Merits of topping rootstock

[Dale B.]

I am looking for the best way to increase the root mass and caliper of rootstock. It has been suggested to me that topping rootstock will induce branching which will increase trunk caliper and root growth faster than leaving the long branchless central leader.

I have thought about topping them to 12” when I pot them into 4” pots near the end of their first winter. Does anyone have any words of wisdom on the merits of topping rootstock to grow more roots?

[Elmore]

not much here but topping them certainly cuts down on them falling over and drooping. If you can root them it would be cost effective and if you had too many I could house them over here. Brad.

[mr.shep]

Hi Dale:

Personally, if your seedling Maples are over 12" tall I would have them
in one gallons rather than 4" pots. If your Maples are that tall already
then the roots should already be close to filling out the 4" pot. Are your
seedlings grown indoors, in a greenhouse or grown outdoors? I am
assuming they are in a greenhouse.

Years ago, the psychology of a tree told us that if we topped a tree we
would initiate a response to the root system. We were advised that if
we wanted to ensure root growth that it was advisable for us to top our
trees. For many trees topping the tree will signal the plant to alter its
current physiochemical processes in order to initiate a growth response
to the root system. To a plant psychologist it is the trees way of protecting
itself and to better ensure its survival. There are some detractors that say
topping a tree will not promote root growth but I have personally seen
enough results to support the contrary instead.

As far as increasing the caliper of your seedlings, I have to ask myself
how large a caliper do you want for grafting? I've seen seedling Maples
have their tops cut off grown in the ground just so the calipers would
increase in size in advance for grafting during the Winter. I've also seen
the tops broken, not snapped off but left hanging (severely bent is a better
word for it) on the plant about 4" from the top, used for both Maples and
Citrus seedlings several months prior to them being ready for grafting.
The broken top method was also used soon after the seedlings were
grafted also.

A lot depends on how much size of caliper do want in your seedlings
and when you want them ready to graft or to bud onto them.

Jim

[Dale B.]

Normally my rootstock seedlings spend the first year in 606 inserts, 36 cells per flat. If I buy them, they are in Jiffy pots about the same size. They are usually 24” to 32” tall by their first fall and no branching. I pot them into 4” pots, 18 to a flat, in February and put them into a green house to give them a head start and protect against late freezes. They are moved outside by the end of April. I start grafting in mid June.

I leave the new grafts in the 4” pots until the following spring when they are moved to gallon containers. I find that grafting is easer if the rootstock is in 4” pots. I tend to graft higher if the rootstock is in larger containers. I have to keep telling myself to graft lower. I do move to gallons if I am grafting high on standards so that the pots don’t fall over due to the weight being so high.

Some of the reason that I keep the rootstock and new grafts in 4” pots is weight and space. Moving a thousand or two maples in and out of a green house is much easer if they are 18 to a tray than one to a gallon. They are also easier to ship if they are in smaller pots.

The rational that I was given to top the rootstock was that it will encourage branching and that two or four branches will put out more leaves than one leader. The total leaf area is the driving force for the root area required or produced by the plant. The trunk caliper is an indicator of the root mass of the plant. – I don’t know if this line of thinking is correct? I have bought rootstock in the past that had been topped and it grew very well, but I didn’t have a control for comparison. I didn’t think of it while I was potting purchased rootstock this past winter and I don’t want to top them now and waste the output of this spring’s growth.

My goal is to maximize the root mass available for the new graft to help it on its way.

Thanks,

Dale

[mr.shep]

Hi Dale:

Thank you for your clarification.

Technically, the size of the caliper does not reflect the total mass of the
root system. I know people that do wish it were true though. From my
view the weakest area we have in Maples is not having vigorous enough
root stock to start with. I could be wrong but I have not seen many real
attempts to develop a strong, sturdy enough root system starting from the
seedlings. To me, the Achilles heel for Japanese Maples has always been
the root system.

Most of the time the growers I know either grow their own seedlings or
buy them in liners to grow on themselves. Also, the growers I have talked
to did not want a large caliper but a caliper close in size to the wood they
would be using for grafting.

Most of the people I know would graft in late November to January but I
know of some people that will start grafting again in May through June
also. I know of a grower in Oregon that buys his root stock just before
he does his grafting in December. He does not want to grow his seedlings
on as he feels he is limited for space and to some extent he is right.

The purpose for bending the top was so that no side shoots would develop.
The thinking was that if the top was left on as opposed to cutting it off that
the plant would initiate a plant hormone to activate root growth without
producing side shoots from the top. The scientific community may have
some doubts about the merits of bending the top but some of the growers
I know swear by it. It seemed more important to them to bend the top over
soon after the grafting had been completed. The thinking there was that
since the plant still had some apical dominance in tact by virtue of the top
not being completely cut off that the wound where the graft took place
would heal faster. The faster the healing, the likelihood that the grafted
areas would also heal over quicker and that those growers felt they had a
higher percentage of successful graft takes because of it. Based on their
numbers of successful grafts I am not going to say they were wrong.

You have to do what works best for you. As long as you are content with
how things have turned out, it makes little difference what anyone else may
think.

Best regards,

Jim