Author: Linda Chalker-Scott

Dr. Linda Chalker-Scott has a Ph.D. in Horticulture from Oregon State University and is an ISA certified arborist and an ASCA consulting arborist. She is WSU’s Extension Urban Horticulturist and a Professor in the Department of Horticulture, and holds two affiliate associate professor positions at University of Washington. She conducts research in applied plant and soil sciences, publishing the results in scientific articles and university Extension fact sheets. Linda also is the award-winning author of five books: the horticultural myth-busting The Informed Gardener (2008) and The Informed Gardener Blooms Again (2010) from the University of Washington Press and Sustainable Landscapes and Gardens: Good Science – Practical Application (2009) from GFG Publishing, Inc., and How Plants Work: The Science Behind the Amazing Things Plants Do from Timber Press (2015). Her latest effort is an update of Art Kruckeberg’s Gardening with Native Plants of the Pacific Northwest from UW Press (2019). In 2018 Linda was featured in a video series – The Science of Gardening – produced by The Great Courses. She also is one of the Garden Professors – a group of academic colleagues who educate and entertain through their blog and Facebook pages. Linda’s contribution to gardeners was recognized in 2017 by the Association for Garden Communicators as the first recipient of their Cynthia Westcott Scientific Writing Award. "The Garden Professors" Facebook page - www.facebook.com/TheGardenProfessors "The Garden Professors" Facebook group - www.facebook.com/groups/GardenProfessors Books: http://www.sustainablelandscapesandgardens.com

Update on root-rotted Cornus kousa

A little more than a year ago I posted a Friday quiz based on a failing Cornus kousa.The answer explained that our landscape has, in part, a perched water table that effectively rotted most of the roots of this poor tree over several years.  Last spring we moved it to a different section of our landscape where we know the drainage is better, and I’ve been monitoring its recovery since that time.


Cornus kousa leaves in 2007


Cornus kousa leaves in 2011

We were gratified to see that the leaves this year are significantly larger than those of previous years.  This tells us that root function has resumed, providing enough turgor pressure to expand the leaves to normal size.  It was especially helpful that we had one of the rainiest springs on record.

Take home lesson:  if a tree or shrub is failing in its current location, it’s worth digging up to see what’s going on.  Bad soil conditions?  Move it to a better location.  Bad roots?  Time to hone your root pruning skills.  But wait until fall to do this.  Transplanting this time of year is the most difficult for plants because of the increased water demands of warmer temperatures and expanding leaves.

Quiz answers – more or less

I just got back from a 9 hour overseas flight, just in time to post the answer to last week’s quiz.  So now you know…I wasn’t in the states.  More on that later.

As many of you guessed, this is a fig tree (Ficus spp.) of some sort.  I have horrendous taxonomic abilities anyway, but will cover my ignorance with the excuses that the tree wasn’t in flower, nor were there any signs in any of the little parks identifying the tree.  So we can continue to speculate on what species this is.  I do know it’s quite an old specimen, and that there are some Ficus native to the region, but past that I’m clueless as to whether this really is a native species or not.

And where was this huge tree?  In Alicante, Spain, where I spent a few days visiting my daughter who’s studying there this semester.  (Non-scientific aside:  I would go back there in a heartbeat.  If you are looking for a Mediterranean tourist destination that isn’t overrun with Americans, this is the place to go.)

Finally, these cool wavy woody structures are buttress roots, as Jospeh, Shawn, Rotem and Deb all pointed out.  They have both a structural and storage function: like all woody roots they store carbohydrates, but the over-developed flare helps support the tree in thin soils (like here) or in wet, low-oxygen soils (like those where mangroves grow).  In both cases roots can’t reach far enough below ground to stabilize the trunk, so the buttressing serves that function.

@Rotem also noted that branches can root and support the tree.   While the buttress roots in the original photo arose from root tissue, you can see examples of the rooted branches in the photo above.

And I do love the less-than-serious answers some of you kindly provided for our amusement.  Fred’s "rumble strips for drunks" was particularly apropos, since my last night there was one big street party after Barcelona beat Manchester United in the Champions League soccer match.  My daughter and I ended up in our hotel elevator at 8 am the next morning with a fan with no pants.  We did not ask.

Three part plant quiz

I’m out of town this week, and taking lots of plant pictures.  Here’s an interesting tree, quite common in the city where I’m staying:

Question 1:  What kind of tree is this?  (Genus is good enough – species might be hard to tell.)

Question 2:  In what geographical region might I be staying?  (The tree is native as far as I know.)

Question 3:  What are these woody structures called, and what function do they play?

Answers next week!

