Sunday, June 15, 2014

Buds and Grafting

One esoteric piece of information that helps a fledgeling grafter become more capable is to understand that buds have a robust communication process that can be used to your advantage.

When a bud "pushes" or breaks dormancy the very tip of the extending shoot produces growth regulators, plant hormones, that command neighboring buds to NOT break dormancy.  Pinching out the growing point stops the production of that growth regulator.  One of the most important (and, unfortunately tedious) grafting after-care tasks is to keep stripping off the shoots that grow below the graft.  If left on, those shoots will supress the buds on the graft and it will fail.

Cecil Farris was one of the most proficient grafters I know.  He had unbelievably high percentage of takes on species not generally considered graftable.  He advised me to remove EVERY shoot on the plant except for those pushing from your graft.  I commented, "But that will kill the plant if the graft does not take."  His reply was two-fold:  "The plant knows that.  It will not commit suicide....There is nothing wrong with the craftsmanship of that graft.  There is nothing wrong with that scion.  If every molecule of sugar and protein in that rootstock cannot make that graft work...then I have no use for that rootstock.  It should die."

Nurse buds

Another tip from Cecil was to leave a nurse bud.

Have you ever plunged a knife into your finger and had a dangling flap of skin?  Sometimes the flap of skin bonds back to the meat of the finger and heals.  More often it withers and falls off.  What was the difference?

Many grafts, like whip-and-tongue grafts involve long, tapering cuts.  What keeps the long, thin end of the taper from sloughing off like the flap of skin?

One way is to plan the cuts so that a bud of the rootstock is almost at the very tip of the taper.  That bud will release growth regulators that will scream to the mother plant, "Hey, there is important stuff out here.  Do not abort.  Do not abort."  The mother plant will push nutrients to the very tip of the cut...and thus increase the amount of living, growing tissue pressing against the freshly cut surface of the scion.

Lucky Pittman of Hopkinsville, Ky is something of a legend among his fellow North American Fruit Explorers.  He is very fond of approach grafts.  In an approach graft one cuts about one-third through the branch of the rootstock and binds the scion into the wound.  Much of the rootstock projects beyond the graft and the net result is that the rootstock attempts to heal the wound from both the top and the bottom. The mother plant cannot abort the graft without killing off a substantial portion of itself.

It is necessary to cut off the portion of the rootstock that projects beyond the graft after the wound has s substantially healed or the buds will not push.  But by then, the mother plant will have accepted the scion as part of her own.

Never give up

When you look at  bud you see a simple bump on the stick.  You think it is a (one) bud.  You are wrong. Most of what you see is the primary bud.  That is the bud that is the most differentiated and will push first.  It is also the bud that will make the most demands on the union that might still be early in the healing process.  Most buds also have a secondary bud.  It is usually buried deeply within the primary bud.  In fact, it is buried so deeply that you can rub off the primary bud and the secondary is likely still intact. 

On walnuts, Cecil would would rub off the "big boogers" and leave just the secondaries.  In the case of walnuts there are two distinctly different buds with the secondary the size of the point on a ball-point pen and below the primary.  "Those big bastards will push too soon and dry that scion right out.  You cannot have that.  Just leave the secondarys."

This graft teased me when it pushed a primary bud early on.  The bud grew two inches an then shriveled.  A month went by.  Then these buds on the scion simply exploded.

But that is not all folks.  There are also tertiary buds.  In my mind's eye these are very tiny specks of undifferentiated tissue (the plant equivalent of stem-cell tissue).  They take quite a while to differentiate and become structured tissue that develop into shoots. But they are there.

Do not give up.  Do not give up.  Do not give up.  Plants do not commit suicide.  Do not give up.

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