What would I need to do if I wanted a citrus, that hasn't put out any new leaves in 5 months, to do that now? (It's summer here)

Fertilize & and make sure the roots are warm.

If the tree has fruit remove it, this will free up energy for foliage growth.

Ryan is generally correct (and by the way Ryan, the trees you posted on another thread were very nice healthy looking trees -- Great Job). To the point of this thread, many new growers eagerly look forward to the day when they can pick their first fruit from their tree, and therefore dislike removing any fruit in an effort to obtain growth of their small tree. Recently reading a Purdue University article on citrus growing, the article pointed out that it is OK to leave a fruit on a young growing citrus tree. Reading on, the article stated that one fruit will not delay in any way the growth of the tree. This is because a fruit requires the energy of only 3 leaves to bring the fruit to maturity. - Millet (561-)

Usually I leave the tree to select the fruits (drop off) but we know that not all citruses do that. If the tree stops to grow new twigs, then I start to remove one fruit every 2 weeks until the tree start to grow again.
Here is an example of lemon where taking in consideration the trunk diameter which is a bit thicker then a pencil, it have 9 lemons, drop off 4 and start to grow 5 fruits but in the last 2 months the tree doesn’t grow absolutely nothing. One week ago I remove the first fruit and now it start to grow again. The 5 fruit took too much energy from the tree and couldn’t develop any new twigs.

Evaldas, your tree is growing any fruit?





Evaldas, your tree is growing any fruit?

The trees are both Eustis Limequats. One is in a 12 cm diameter pot, the other - 15 cm. One tree (in a 12 cm pot) is blooming right now (seems to be doing just that for the past five months) and actually has 3 new growing leaves (but that seems little).
About a month ago I took off all the fruit from the other tree (in a 15 cm pot) but it still does nothing.
Take a look:

I've also pruned both of the trees quite heavily, but it didn't help.
Both of these trees in the winter time had been growing under grow lights, maybe that has something to do with that?
I start to believe that it is true that some citrus varieties are easier to take care of, I didn't believe this before. My Calamondins are growing putting out new leaves often without a problem...
I repeat, both of these Limequats haven't put out any new leaves (except for 3 leaves that are growing right now on one of the trees) in 5 months.

I think some clarification of the physiology of bud flushing may be helpful here. Statements above are correct, but I think they may be leading to the wrong conclusions. It’s quite true that a fruit gets its energy from only about 3 leaves. It’s also true that the presence of fruit may delay flushing. But this is NOT because of energy being taken or used by the fruit (another fun fact -- oranges take virtually no caloric energy from the tree after they reach golf-ball size -- the tree just pumps in water after that). Rather, it is the fact that the fruit is a source of auxin (indole-3-acetic acid) that causes the inhibition of flushing.

A bit of background here, on the nature of bud dormancy and bud growth: There are two competing hormones controlling the situation. The first is auxin, which is produced by fruit, flowers, leaves (especially young, expanding ones), and vegetative buds. This auxin is shipped downward via parenchyma cells among the phloem tissue. Axillary buds along the stem in some way perceive the passage of auxin downward, behind them, in the stem. As long as the flow of auxin is adequate, those buds will remain dormant. This is known as apical dominance, in that it is generally the bud or 2 at the end of a branch that grows, on most plants, while lower buds remain dormant; hence, the apex is “dominant” over those lower buds. This is easily demonstrated by pruning a branch at any point. Almost immediately, the next bud down from the cut will begin to grow, even though it may have remained dormant for years, until the cut was made. It is the sudden loss of that stream of auxin that told it to grow.

The other hormone involved is a cytokinin (mostly zeatin and perhaps some dihydrozeatin, in most plants), being produced by the roots and sent upward into the branches. Cytokinin stimulates bud break and flushing. So there is always a competition there -- cytokinin is telling the bud to grow, whereas auxin is telling it to wait a while. At any given moment, one message or the other is “winning,” and the bud will behave appropriately. So when the auxin flow decreases, the bud immediately begins to respond to the ongoing cytokinin message.

Back to the original subject here -- existing fruit. While they may be taking little or no sugars or other “energy” from their branch, they do serve as an ongoing and powerful source of auxin, so as long as they are present, there is a reduced likelihood of growth of the buds lower down on that branch. We also see this with “blossom blight” or “post-bloom fruit drop” disease, caused by Colletotrichum acutatum. It causes the petals of the flower to rot, then the tiny fruitlet abscisses. However, the calyx does not fall from the tree as it normally would, and instead, it swells and remains green. This calyx button is a powerful inhibitor of growth from subtending buds, and is part of the cause of damage to the tree -- not only did you not get a fruit from that flower, but that branch won’t grow again for many months, until the calyx finally dies.

