Lemon trees and distance to light durning winter

9 years ago

last modified: 9 years ago

Hi,

I got a 250W CFL light with an reflector that I just bought to use on my
two 3foot lemon trees as the single source of light during the winter,
do anyone know at what distance from the tops I should place the light?
I'm keeping the room at 14-15degrees.

Also, I understand that the
trees go semi-dormant during winter, will more light during winter
season help my trees grow or will too much light take
it out of the semi-dormant state and into summer state making it stressed?

Featured Answer

Silica

9 years ago

last modified: 9 years ago

There is a phenomenon that affects citrus grown in containers known as WLD (Winter Leaf Drop) which is what happens to the trees during storage in winter quarters. Before cold weather, most citrus trees are placed outside where they can enjoy the summer sun and heat. With the appearance of fall and a decrease in temperatures, the trees are brought indoors to protect them from freezes and frost damage. The most common recommendation for storing the trees indoors normally goes something like this::

Give the tree as much light as possible, keep the compost moist, but never over water. Let the compost dry out more than in summer. Hold the tree at temperatures around 5-10 C (41-50 F).

If you have followed this advice and have had no problems, you are very lucky because most people who did so had problems. The trees start to shed leaves, leaf after leaf drops and in spring, after the last frosts, when the trees are placed outside again, many trees have no leaves remaining on the limbs, twigs and branches. The cleavage is often between the leaf stalk and the leaf blade, the stalk remaining on the tree. Often the dropped leaf shows no chlorotic patterns or any other discoloration. Our first thought was that Winter Leaf Drop was influenced by low-light conditions during winter times in Europe. But even with extra illumination Winter Leaf Drop continued. Often, after bright, sunny mid-winter days, more leaves are shed than after longer periods of less bright light. So we tried to find out what might be the cause of Winter Leaf Drop. We chose five "primofiorre"" lemon seedlings, all about one foot high. Those seedlings were placed in different locations with different conditions:

1. The first seedling was placed in a cool and bright location at a south-facing window, at temperatures around 6-10 C (43-50 F).

2. The second seedling was placed in the same room, but at a north-facing window.

3. For the third plant, we chose a temperate room with temperatures around 15 C (59 F).

4. The fourth seedling was placed at the same temperatures but on a south-facing window.

5. The last plant was placed in a warm room of 21 C (70 F) at a south-facing window with extra illumination.

All trees were irrigated as needed, just to keep the root ball moist, but not wet and not allowed to dry out. Only #5 was irrigated more regularly and fed evenly. After winter we found that #1 shed nearly all its leaves, #2 dropped some leaves only, and the others had only lost some (fewer than five) or no leaves. We found light may not be the factor causing WLD, so we thought about temperature.

After a long discussion with citrus experts in Florida and Israel we found that temperature will cause WLD. The temperature tables from the book Biology of Citrus (Cambridge Press) show that citrus seems to stop root growth and root function if the soil temperature drops below 12.5 C (54.5 F). Leaf activity will be reduced if the temperatures drop below 18 C (64 F). Leaf activity means the full process of water evaporation for leaf surface cooling, energy transformation (photosynthesis) and starch reduction for building amino acids and other compounds for forcing plant growth and cell development. Citrus controls its leaf temperature by evaporating water from the leaf blade. This reduces the temperature even during hot periods and will maintain the leaf temperature at the optimum levels between 25 C (77 F) and 35 C (95 F). But even on cold days the sunlight can heat up the leaf surface quite quickly to levels beyond the critical temperature of 12.5 C (54.5 F). Photosynthesis itself works better in cooler conditions with high light radiation than in the warmer periods of the day, so most of the photosynthetic starch production is done in the morning before noon and less water is evaporated than during the afternoon. Optimum leaf temperature for photosynthetic activity for most plants ranges from 10 C (50 F) up to 32 C (90 F). Photosynthesis itself needs carbon dioxide, light and water to transform the carbon dioxide into starch and oxygen. During the night the starch will be oxidized to provide energy needed for plant growth and development. The whole process is called breathing. Water and nutrients for the breathing process must be taken up by the roots. Oxygen and carbon dioxide will be delivered from the air around the plant, taken up by the leaf surface (and to some extent by other green parts of the plant) so leaf and root activity must run in a balance to provide the best plant performance for growth, flowering and fruit development. If a citrus tree is stored at temperatures below 12 C (54 F) but gathers enough light for photosynthesis, this balance is broken. The leaf activity requires water, which the roots cannot deliver. The plants stop evaporation and water will be unavailable for cooling the leaf surface on bright days, so the plant reduces active leaf area by leaf abscission. This seems to be the best theory about what causes WLD.

