Green Thumbs Down...

...to dirty pruning tools.

We urged you to prune last week and will again in this Weekend's Walkabout Webinar: Too Big, Too Much.

Go for it. Prune away!

Please also do this: As you prune keep an eye peeled for diseased wood. If you see anything that looks like tumors or canker - fungus infections that eat away the cambium, enlarging the dead area year by year - be sure to wipe your tools with bleach and water (10% bleach is good), peroxide or rubbing alcohol before you cut again.

A related reminder: Don't prune when wood is wet. Find other things to do on rainy days or when plants are still dripping. Fungal spores and bacteria resting bodies fare much better chances of taking hold and creating a new infection on moist surfaces. They float from already-infected wood and travel on our hands and tools.

Seven son, a monarch magnet, in fragrant bloom each September.

Seven son, a monarch magnet, in fragrant bloom each September.

20 years ago when we first planted seven son, they were indeed problem-free plants.

20 years ago when we first planted seven son, they were indeed problem-free plants.

I am taking this seven son down so it can start over with its gardener watching for infections. The ugly deep cankers shown below almost certainly first infected the limb when it was a barkless young branch.

I am taking this seven son down so it can start over with its gardener watching for infections. The ugly deep cankers shown below almost certainly first infected the limb when it was a barkless young branch.

I am cutting a beautiful 15' seven son shrub (Heptacodium miconioides) to the ground (no worries, it will grow back quickly and even bloom this year). The reason is that the wood was infected by a fungus that the tree cannot seem to encapsulate. So the fungal canker wounds increase in size each year, the branches become weak at that point and die or break.

 Sad to cut a good thing down

Although it keeps growing strong, it is sad to watch its struggle with this as yet unidentified fungus. Every year it loses large branches from its crown. Such a beautiful, strong little tree brought low.

This species is relatively new to cultivation in North America - the first came over about 45 years ago. It came to us, and behaved for years, as a trouble-free plant. Then many of us began to see the cankers. We are seeking identification but so far we are not hearing from pathologists what type of fungus causes the infection or what other plants it might be able to infect.

The tree tries to grow around the infected cambium...

The tree tries to grow around the infected cambium...

...but the fungus grows faster and the canker increases in size each year.

...but the fungus grows faster and the canker increases in size each year.

With such a large dead spot this limb is bound to break.

With such a large dead spot this limb is bound to break.

We left it up for winter. Such pretty white bark! Late into winter it was still moving leaf-made starch down to its roots. Now I cut it back, asking it to put every bit of its stored energy into new canes.

We left it up for winter. Such pretty white bark! Late into winter it was still moving leaf-made starch down to its roots. Now I cut it back, asking it to put every bit of its stored energy into new canes.

Unless the fungus is bound to seven son -- but not many fungi stick with a single host species -- it is likely to be able to infect seven son's close relatives such as honeysuckle and weigela. There are also fungi that can cross plant family lines and we don't know if this is one of them. As a result, we are hedging our bets and cleaning all pruning tools after working on seven son.

Two years ago it lost its first large limb, leaving a gap in its bloomin' crown.

Two years ago it lost its first large limb, leaving a gap in its bloomin' crown.

Here's another suspect branch, from another tree. We have yet to figure what this tree is or what its problem is. (Email us, please, if you have a clue!) You can do the same as we do, that is, when you see suspicious looking wood, take the safe tack. Wipe down our tools after making that cut.