Sounds good. I can bring the temps down about 10 degrees and cut back on water a little but I've got tropical aroids and others under the same lights and I don't think they'd like much cooler temps. I might try relocating half my lights and putting up a divider with the veggies next to a window I can leave cracked.
I need a bigger house! lol

Mike,

"Greenhouse nurseries raise their plants under lower light levels..."

Really??? The sun is quite a bit brighter than my fluorescent light setup.

ZM

ZM,

Unfortunately, not in Cincinnati, at least not until March, early April. Plus, GHs tend to get about 70-80% of the light, less than that if they are using 2-3 year old plastic.

More than anything, it is the correlation of heat, light, humidity and moisture that triggers plant responses, whether it is adding more leaves and branches, growing thicker leaves, forming roots or stems. The article is here.

Happy New Year,

Mike

Very interesting article. Well written.

Thanks,
Jane

Mike,

That is an interesting article, and it explains the concept of the DLI (daily light integral), which is just the total dosage of light energy for a day. But I don't see that it recommends low light levels (low foot candles). On page 3, the best root growth is produced by the highest light level (0% shade). And it says that, "Many "shade" crops grow best under moderate to high light levels." On page 4 it shows that the higher the light level, the better the quality of Vinca plants. In Figure 3 the article shows that for Vinca and Zinnia that plant height, branching and flowering increased as the percent shade decreased.

In all of those figures the highest DLI corresponded to 0% shade. They didn't show an example where a higher DLI was achieved with a lower light intensity by exposing the plants to the lower intensity light for a sufficiently increased time duration. For a given lighting setup, you get more DLI by leaving your lights on for longer. You would get a higher DLI by leaving your lights on continuously, but some plants require a dark period.

They used Vinca and Zinnias as examples. The question remaining in my mind is how many hours per day should I burn my fluorescent lights for my zinnias for their best health? In my experience, the more foot candles my zinnias get, the better they look. That is why I pack my fluorescent fixtures as close together as I can get them, and overdrive the fixtures for brighter bulbs. I don't see that this article suggests that I do any differently.

ZM

ZM,

It doesn't recommend low light levels, but explains, in part, that low light levels alone will not cause legginess.

As far as how much light your zinnias require, a cool-white fluro provides .000524 mols or PAR light per hour per footcandle. Zinnias require ~18 mols/day. Thus (if my math is right!) if you run the lights 18 hours per day .009432 mols per FC so you would need about 2,000 FC or 21,500 lux.

At 16 hours, you would get .008384 mols per FC so you would need ~2150 FC or 23,000 lux. This is for high quality growth.

HTH,

Mike

Mike,

I monitor my fluorescent setup with a light meter, and even by keeping the fluorescents a few inches from my plants and by over-driving my fixtures, I am hard put to get 1000 foot candles on the plant leaves. I don't dispute your figures about the high light levels needed for high quality zinnia growth (although I haven't done the math). I do have an issue with your original statement,

"We've all heard about how lights need to be kept close to plants to avoid stretching. Jim Faust, perhaps the ultimate authority on lighting and plants, claims this is not true, but with caveats."

I think that with fluorescent lights you should keep the bulbs as close to the plants as is practical, and I don't think the article by Jim Faust meant to contradict that. It applies to greenhouse management, and not to starting seedlings indoors under fluorescent lights. The sunlight that is available to a greenhouse ranges from 5000 foot candles and up, and that is completely out of the reach of what is available to the average person starting seedlings indoors under artificial light, with the possible exception of expensive HID lights.

On page 6 of the Faust article, it says:

"Low light does not = stretch
It is common perception amongst grower[s] that low light conditions promote plant "stretch". Our data do not support this conclusion. In most situations, low DLI (produces shorter plants than moderate DLI environments (10 moles/day). Under low DLI condition, the plants lack sufficient energy to produce a vigorous primary shoot."

A plant that doesn't have enough energy to produce even a primary shoot is not a good thing in my view. That is a pathological situation that puts the plant in a near death situation. I think I will lower those lights as near to my plants as is practical, contrary to the first paragraph in this message thread.

ZM

ZM,

I think this is a case of "I know what I mean, but I didn't state it so others would" type of things. I firmly believe that the more light you can give a plant (up to a point) is going to be better. But at the same time, if one cannot provide enough light it doesn't mean the plants will grow leggy. Decreasing the moisture level, nuits and temps will keep the plants shorter and stockier, but they will not grow very fast.

I don't dispute your findings about the FC that you are getting but they sound quite low. I haven't used fluros in a couple of years, but I was getting about 3,000 FCs if I had the lights just a couple inches above the canopy and my bulbs were quite old. I looked at the specs for some new 4' fluros and several of them were listed in the 2850 lumens range.

I wish I could have got 5000 FCs in my GH last year. I checked the readings in September and October and in the best part of the day I was getting 4000.

By all means, keep your lights as close as possible. I do, regardless if they are 13 watt CFL or 600 watt MH!

Mike

Mike,

"...if one cannot provide enough light it doesn't mean the plants will grow leggy. Decreasing the moisture level, nuits and temps will keep the plants shorter and stockier, but they will not grow very fast."

Agreed. In light of your clarification, I think we are in general agreement now. Since we moved here this last Spring, I have my plant stands in the basement and I don't have any direct control over the temperature. But the basement temperature is a few degrees cooler than my upstairs indoor setup was last Winter and early Spring, and that may be a good thing. Our living area temperature at the other place was probably warmer than the plants needed.

My problem with indoor zinnias isn't that they grow leggy, but that they just naturally grow taller than is convenient in my plant stands. I have experimented with two plant growth regulators (Topflor and A-Rest) to control the height of my indoor zinnias, with some success. But I need to perfect my PGR procedures. Otherwise, I have to remove a shelf and have just two shelves in a 6-foot plant stand, and I have done that on several occasions in the past. I think I need a greenhouse.

ZM