Horridculture – Sealant

P90810++++Grafting compound is a thick sealant applied to a fresh graft union to limit desiccation while the graft knits. A bit more typically gets applied to the cut distal end of the scion. There are various formulations of grafting compound, ranging from something resembling roof patch to a something with the consistency of thick paint.

The stuff, as sloppy and icky as it is, really is helpful. I can not imagine how big orchards were grafted before it was invented.

It is also useful for keeping cane borers out of the cut ends of freshly pruned roses. For those of us who remember how to prune roses properly, leaving only a few thick canes, grafting compound really is practical. I just don’t use it on roses because cane borers are not a problem here.

Since I do not use grafting compound on roses, and the plants that I graft do not need grafting compound, I presently have no use for it. I suppose I could use it on apple and pear trees, but it really is not necessary. When I get around to grafting apricots and peaches, it will only be for a few trees in my own garden, so I will just use candle wax.

This surprises people. At work, I am often asked about ‘painting’ pruning wounds and shiners as trees get pruned, presumably with sealant. Decades ago, it was actually commonly done. Even when I did my internship in arboriculture in 1988, some arborists were applying sealant because it was easier than arguing with their clients about it not being necessary.

The problem with applying sealant to large wounds is that is actually seals moisture within the otherwise exposed wood, and promotes rot. It is best to do nothing, and allow the affected trees to compartmentalize their wounds as they would do naturally if limbs were broken off by the weather. Trees know more about their processes than we do.


Self Grafted Redwoods


Redwoods are some of the most stable trees in the World. That is partly why they can survive for thousands of years. In my entire career, I have seen very few fall, and only inspected two.

Of those two, one fell because it had co-dominant leaders (double trunks) that fell away from each other, which is more of a structural deficiency than instability. The other, which I suspect was demonically possessed, was a small tree less than thirty feet tall, that literally jumped up out of the ground and onto an Astro van more than ten feet away. A rare ‘updraft’ was blamed.

Almost all of the redwoods here regenerated from the stumps and roots of much older trees that were clear cut harvested a century or so ago. Most of those that grew back with structurally deficient co-dominant leaders are very effectively sheltered from wind by their collective groves. Roots systems are very extensive, very resilient, and too intermeshed to be compromised.

The trunks in the picture above are part of a group of several trunks that grew from roots of the same tree that has been gone for a very long time. All are genetically identical and very close together. They happen to be a focal point of a big patio at a conference center. Although the structural integrity of the limbs within their canopy is a concern, the stability of the trunks is not.

Regardless, I am impressed by their attempt to improve stability. The limb that extends horizontally across the middle of this picture from the trunk to the left grafted to the trunk to the right! It is not uncommon for crossing limbs and trunks to rub through their bark to expose the cambium, but how do they stay still long enough to graft together?!

Horridculture – Watersprouts or Suckers?!

90501thumbDo we really know the differences between watersprouts and suckers? It seems simple enough. The definitions of each should be rather distinct.

When I grew citrus, I knew what sort of sucker that I had to contend with. Suckers were any unwanted stem and foliar growth from the understock below the graft union. In the picture of the trunk of the young plum tree above, the graft union is clearly visible between the scion to the upper left and the understock to the lower right. Suckers would be below such a graft union.

This sort of sucker is known as such because it sucks resources that should be directed to the more desirable but often weaker scion. A sucker that is more vigorous than its associated scion is likely to overwhelm and replace it if not removed. Scions are expected on freshly grafted plants, but should become less prevalent as they mature, and the scion dominates the understock.

Suckers might develop either on the short section of understock trunk between the graft union and the ground, or on the roots below the ground. They only need to be below the graft union.

Okay; that definition is simple enough. Here is another.

Watersprouts, as far as I am (still) concerned, are unusually vigorous and typically adventitious stem growth that can resemble suckers, but develops above a graft union. They should likely be removed, but might just be pruned back a bit if they happen to be where a new branch is desired. After all, they are genetically identical to the desired plant, whether it is grafted or not.

Because watersprouts grow above a graft union, they occur only among the branches and main trunks above the ground. They do not grow from the roots of understock below the ground.P90921+++

The picture above shows watersprouts on (VERY badly) pollarded bay trees.

Okay; that is another simple definition.

What about vigorous stems that grow from the roots of ungrafted trees? Can they be suckers if they are not sucking resources from a scion above a graft union? Can they be watersprouts if they are not growing from stems or trunks? It seems that the simple distinction between watersprout and sucker was the location relative to a graft union. What if there is no graft union?!

The vigorous black locust stems in the picture below are growing from the roots of ungrafted black locust trees (which, incidentally, were cut down last winter). Some might say that they are root suckers, which is a third and accurately descriptive designation for such vigorous stem growth. Otherwise, they could be either (or both) suckers or (and) watersprouts. Both work.

