40K.

In general, the lux reading in the greenhouse appeared to run roughly half of what the unfiltered reading would be. Is this enough light? Is this par for the course with poly greenhouses and is the amount of light fine for tomatoes? Is it time to invest in new material (and are poly tunnel type greenhouses generally fine for tomatoes)?

((I do live in North Dakota, so our daylight hours run long in the summer))

I understand that a simple lux meter does not offer the best or most complete reading, but a simple lux meter is what I have.

I had the same problem by experimenting with a large Heirloom Tomato Plants in my Greenhouse last winter. I agree with "Fusion" A combination a restricted root volume caused my heathy "Old Virginia Tomato Plant to produces 1 little Tomato as sunlight wasn't the problem at all. But I will Grow only "Red Robins Dwarf Tomatoes in my Greenhouse for the Winter Months only. So, the Size of your Plant Tomato Plant is important when selecting a tomato verity for growing in your Green House to grown in Large containers.