Partial or complete defoliation was never critical if the root ball was kept more on the dry side, but if it was too wet, a quick root decline developed even if Poncirus trifoliata was used as a root stock. Most of the trees recovered quite well in spring (if the roots stayed healthy and a heavy bloom was set). But in recovering the whole canopy, often the trees used up much of their starch reserves in the stock, which did not fully refill during the short summer times. After some years, many trees suffered, growth was stopped and the trees died because all of the starch had been depleted.

So what to do about WLD? Irrigation during wintertime seems to be a recommended practice to slow down WLD. Irrigation with warm water 25-32 C (77-90 F) supports the root function, even the water uptake, so WLD will slow down. Irrigation reduces the plant stress during cold winter time and is therefore recommended.

Keeping the trees in a room with high humidity seems also to slow down WLD

but cannot prevent it. Also a place more in the shade, to minimize leaf activity, slows down WLD. Keeping the root temperature below 18 C (64 F) but at or above 15 C (59 F) seems to work best for stopping WLD. The plant functions are minimized, but water and nutrient uptake for leaf activity is high enough to support the breathing process and leaf surface cooling by water evaporation.

A mild winter chlorosis (yellow veins, dull-green leaves and sometimes weaker growth) may develop, but this will disappear in spring with rising temperatures. If WLD persist, you may force the root temperature is little bit higher, around 21 Â¡C (70 F) Sometimes during the winter, fruits dry out on the tree and drop if the tree is stressed too much. So for fruit development and fruit maturity, higher temperatures and good leaf activity should be maintained. Irrigation with a nutrient solution should be done even in winter.

But never forget: The best care for your plant is what your trees tolerate without critical losses of leaves and fruits. If trees look quite good in conditions different from those mentioned here, do not change your care. But if your trees suffer, check your conditions and your care schedule and change cautiously. Avoid fast environmental and care changes. Greater changes should be spread over a longer time period to give the tree a chance to adapt.

Johann Chr. Volkamer, writing in 1714, recommended keeping the roots warmer. Volkamer, who lived before modern conservatories, set his trees in glass houses where the pots were surrounded by horse and cow manure. This manure, if kept moist, started to rot and this rotting process set free some heat, which kept the roots warm, beside also feeding the trees even in winter. So Winter Leaf Drop was avoided during the 18th century by manure packs around the container and a more shaded location (because the glass was not as transparent as it commonly is today). Volkamer has even written of heavy fruit wilting that can be avoided by the manure packs, which illustrates what cold stress does to a citrus plant. Cold-sensitive varieties like citrons, limes and some lemon varieties are more prone to WLD than sour orange, oranges and mandarin-type trees.

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Comments (22)

myermike_1micha
9 years ago
Stephan, from my experience, I hope to share..

You are right, by nature they do go semi dormant and get ready to push new flowers and fruit..Mine always do better than those I gave artificial light to. They pushed out new spindly growth and get infested with bugs. I had lower fruit yield, dropped fruit and less vigor..Leaves would grow distorted, less turgid, and wrinkly...I could never give enough light to match what the full sun could provide..

That's why if I can't provide FULL sun all day in sunny south facing windows for my trees, I don't buy that many to force the rest under lights..But if I had a window for everyone of my trees with full sun only, I would buy a mass of them. But I do have the advantage of providing them the rest period they need by placing them in a cool well lit room. Other I can put on a window sill, and yet they too still get very cool by night there preventing leaf loss and twig die back..

Does that make any sense?
Steffen Birkeland
Original Author
9 years ago
Hi,

Im from westcoast Norway and the sun wont come over the horizon during winter early November - mid Februry:( Two months on each end of that they sit by a sunny window in my house, and May-september they are outside:)

I read on some online guide that there where 3 basic strategies for the winter period, approx. 8 degrees with little light, 10degrees with more and 15degrees with alot of light, I got a insulated room in the garage where i keep my trees, I use the room as a gym and with the spare heat from the light (14hour/day), combined with a little oven and a fan on a thermostat I can keep it at 15degrees which is ok for working out.

