Everything Is Coming Up Roses

Grafting combines good scions with understock.

When an individual rose shrub blooms with two distinct types of flowers, it seems to be doing a little extra. It provides the big, bold and strongly stemmed roses that it is grown for, along with daintier dark red roses. Eventually though, the small red roses become more abundant, and can crowd out the more desirable roses.

Almost all of the older roses that are grown for cutting are grafted. This means that the stems that provide such excellent flowers above ground are attached to genetically different roots. When such plants were young, the graft union was more obvious, where the canes branched out from the single stem just above the roots.

The stems above the graft union are known as the ‘scion’. The roots below are known as the ‘understock’ or ‘rootstock’. The two are grafted together because the scion blooms so well, and the understock develops stronger and more efficient roots. Scions are not expected to grow roots any more than understock is expected to bloom.

Adventitious stems that develop from the understock below the graft union are known as ‘suckers’, probably because they suck resources that should go the scion. They should be removed as soon as they get noticed, before they can dominate the scion. They become more difficult to remove as they mature.

If possible, fresh new suckers should get broken off from their origin instead of simply pruned away. It sounds violent, but is actually more effective. Stubs left from pruning are much more likely to develop more suckers later. Suckers that get pruned back repeatedly can develop into significant burls.

Old rose shrubs that were planted with an abundance of organic soil amendments tend to sink into the ground as the soil amendments decompose. If a graft union gets buried, it can be difficult to distinguish between suckers and good canes that develop above the graft union.

‘Tree’ roses have two graft unions. The branched scion on top is grafted onto a straight stem of a different variety. The straight stem is grafted onto the understock at ground level. The trendy carpet roses and some other modern roses are not grafted, so will not develop suckers.

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+

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.