Hello,

Most of the year I grow my citrus in containers in the greenhouse, along with dozens of other ornamental and fruiting tropicals. This past summer, I moved my container citrus outside. I had done lots of reading on thigmomorphogenesis and I developed the idea that the added light and wind and possibly other factors might help the trees.

I am favorably impressed with the results. No pest problems, aside from a tiny bit of hopper damage. Good growth. Dense, dark, healthy foliage. More oranges than in three previous years combined.

I wonder what others do, what observations they have made in regard to keeping trees in the GH in the summer versus taking them outside.

SB

on top of everything else - wind stimulation and higher light levels - I believe the carbon dioxide levels outside in fresh air are going to be higher. I always try to think how a plant has been living for millions of years -before we came along and started messing around- and let that steer my actions.

Plants did not evolve in green houses.

I always move my trees outside during the summer months, and they have always benefited. Due to various predators insects, that are not inside the greenhouse, the trees have less bug problems, plus the temperatures are not as hot as the summer heat inside the greenhouse. Caution must be taken to guard against the containers becoming to hot from the sun's rays, and in Colorado from hail. The flicking back and forth of the trunk and branches by the wind is natures method of strengthening the tree. Its analogous to exercise for humans. All seedling trees should be subjected to the wind or artificially by the use of a fan starting at 2 inches in height. In side the greenhouse during the winter months, I always have 5 box fans going day and night.

I agree with Millet.....I have from time to time, given my container trees a strudy shaking to promote stronger root growth.

When we were in greenhouse tomato production, this is how we pollinated the plants...instead of "flicking" every bloom...give the plant a sturdy shaking...pollination & increased root growth at the same time.

I have been known to "bump" a poorly producing pear tree with the bumper of my truck ...worked like a charm too....

Right. The beneficial effects of the movement...perturbation in some literature...is part of the thigmomorphenesis I mentioned above. The literature is fascinating. There are all sorts of beneficial effects, from improved disease resistance to better stem/trunk strength.

I think taking them out is good for them. Usually, I take all my potted plants out for the summer. This summer I took some out, but didn't get around to getting all the citrus out of the greenhouse. The ones left inside had no blossoms, although they did grow some. I noticed while bringing the others in this fall, my Eureka lemon was a rich, dark green & loaded with buds. (And no bugs) My first home grown citrus was a Meyer lemon 2 years ago. That one also flowered after bring it in for the winter. BTW, I've grown all my citrus from seeds.

How about very hot climates? In summer, here, the sun is really powerful and some of the citrus trees have leaf burns.

It is the first year that I will grow seedlings in greenhouse and I was planning to keep them in greenhouse at summer.Actually, I will keep them in greenhouse until late April.Then I will move them out to enjoy open air for 2 months, May and June.Then I will move them back to greenhouse BUT I will cover the greenhouse with a shader and will open the sides of the greenhouse.So that they may get enough wind plus they will be protected from direct sun.

Do you think it will work fine?

I don't have a greenhouse anymore, but to protect my citrus seedlings from the scorching sun this past summer, I set up a shade cloth-- just draped over a fence and a table. I have had the shade cloth a long time and do not remember the shade factor, but would guess it is about 60% shade. As it turns out this was a great place for the seedlings for winter in our usually mild climate-- they have remained under the shade cloth all but 3 or 4 nights when the temp got into the mid 20s F (-3 to -4C). I have taken some of the key limes inside a little more often, but some hava actually stayed outside under the shade cloth in low 30s F without any sign of damage or leaf drop. Some of the smallest clementine seedlings were even left out in the mid 20s with no protection other than the shade cloth and were completely undamaged.

Bottom line is a shade cloth works for me almost year around.

Thanks Skeeter,

I will use the shade cloth on July-August and September.
I think seedlings will need full sun when they are too young so I believe it is better I keep them in full sun in May and June, do you agree?

I am sure shade cloth will not cause a problem if I use it in May and June but maybe it can slow the growth of seedlings.

The more important factor regarding growth of citrus is not the sun's rays, but rather the temperature. At temperatures above 96F (35C) growth of Citrus slows way down or stops. The altitude of my farm is 5,440 feet (1,814 meters). Therefore the intensity of the sun's rays is extremely high, among the highest light intensity in the United States. Due to the intensity of the sun here, Colorado has one of the highest skin cancers rates in the country. Personally, I have never had any problem with leaf burn to any of my trees that have acclimated by continually growing in direct sun light every day through winter, spring, and then summer light. However, the water content of the soil or container is very important when the tree is experiencing both high light and temperatures. - Millet

I don't think the shade will slow growth very much at all-- in fact even with all this cold we have had lately, many of my seedlings are in the middle of a new flush (because I used slow release fertilizer and we had a very warm Dec). I don't know the exact number, but citrus leaves reach their maximum photosynthetic rate at somewhere around 30% of the sun's maximum intensity.

While citrus is capable of growing very well in full sun, it does not have to have full sun for maximum growth. Citrus evolved as an understory tree and has developed the ability to utilize light efficiently.

You can do your own experiment-- put some seedlings in full sun in May and June as you plan and put some under a shade cloth.

Skeet, citrus photosynthesis maximizes at a light range in the area of 650 PAR. I agree that citrus does not require full sunlight to grow well, but I think citrus produces more fruit when grown in full sunlight. As Meyer Lemon is growing seedlings and not fruit production, my guess, as far as growth is concerned, he will have more trouble from the heat than for the light. Citrus grow best at about 80-86F. I have been to a lot of different foreign countries, but I must admit that I have never been to Turkey, but I think it would be a neat place to visit.- Millet

But citruses, being C3 plants, reaches photosynthetic saturation far below the full sunlight level, given certain temperature. So full sunlight under certain conditions is actually not helping except to heat up the plant to stressful levels, depending where you start with.

650 PAR is about 30% of full sun intensity in this area (about 2000 to 2300 micro-moles PAR /meter square/second)-- if you live in an area of higher intensity then it could be less than 30%.

Joe is correct regarding excess PAR, at least for most plants that I am aware of--it can damage or wears out the photosynthethetic complex quicker and causes the plants to have to make protective compounds such as carotenoids and xanthins.