Friday, April 28, 2017

Brian Humphrey on Maple Propagation

Brian Humphrey from England, a well-known plantsman/nurseryman – and seldom is one man both – is writing a book on propagation. He asked me to look at the maple grafting part in case I “see any mistakes which should be corrected.” The twenty pages I reviewed couldn’t have “mistakes” because it was merely discussing various methods and observations about maple propagation – and there really isn’t a right or wrong way. I did learn a few things and got some ideas to try at my nursery, and it wasn’t the first time that Brian has shared his plant knowledge with me.

The following is my response to some of the topics that he brings up, but I won’t take the liberty to reveal his part – you’ll have to buy the book yourself.

Acer x 'Purple Haze'

You mention the “remarkable” hybrid A. x ‘Purple Haze’. It arose in an outdoor seed bed of Acer griseum, and was noted for larger leaves with purple undersides. I sent plants to Europe 12-15 years ago, to Cor Van Gelderen and maybe others, and I was trying to receive confirmation that it really was a hybrid. I was hoping that “science” would look at it and make an official determination. I heard nothing further until the Maple Society Convention in Belgium in 2011. Generally half the attendees at these events are botanists, and the other half are simple rustics such as myself. I have witnessed that most of the academics defer to Piet de Jong, that he is considered the highest authority on Acer. He smugly claimed that that the hybrid was “impossible,” that ‘Purple Haze’ was simply a variation within A. pseudoplatanus. Interestingly the griseum-appearing leaf colors a fantastic orange-red in autumn, and I’ve never seen an A. pseudoplatanus do that.

Acer x 'Sugarflake'

Acer x 'Cinnamon Flake'

More ornamentally worthy than ‘Purple Haze’ is Acer x ‘Sugarflake’ and if it’s a hybrid (saccharum x griseum) then it is another cross between different sections. De Jong also dismissed that as a hybrid, and was certain that it was just a variation of Sugar maple. Of course he has never seen a ‘Sugarflake’ specimen, and I wonder what he would make of the (somewhat) exfoliating trunk which reminds me of x ‘Cinnamon Flake’ (griseum x maximowiczianum).

Thirty years ago seedling availability of Acer griseum was rare, so I propagated the paperbark onto Acer rubrum. One of the original grafts still grows in front of the house of the late Dr. Corbin of Portland, Oregon. The union is still smooth and the top and bottom were the same size the last time I saw it, but of course of very different color. Occasionally a rubrum sucker will try to form, and the family has been instructed to rub them off when small.

Acer griseum 'Narrow Form'

I once had a seedling of A. griseum that was notably narrow, and I thought that if we propagated it would make a perfect street tree. When my specimen was about 15’ tall, a customer – and now I can’t even remember who it was – begged and begged to buy it. I didn’t want to sell it but eventually I relented. Before shipping I harvested a few apical scions and grafted them on the only rootstock I had – Acer rubrum. A few grafts took and all of them have proceeded to grow as regular griseums, and none of them exhibit the narrow form. If you look at Buchholz introductions on our website you’ll notice Acer griseum ‘Narrow Form’. I don’t propagate it at all anymore because its not at all narrow.

Acer nipponicum

I have grown a few Acer nipponicum, but always as seedlings. I once asked Peter Gregory if he knows of a suitable rootstock and he suggested that I try Acer pseudoplatanus “because it accepts almost everything.” My grafting resulted in 100%... failure, and I have never wasted my time again.


Acer pentaphyllum

I notice that the suggested rootstock in Cor Van Gelderen’s table for Acer pentaphyllum is Acer pseudoplatanus. I have never tried that because I achieve good success with Acer rubrum.

Acer buergerianum 'Angyo Weeping'
Acer campestre 'Carnival'

Acer circinatum 'Baby Buttons'
Acer shirasawanum 'Moonrise'

In the section on Summer Grafting – “Some recommend that for species other than A. palmatum summer grafting should be delayed until September.” I don’t know why to wait if the wood looks ready. Last August we had success with Acer buergerianum, campestre, circinatum, conspicuum, japonicum, macrophyllum, palmatum, pentaphyllum, pictum, shirasawanum and sieboldianum. Admittedly the x conspicuum ‘Phoenix’ grafts were only about 50%. It was our best year ever and my propagator will be getting a raise. Of course I know that next year could be our worst ever, and I’m sure no one will want to return the extra money. The point is that you can have good success with various species without “waiting until September.”