On the other hand, fruit has this auxin effect only on buds located on the same branch, lower down on the branch. They have little or no effect on other, non-fruiting branches of the tree. So assuming the tree has a healthy root system (source of cytokinin) and the tree has adequate water and fertilizer, those branches should flush regularly. On a young tree, that may be every 8-10 weeks; less often on older, larger trees.

Wow, I'm going to snip off my empty calyxes right now. Most of my meyers lemons that reach the size of a small grape and then yellow and fall will leave the calyx behind. The ones that flower and drop immediately drop the whole flower bud. I was pondering this difference a few days ago. Most of my fruit appear to be at the size where they will continue to grow to maturity, but there are a few stragglers that do not appear to be gaining size that I think will ultimately be shed.

Dr. Manners, I know this subject had been raised before, but what are your thoughts on spraying cytokinins on the branches to affect the relative influence of the competing hormones?

Thanks for the info,

Barbara

Dr. Manners,
Thank you very much for these very usefull informations.

Previously posted above. >>>>>>" Recently reading a Purdue University article on citrus growing, the article pointed out that it is OK to leave a fruit on a young growing citrus tree. Reading on, the article stated that one fruit will not delay in any way the growth of the tree. This is because a fruit requires the energy of only 3 leaves to bring the fruit to maturity.<<<<<<<<<<<<

Purdue University does not go into all the detail that Dr. Manners provided for us concerning the auxins and cytokinins involvement on the flushing of a citrus tree. Therefore, to mesh Dr. Manners post with Purdue's post see below. Purdue says one fruit will not affect the growth pattern of a young citrus tree, which I feel is still true. However, as advised by Dr. Manners a fruit remaining on a tree can affect the flushing of that particular branch the fruit is attached to. Therefore, if a grower wishes to retain a fruit until maturity on a young tree, just note that that particular branch will not flush, but the balance of the tree will not be affected and should flush according to nature's system. I remember back when I was growing my very first citrus tree, how anxious I was to pick and eat my first fruit. Personally, now knowing what Dr. Manners told us in the above post, I would have gladly sacrificed the growth of one branch to keep my choicest orange. - Millet (560-)

Barbara, Certainly, spraying cytokinins on a branch can promote flushing. But I'm not aware of any cytokinins labeled for use on citrus trees for that purpose. Kinetin and 6-benzylamino purine have both been shown to have that effect in other plants.

Dr. Manners, your explanation reminded me of a thread that I found when I was introduced to the term "cytokinin" when trying to find GA in a tomato blossom set. Millet had indicated that tomato blossom set contained GA, but the formulation must have changed or the product that he referred to is not available to me locally. My blossom set for tomatoes contains the active ingredient "cytokinins". When I searched this forum I found this thread:

link

Your explanation gave me a better understanding of the competing hormones. As a result, I wondered if a topical application of hormones, rather than normally occurring hormones administered naturally through the root system, would affect the tree as quickly as is implied in the referenced thread, or if coincidence and timing are more at play.

Barbara

Applied cytokinin, assuming it is absorbed into living tissue, should cause cell division (mitosis) to begin almost immediately. And it would also immediately overwhelm the auxin-based apical dominance. So I would not be surprised at an almost immediate response.

I did notice on the other thread the idea that 6-BAP should be safe for humans since it is very close, chemically, to natural cytokinins. While I don't have any reason to believe that it is not safe, I think that is not valid logic as to why it should be safe -- many of the poisons and carcinogens that affect us do so precisely because they are very close to some natural, normal material in the body, for which they substitute, but once substituted, they don't work quite like the real thing.

Also, the other thread indicated a level of safety because the 6-BAP would not be absorbed into the plant. In order to have an effect, it must be absorbed. So if not absorbed, it won't work; if absorbed, then yes, it is now inside the plant.

I have no reason to think 6-BAP would be in any way harmful, if used on citrus. However, it is not labeled for such use, so I'd not use it. It is labeled for use on apples in Canada, so it must be considered safe for food crops, but I'm not aware that it is used on any food crop in the US. We do allow the Canadian apples to be sold in the US, so in that sense, USDA and EPA must consider it safe.

Hold it at gunpoint until it give in to your demands.

Dr. Manners,

Thank you for the excellent information. My question is if we manipulate the top growth how does that effect root growth? Will it naturally balance? On my new young trees I want the roots to develop quicker than the top. Are there any issues with pushing top growth?