I know that many arborists refer to such root suckers from ungrafted trees as watersprouts, which is not at all inaccurate. I am also aware that many arborists refer to watersprouts like those on the bay trees above as suckers, . . . which is sort of inaccurate. I will not argue. I know what they mean.P90921+

Arborists Are Modern Tree Surgeons

90724thumbThe terminology has certainly changed over the years. Not many of us remember what tree surgeons were, or that there were actually a few different kinds of tree surgeons, who performed very distinct tasks. Tree surgeons are now known as ‘arborists’. Much of what they used to do is done by other types of horticultural professionals. The work that arborists still perform is ‘arboriculture’.

Back when orchards were still common in the Santa Clara Valley, Orange County, and many of the areas of California that are now urban, those who pruned deciduous fruit trees while dormant in winter were known as tree surgeons. Of course, they did other work that the trees needed through the rest of the year, and harvested fruit as well. They might be known as orchardists nowadays.

Tree surgeons also assembled new orchards, as well as individual trees in home gardens. It used to be standard procedure to install the understock of fruit trees in the first winter, and let it grow through the following year. A tree surgeon would return while it was dormant the following winter, to graft desired scions onto it. This is now done by nurserymen in nurseries that sell finished trees.

The tree surgeons who we now know as arborists are, of course, still important. The tree surgery that we now know as arboriculture is the sort or work that other horticultural professionals are not qualified or able to perform. It involves the biggest of trees that are out of reach from the ground, or even from ladders. There are still a few different kinds of arborists, but most must climb trees.

Arboriculture is the horticulture of trees. Arborists are therefore horticulturists of trees. Those who are certified with the International Society of Arboriculture, or ISA, have passed an examination of their arboricultural expertise, and maintain their credential by continued involvement with the educational seminars, classes and workshops of the ISA. Arborist can assess the health, stability and structural integrity of trees, and prescribe and supervise necessary corrective arboricultural procedures.

Citrus On The Sucker List

90501thumbA five pound kumquat is a problem! It means something went seriously wrong. Anyone who grew one would concur. They are huge, lumpy, and very insipid, with ridiculously thick pale yellow rind around a small handful of uselessly fibrous pulp. They are protected by dangerously sharp and rigid thorns that can get longer than three inches. Even their irregularly wavy foliage is unappealing.

In reality though, there is no such thing as a five pound kumquat. These huge but useless fruits, as well as the associated thorns and foliage, are those of ‘shaddock’, which is the most common ‘understock’ for almost all grafted dwarf citrus trees. It is what keeps such trees compact, so that they do not get as big as orchard trees. It was there all along, whether we were aware of it or not.

Most citrus trees are composed of two genetically different parts. The understock are the lower parts that develop roots that are unseen underground. The desirable upper parts that produce the familiar citrus fruits grow from ‘scions’ that are grafted onto the understock. Graft unions are just above grade, where the texture of the bark above is slightly different from that of the bark below.

‘Suckers’ are stems that grow from the understock below the graft unions. Because they are genetically identical to the understock rather than the scions, they produce the same fruit and exhibit the same physical characteristics as the understock would if it were growing wild. Suckers can overwhelm desirable scion growth, which is how kumquat trees can produce huge five pound fruits.

Other grafted trees and shrubs, particularly fruit trees, get suckers too. New suckers appear as new spring growth develops. They should be peeled off of the main trunks rather than pruned off. As brutal as this seems, it is more efficient than pruning. Soft young shoots should snap off quite readily. This technique removes more of the callus growth at the bases of the suckers, which could develop more suckers later. Big older suckers should be pruned off as closely and neatly as possible.

Citrus And Avocado From Seed

71227Is it possible to grow citrus from seed? The quick and simple answer to that question is, “Yes.” After all, many cultivars of citrus were originally bred from other cultivars, and then grown from seed. But of course, this an overly simplified answer to an unrealistically simple question about a surprisingly complicated process. Perhaps a better question is “Should citrus be grown from seed?”.

Almost all citrus are grafted for a variety of reasons. Those that are not grafted are grown from cuttings only because they do not need whatever advantages understock (or rootstock) provides for their counterparts. Either way, they are all cloned by some form of vegetative propagation. This ensures that they are all genetically identical to their parents, without potential for genetic variation.

Citrus have been bred and developed so extensively that most types are very genetically variable. Those that are the most variable tend to produce fewer seeds, and might even be classified as seedless. Those with more seeds are probably more genetically stable. Nonetheless, it is impossible to predict if seed grown citrus will resemble their parents, or be something totally different.

Furthermore, citrus are cloned from ‘adult’ growth that is ready to bloom and develop fruit. Those grown from seed start out with vegetative ‘juvenile’ growth that will not bloom. Juvenile growth is typically more vigorous and thornier than adult growth, and possibly wickedly thorny! Some types of citrus outgrow their juvenile phase quite readily, while others may take several years to do so.

Avocado trees grown from seed exhibit some of the same difficulties. Although they lack thorns, they do grow very vigorously and very tall for quite a few years before they bloom. By the time they develop fruit, the fruit could be too high to reach, and quite different from the original.

Just because citrus and avocados can be grown from seed does not mean that they should be. However, different is not necessarily bad. Many seed grown avocado trees get pruned into