My success rates with grafting in October is that the earlier the better. I think I it is probably weather related, with some Oregon Octobers being cold and gloomy and others being warm and sunny. We really like to finish by mid-September. I was surprised to see Vergeldt in Holland grafting on October 20 one year. He used low plastic tubes with bottom heat and kept the grafts dripping with sweat. The rootstocks were pruned harshly with no foliage remaining, so there was no chance of them catching mildew or other disease. After 20 days, the grafts were uncovered and Vergeldt’s son implied that they would have good success, of course depending somewhat on the cultivar used. Two days later I flew home and copied the Dutch method as best as I could, but my results were poor. I couldn’t duplicate the feel of a Dutchman’s greenhouse – my humidity and light are so different in Oregon.

Saya deleafing scions

I prefer to deleaf all scions – it just keeps the operation cleaner. I have experimented with keeping leaves on and that works as well, but it puts me in a bad mood to walk past a withered moldy mess. Besides I have grown closer to my youngest (now 11) daughter when we deleaf scions in the evening after dinner. She is fast!

Acer palmatum 'Japanese Princess'

Acer palmatum 'Ikandi'

We had some empty spaces on our hot pipe after grafting Fagus, Quercus, and other species. We had about 200 rootstocks from failed summer grafts and on Feb. 20 I cut scions of Acer palmatum ‘Japanese Princess’ ‘Ikandi’ ‘Alpine Sunrise’ and the new ‘Bloody Talons’. All scions came from stock in the greenhouse and on Feb. 20 they were just beginning to swell. They were kept on the hot pipe for 20 days and now, two months later, we see that nearly everything is vigorously growing. I have had the opposite results before too. We keep our rootstocks in their pots and do no “drying off.” We don’t dry off our summer rootstocks either. What I don’t like about the hot pipe – we call callus tube – is that we must graft about 3” above on the trunk so that the union is at the heat source, when I would much prefer to have my grafts as close to the soil as possible.

I have “stick-budded” before, but I don’t like it because the scion-rootstock size disparity means that I have to keep the plant for an extra year or two before the cultivar catches up, so they are not suitable to sell as one-year grafts. Years ago a Chinese woman competitor propagated all of her maples via stick bud. Her product looked wimpy and vulnerable compared to a normal side graft and I took a lot of her business away.

On the other hand my sister lived in the woods near the Oregon coast, and Acer circinatum grew wild just past her lawn. For fun I stick budded a couple dozen red laceleafs on her vines and some actually took. They were never very vigorous because she didn’t top the circinatum rootstock; nevertheless it was an odd sight to see red in her green jungle.

Acer circinatum 'Little Gem'

Juniperus squamata 'Blue Star'

I was surprised to see the mention of A. circinatum ‘Little Gem’ as a candidate for top grafting. If palmatum rootstock is used the vine cultivar – whether a witch’s broom or an upright grower – will outgrow the rootstock and the product will always need the support of a strong stake. I find this also true with palmatum cultivars that originate from brooms such as ‘Shaina’ or ‘Kandy Kitchen’. Other dwarves or spreader palmatum cultivars such as ‘Little Princess’ or ‘Japanese Princess’ seem to be ok top worked, although stem colors seldom match. Whether with conifers or maples, as well as with other plants, what happens to the rootstock of a top graft can vary greatly. Some stay skinny forever and some expand significantly. If you graft a Juniperus squamata ‘Blue Star’ (witch’s-broom origin) atop a J. scopulorum ‘Skyrocket’ the ‘Blue Star’ seems to act as a bottle stopper and the stem fattens up nicely. Abies koreana ‘Ice Breaker’ works but Abies koreana ‘Blauer Eskimo’ does not. I suppose the species of rootstock in question is a factor too.

Years ago the propagator at Monrovia Nursey wanted to visit because he had heard that Buchholz did well with maples. I didn’t keep anything secret from this southern California university graduate of horticultural science. A week later I requested a visit to their propagation department and after a lot of hemming and hawing from the Higher Ups, I was finally granted permission. Boy, did we do things differently! Their rootstocks were about 2/16-3/16” caliper growing in 2” by 2.5” deep “rose pots.” I wondered how often they would need water on a hot day. Their crew performed side veneer grafts with leaves still on the rootstocks, so the scions started out in a good deal of shade. The propagator admitted that they had to frequently reduce the top foliage which was a very labor-intensive task. By contrast we use 3 9/16” pots with a rootstock caliper of about ¼”. Our container’s volume is about 8 times larger that Monrovia’s and of course they take up more room in the greenhouse but at least we don’t have to constantly prune.

