There may be some misunderstanding of what is actually going on here. In a citrus tree, xylem sap flows throughout the day, but stops (or nearly stops) at night, year-round. Xylem sap is the water supply coming up from the roots, carrying fertilizer nutrients with it. Phloem sap, on the other hand, moves more or less continuously in the tree, carrying sugars, amino acids, hormones, and other plant metabolic products around. There is nothing that happens at any time of year in a citrus tree that would be analogous to the "sap flow" in something like a sugar maple tree, in which massive amounts of stored starch in the roots are converted to sugars and transported upward for use by the spring growth flush.

Some methods of grafting work about as well on any day of the year -- chip budding and cleft grafting, for example.

However, there are grafting methods that rely on the bark of the rootstock plant "slipping," meaning that it peels cleanly away from the wood (T-budding especially, the most popular of all methods of propagating citrus). In this case, there are definite "good" and "not so good" times to do the operation, and in that case, it generally happens when the tree is in a major flush of new growth. It's not really related to "sap;" rather, it is the fact that the vascular cambium, which is a very thin layer of cells between the bark (phloem) and wood (xylem) is actively dividing new cells, in the process of making new wood and bark, as the stem thickens during the growth flush. Those new cells are softer and not as tightly "glued" to their neighbors, and so when you cut into the bark and pry it back, the bark "slips" as the cambium layer tears. Growth of the vascular cambium is stimulated by auxin hormone (3-indoleacetic acid) flowing downward from the new growth, through particular cells in the phloem tissue. So it occurs in a wave, somewhat later than the beginning of the top flush, and ending just after the end of the top flush. It's easy to test for -- you simply try to cut and peel a bit of bark. Either it will peel as easily as a ripe banana, or it will hang on tightly and you'll just be scraping splinters.

Malcolm

Malcolm M. Manners, Ph.D.
John and Ruth Tyndall Professor of Citrus Science
Florida Southern College
Lakeland

Oh my! Thanks for the detailed information!

Malcolm, your explanation of 'sap flowing' and 'bark slipping' is very valuable to me. It explains why my cleft grafts are more successful than my T-budding.

How does one encourage sap flow, or new growth, in rootstock so that budding is more successful?

John

John, You can just wait until the tree naturally flushes. But in a commercial nursery situation, they tend to carefully give entire blocks of seedlings the same care -- same fertilizing schedule, same irrigation, same environmental conditions in the greenhouse, etc., and that tends to synchronize their growth. Even then, there will be a percentage of the seedlings that are not in synchrony, and so they are either set aside, or more often, chip budded (which does not require slipping bark, but does take a bit longer to do)

Interesting. Is it true that one must graft mostly in Spring?

Commercial nurseries graft (T-bud and chip bud) year-round. But the easiest time (the time when a beginner may expect the highest rate of success) may be in the spring, when the seedlings are making massive new growth. Certainly very hot or very cold weather could reduce your probability of success.

Thank you so much for your guidance . I am from Cape Town, South Africa and a beginner. Spring is hot in South Africa.

Perhaps late winter then -- as soon as you can get your rootstock seedlings into rapid, strong new growth.

Good info here MM on plant biology and how it changes over the season.

Malcolm! Are you back? So good to hear your responses!

I can't always graft when bark 'slips'. I have torn up more bark trying. Lately I have preferred veneer grafts and chip bud grafts, which are successful for me. Dont' have to peel bark for those.

I have grafted in winter in my coolish garage.. I didn't think they took, but they stayed green and finally flushed out in late Spring. Summer grafting is quicker in my region.

Dave, I didn't really go anywhere, but tend not to actively follow this group. But when someone comments on a thread I've previously commented on, I get a notification. So that's why/how I saw this. M

What’s wrong with this group, we are trying like any other group to get better. I personally like a different kind of set up. I remember your name from way back but switch to citrus a few years ago. Anyway a little help now and than would really nice.

There is a lot of interest in citrus from people in zone 8 and lower, me included. There are a lot more ladies that like help from professionals like you.

Bob I agree with you! Wished you were around more Malcolm! I just basically grafted a t bud graft yesterday and it the rootsrock just finished flushing not a major one Of course but the bark did peel back with some effort. hope it’s ok!

I really appreciate his guidance. I am about to order budwoods to graft citrus fruit salad tree. Dr Manners, what do I need to know before I graft this fruit salad tree. What is the advantages and disadvantages?

There are two potential problems with a "fruit salad" tree:

1. Invariably, the different varieties don't grow at the same speed or shape, so there will always be one trying to shade out and take over the other varieties. So you have to do frequent, selective pruning to keep the tree more or less balanced. I grew up with a grapefruit/key lime tree, and it was a major hassle there, in that the grapefruit portion grew at more than twice the speed of the lime.

2. Depending on your source of budwood, one of the varieties may be carrying a virus disease to which it is tolerant, but to which one of your other varieties may be susceptible. This is particularly true if you get one with citrus tristeza virus -- in that case, it's important that the rootstock and all of the other scion variety combinations are tolerant to that disease.

Thank you for your guidance . I willing to prune my "fruit salad" tree to balance it . I am buying budwood from the Research Institute that sells disease free budwood here in South Africa.

Dr manners always a wealth of information! :) thank you for sharing! I have such a tree and I will definitely prune it to keep things balanced.