My questions is, what is alot of light and how close do I need to bring the 2700k CFL to the top of the plants? now they are at 40cm.
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myermike_1micha
9 years ago
Steffen, Ia m sorry no one has come back to answer for you, but hopefully someone here knows about the proper lighting more than I do..
Laura LaRosa (7b)
9 years ago
I know another Stefan on this board is lighting expert. Hopefully he will see it if he is around.
myermike_1micha
9 years ago
Silica, great info..I tried to find this info because I have seen it before and I think it is very thougful for you to find it and post it..We can take a lot of pointers from this and I appreciate it..No one knows our trees more than we do and understanding how light and temps affects leaf loss is like gold..

Have a good night and thanks again! I will have to re read this since I can't remember everything.
cory (Zone 7a, NJ)
9 years ago
Thanks Silica.

Cory
Steffen Birkeland
Original Author
9 years ago
Thank you Silica! :)
Laura LaRosa (7b)
9 years ago
Thank you Silica! I will re-read it later to fully absorb everything!
myermike_1micha
9 years ago
last modified: 9 years ago
This is the category I fall into....I can now understand why I never have any leaf drop in the porch with indirect sunlight or in my greenhouse with very high humidity..Then in my sun room I never allow the temps to go above 65 degrees..I discovered this works way before this article was ever seen by me about a year ago..I am glad it confirms what I do and what I have suggested others to do.

"Keeping the trees in a room with high humidity seems also to slow down WLD

but cannot prevent it. Also a place more in the shade, to minimize leaf activity, slows down WLD. Keeping the root temperature below 18 C (64 F) but at or above 15 C (59 F) seems to work best for stopping WLD. The plant functions are minimized, but water and nutrient uptake for leaf activity is high enough to support the breathing process and leaf surface cooling by water evaporation."
Steffen Birkeland
Original Author
9 years ago
Thank you
gain! Truly interesting reading!
So it looks
like I’m pretty close with my setup, but my questions remains; At what distance
should I place the CFL light from the top of the plant? (12hours/day as the single source of light)
Silica
9 years ago
last modified: 9 years ago
I use a stronger light then a CFL. I use a Medal Halide light. At the beginning of the lighting season I start with my light approximately 6 inches above the tree. Then move it closer ever couple days until it is about 3 inches above the foliage.
User
9 years ago
last modified: 9 years ago
Thank you silica for the post on WLD, which appear to be your words but they are not and you did not provide the reference to the article. In other words, you plagiarized it. The original article, written by someone else, is found here: http://www.steffenreichel.homepage.t-online.de/Citrus/WLD.html

By the way, the process referred to in the article as "breathing" was poorly translated from the German. It is "cellular respiration".
Silica
9 years ago
last modified: 9 years ago
Vladimir, I agree that I should probably have included a source, however, that article has been posted on forums a 100 time in the last year or so. Everyone one should have known about that article several times by now. However, your correct, proper care should have been taken. Thanks
User
9 years ago
No problem, silica. I do appreciate you bring it our attention. Thanks again.
cory (Zone 7a, NJ)
9 years ago
Silica, Thanks for posting that information again. I have read it before several times but even so I almost made the mistake of lowering my greenhouse temperatures at night to 50°F and I most likely would have gotten WLD as my greenhouse is in full sun. I have been keeping it about 63° F for years because I had warmer growing orchids in there but moved them out thinking I could save money on heat. I know better but just forgot thinking of the possible heat savings. I want to keep my trees growing as I enjoy the blooms and watching the growth spurts so I will make sure the soil around the roots stays above 54.5° F. My trees are finally recovering after their complete defoliation after my April greenhouse overheat so I am glad to avoid further defoliation stress.

I believe the slight nutirient deficiency showing on the leaves of my more cold sensitive trees such as lemons, limes, clementines, Tango, Page Pixie, Kishu and W. Murcott mandarin could be due to the cold night temperature spells that occured a couple of times for several nights in a row although the temperatures have mostly been warm this fall. Night temperatures dropped to the mid-thirties a couple of nights in a row and the early morning sun was bright and day temperatures only rose to the 50-60°F range so the roots probably were not working as efficiently as it took a while for the container mix to warm back up to 55° or above and it showed up on the leaves. When the night temperatures got warmer again the leaves greened up again between those colder spells. I noticed the leaves showed the slight deficiency when the night temperatures dropped again, and again improved once the night temperatures rose to the mid 50s and 60s again. The leaves on all my other trees that are slightly more cold tolerant did not show this stress. I decided to bring the limes and lemons into the greenhouse before the night temperatures drop again and start to bring in the other citrus trees based on their cold tolerance. As U have a lot of trees it is nice to be able to spread the migration to the greenhouse over a few days as it is very tiring. I would have liked to keep them outside longer, but there is no sense to do that if I want to keep them actively growing instead of semi-dormant.