Monrovia had already finished a few thousand grafts, and I was shocked to see their full-time watering man with a small wand and with very low water pressure going up and down the pots. Each pot would be covered at least ten times before it was sufficiently wet, and great care was taken that no water ever touched the grafted union. They kept up this practice for about two months before the grafts were deemed safe for overhead water. What a boring job their hand-watering must have been, and I think that the irrigator was a university graduate too.

At Buchholz Nursey we care less about the ingress of water into the graft, and sometimes our overhead is turned on one day after the graft was made. However we use large 8 x 3/8 x 0.20 budding stripes and begin wrapping ¼” above the graft union and end ¼” below. We leave no gaps in the budding strip, nor do we seal the top. This method works for maples and conifers, and because it does we’ve never experimented with any other way, although I am aware that many nurseries in Europe and America secure their grafts differently.

Total removal of rootstock in April

We head back the rootstock on our summer grafts at least once, and perhaps twice for those grafted earliest. In the spring, (about the first of April in the greenhouse) when the scions show a couple of inches of new growth the rootstock is completely removed, leaving one bud set on the rootstock above the graft.

Considering using 2-year scionwood – and larger scions – it is not a practice at Buchholz Nursey unless the 2-year wood is the only type available and large enough. But I have seen obscenely large 2 or 3-year scions used in England (Peter Catt) with apparent success. I understand one of the goals of horticulture is to “improve” on nature and to speed her up so that we can sell the product more quickly. I probably will experiment this summer with larger scions, but I wonder if my graft percentage will go down.

I know that Vertrees recommended drying off rootstocks (1978) at least with A. palmatum. My first years I did as told, but eventually I stopped because I couldn’t see the value in it, and actually there seemed some danger in the endeavor to adequately rewet the pots. Always keep in mind that the solo propagator has the freedom to experiment and follow his inclinations; those with employees inevitably compromise and often adopt practices where the employees will do the least amount of harm.

We overwinter summer grafts in frost-free greenhouses, but some experimenting on temperature lows might be interesting. 15 years ago we had 18,000 laceleaf and ‘Bloodgood’ grafts in a greenhouse that collapsed under heavy snow. It was a custom-graft project where the customer owned all the rootstocks and provided all of the scions. Throughout the night the grafts were exposed to 3-5 degrees of frost, then early in the morning the plants were transferred to an above-freezing greenhouse. We threw out 168 plants that were broken at the graft, but everything else looked ok. That spring we were pleased with our normal 90-something percent success rate, and I was glad that I never bothered the customer (Ekstrom Nursery) about the incident.

1 gallon Buchholz maple

Competing nurseries usually pot up their one-year grafts into 1-gallon pots one year after grafting. They are watered and fertilized heavily and kept in warm poly houses. They are staked onto bamboo where some whips achieve 3’ of growth. The following spring they are shipped to garden centers as a plant slightly less than two years old. At Buchholz Nursery we don’t stake *Acer palmatum cultivars – we prune instead – and keep them an extra year. Our 1-gallon pots are more husky with greater caliper. These days the competition charges between $10-12 for their one gallon pots; we charge between $14-16 for ours. Admittedly their system is more profitable, but I am more proud of my plants. Furthermore, when growing the gallons on to larger sizes, our future plants will have more impressive shapes than the pushed-whip method.

Acer palmatum 'Ryu sei'

*An exception would be A. p. ‘Ryu sei’ where we want height first. When they are as tall as we want, then they are topped to form a well-branched umbrella shape.

One of the best aspects of horticulture is that you can rub shoulders with some of the greatest plantspeople and learn from their experience. There have also been times when dumbshits teach me a thing or two. I don’t know where I fall that continuum, but at least I’ve been able to make a living.


  1. urple haze in UE is named griseumxpseudoplatanus?

  2. Amazing blog, I've just discovered yours by googling 'Nelis Kools' :).

    I'm into Acer and Giant sequoia, but my success into propagating Acer has been so far close to nonexistent.