Tip of the Week  #20

Authors Note: The following is written by someone who lives in the north eastern U.S.A. If you live in a southern climate, please read "Tip of The Week #21" when you finish this one.

The previous "Tip of The Week" about wintering temperate bonsai indoors ends with the sentence "Watch for signs of new growth as spring approaches.   As it begins to appear, more direct sun will be necessary. Coincidentally, in an E-mail today, Frank from Lanoka Harbor, New Jersey asked about sunlight.   He wrote:

Hi Paul,
In reviewing my literature it basically says that, bonsai should be kept outdoors (I'm talking summer).  However, I have conflicting statements as to sun.  Three views:
1) All should get a few hours of direct sun each day.
2) All should get filtered sun each day.
3) Needled evergreen should get part to full sun deciduous trees and sub-tropicals should get filtered sun.  Can you clarify this for me.
Thanks,
Frank

If you read 10 books, you will get 10 opinions because that's what books are, the authors opinion. Even "scientific studies" have to be interpreted, and the authors personal experiences always come into play. Well, here comes opinion #11, mine.

From spring to fall, all of my established bonsai (temperate, sub-tropical, deciduous, conifers) are kept in a location where they are exposed to full, direct, all day sun. The freshly potted ones are kept where they get only "slivers" of sun the first two weeks, diffused sun the third & fourth weeks, and full sun thereafter. If I see that a particular bonsai is not doing well, I'll move it to a place with a bit less sun, watch it and re-evaluate it's position every week or so. It is important that a bonsai that is kept indoors be put out as early in the year as weather permits.

The reason is that trees get "sunburned" just like people. They need sunlight for photosynthesis, and once the maximum needed on a daily basis is reached, the tree will begin to build a protection around its foliage. Much like suntan in humans, the trees coating will increase or decrease slightly on a daily basis as needed. This phenomenon is desirable in bonsai because each type of tree will produce a unique color when it is "sunburned." Junipers will turn blue/green, Rheingold Golden Arborvitae will turn a golden color followed by a beautiful pink. Red Maples will turn redder etc. In addition, the leaf/needle size of a bonsai is directly affected by the amount of sunlight it receives the more sun, the smaller the leaf/needle size. Conversely, the less sun, the larger the leaf/needle size. We bend over backwards to get smaller leaves & needles. Here's an easy way to achieve that goal.

A bonsai that has spent the last 6 months indoors has very little protection from the sun. If put out in full all day sun in July the results will be similar to a person from a cold climate going to Miami in March and laying on the beach all day. Hospitalization. The angle of the sun (and the effect the sunlight has on everything it touches) increases each day from late December to late June. When moving bonsai from their winter to their summer location, move them as early as weather permits. For the first week or so, try to find a spot where they will be exposed to morning sun only. It is less intense than afternoon sunlight. Check them daily. If after a week or so there are no signs of stress, move them into a location that receives more sun. Continue this process until they are getting the most sun you can give them.

It is important to remember that with increased sunlight comes the need for increased watering for two reasons. First, more sun dries soil more quickly, and second, more sun means an increase in photosynthesis, which means that the tree will need to draw more water from the soil.

If you are a "plant person" and the thought of putting a bonsai in full sun worries you, remember that "house plants" are actually ground covers in their native environment. There are small shrubs, large shrubs, small trees, and large trees growing over them. The have evolved in a place where they never see direct sun, except for an occasional tiny sliver. Trees, on the other hand don't grow in shade, they make shade. Above all, always remember that a bonsai is a tree, and it needs everything that its full sized counterpart needs.