Cory
PacNorWreck
9 years ago
I just wanted to thank Silica for posting the above information as well. I had a devil of a summer with my lemon and lime dropping leaves even long after they were bare-rooted and repotted into 5-1-1 with Repti-Bark. We have long, bright days here in the PNW during the summer and the leaves would have been receiving copious amounts of light while the roots were hovering around 54-55F each morning. The two plants that struggled for me were also both in air-pots, which I imagine would have increased the roots' exposure to the cool night and morning air. There were a great many days during our cool summer this year where temperatures didn't rise above 55F until a few hours after sunrise. Is it possible that my lemon and lime (already stressed from some leaf drop and
the re-pot) may have had something similar to WLD happen?
Silica
9 years ago
Warm sunlight shinning on a citrus tree's foliage, and a cold root system, is the perfect scenario for WLD. If a tree begins to drop leaves, and you don't have a method of warming the soil, hanging a cloth in between the sun and the tree to shade the leaves also works.
PacNorWreck
9 years ago
Next summer I can move them to the opposite wall of my roof garden - they'll get much less morning sun and much more evening sun, which may be why my Yuzu (already along that wall) did so well this summer and the other two didn't. As long as they're small and easy to carry, I may as well take them inside for nights where the low is going to be below 55 too. Very informative, thanks again!
myermike_1micha
9 years ago
Pac..That is exactly what I do when it starts to get cold at night..I move mine to an area where they will get good sun after the temps have warmed up a bit and they love it..No leaf drop yet..

This is what I have been trying to say here for years..

Less sunlight the cooler temps should be.

If the temps are kept very warm, then indoors lights should be a must or a very sunny window that give sunlight for more than ten hours....

I have an Orange Tree that I have kept on my porch for a little over a month now that has done very well with very little direct sun on a cool porch. The sun being blocked by trees until the leaves fall for winter..Well, just yesterday it reached 80 here and the porch even warmer, and boy did I have massive leaf drop. It stopped now that it has cooled of again..

I discovered this WLD years ago when I use to keep my trees up in my plant room. I kept that room on the coolish side, temps never reaching above 65 with the windows cracked open all winter..One day my Dad put the heat on up there and the temps rose to about 74 and in just one whole day at temps that warm, most of my trees dropped their leaves just as described above..Once I shut the heat off and cooled that room off, the drop stopped! I learned something that day. That room is sunny too with a skylight, but not enough sunlight to prevent leaf loss in the dead of winter with temps that warm..So I figured the strategy on my own then I saw this article a couple of years later..Boy was I glad to see it!
Silica
9 years ago
last modified: 9 years ago
Mike is correct. If the tree's foliage is getting a LOT of sunlight, then the tree's root system MUST also be warm to avoid the possibility of leaf drop. If the trees leaves are not receiving direct sunlight, then the trees roots zone can be kept at a somewhat lower temperature. To be on the safe side at least a 60-F root zone temperature should be considered by the grower.
poncirusguy6b452xx
9 years ago
last modified: 9 years ago
My setup's

The tree un-canned
Notice the beet greens on the first floor. They heat the second foot base to 80F where the citrus trees' roots are. Box is 4 by 4 by 5 feet tall with 2.5 by 2.5 by 2.5 penthouse on top for the taller trees.

3 month old rooted Hardy Chicago fig tree cutting in light bucket.
Fukushu#2 in front, Fukushu#1 under yellow bucket. Sweetlee tangerine cuttings on top of yellow bucket to get warmth to rooting area with th white bucket on top providing light. In back to right is the Meiwa kumquat. Notice that the tree is too tall for the 2 bucket light and the lower bucket is held up with 3 sticks in the upper lip of th first foil lined bucket with the light containing bucket on top. New Zealand lemonade tree is to the left under trash can light.

Meiwa with light bucket removed and Meiwa both buckets removed.

Years past setup