Answers to blue flower quiz

Paul, Joseph, Kandi and Derek are all, apparently, Puya fanciers.  But!  It’s not P. alpestris, but P. berteroana – a species whose flowers are more turquoise than sapphire:


Yeah, Kandi, check out those spines!  Even taking pictures is deadly!

And Paul and Joseph were correct – the long green structures are sterile (they bear no flowers) and serve as bird perches.  The nectar almost runs out of these flowers, and as the birds get a sugar fix their heads are covered in pollen.

Thanks to Paul Licht, Berkeley Botanical Garden Director, for my short but fabulous tour that included these beauties.

Exploding watermelons and exploding hysteria

One of our loyal blog readers passed on this interesting article about exploding watermelons in China.  Seems that Chinese farmers have been overapplying a synthetic growth regulator which has led to the of proliferation of plump pepos (gotta love alliteration!).  Of course the media has “blown” this out of proportion with action verbs like “explode” and “erupt”, when what’s actually happening is that the melons are merely splitting. (It’s a pretty boring video if you take time to watch it.)

Ok.  This isn’t to defend the practice of misapplying any chemical.  But the fear generated is obvious in the comments on this video – just scroll through them.  The growth regulator in question is forchlorfenuron – a cytokinin legal in the United States and approved for use in very low concentrations on kiwifruit and grapes to enhance fruit size, fruit set, and cluster weight. It’s been approved for use in the US since 2004 and has been tested extensively prior to that approval for human and environmental safety.

Fruit split happens all the time during ripening. I’m sure most of you have seen this yourself, like when your tomatoes are overirrigated or cherries get unseasonal rain. And it can happen when growth regulators – natural or synthetic – are misapplied. But the fruit isn’t dangerous.  It just looks bad, and might not taste that great, either.

There are lots of things to worry about out there.  But growth regulators used in fruit production really aren’t one of them.

A rant about urban farming

(I know this one will get me into trouble…but hey, if I don’t tick someone off I’m not doing my job.)

I have mixed feelings about the increased popularity of urban farming. On one hand, I love the idea that people are becoming more involved in producing their own food. But on the other hand, the naivety of many urban farmers is scary – because they assume that home-grown food is safer and/or healthier than what they can buy at the market.

I give a lot of seminars every year, on a lot of different topics. At the end I usually have a room full of happy people, asking lots of questions and eager to go apply the new knowledge that they’ve gained. But one talk I’ve done has exactly the opposite effect. It’s the seminar I give on vegetable gardens and heavy metal contamination of urban soils. The audiences are subdued and worried. It doesn’t make me feel very good, but on the other hand I know I’ve got people thinking.

Heavy metal contamination of soils is insidious.  Like the iocane powder in The Princess Bride, these compounds can be odorless and tasteless…and deadly. Lead, arsenic, cadmium, and a handful of other heavy metals are the legacy of centuries of “civilized” living. Mining, smelting, manufacturing, and driving all contribute to localized toxic hot spots. Unlike organic contaminants, heavy metals are elemental. They don’t break down and go away. The lead from gasoline fumes of the past is still found along roadsides; the arsenic from early pesticides still lingers in soil used for field and orchard crops. Many plants not only take up heavy metals, but accumulate them in their tissues.

It’s easy to avoid heavy metal problems: soil tests are the logical first step. If soils are contaminated, you can build raised beds or use containers with clean, imported topsoil or other growing media for vegetable gardens. Likewise, you might want to take care in buying produce from farmer’s markets – ask questions about possible soil contamination.

So by all means, grow your own vegetables – save money and take satisfaction in producing your own food. But be careful out there.

Solution to Friday’s flower fuddlement

Ed and Gayle correctly pointed out that short day plants (those that bloom in the spring or the fall) can sometimes do both.  The asters probably experienced some transplant shock in the fall, which would have suspended floral bud development.  This phenomenon could also be due to mild winter conditions (as Ed and Gayle also mentioned), which could have spared flower buds normally killed by freezing temperatures.

In any case, as spring daylengths approached those found in the fall, flower development continued and voila!  Asters in the spring!  Likewise, there are a number of spring bloomers that sometimes have a second (usually reduced) floral display in the fall.

Thanks again to Ginny for sharing her photographs and information!

Floral fuddlement

Gardeners love asters as part of their autumn floral palette.  Yet these native asters are blooming now – in the spring!

These specimens were purchased last summer and planted in the fall in Florida. Why might they be blooming out of season?

Reader Ginny Stibolt contributed today’s puzzle.  If you’d like to be a guest inquisitor on our blog, send photos and explanatory text to Linda Chalker-Scott.

Mystery sparkler exposed

I really liked the answers you brave few came up with for Friday’s photo.  I could absolutely see how each one made sense – but unfortunately none of them were correct.  It’s actually a raindrop sitting on top of an expanding larch bud:

This turned out to be much trickier than I anticipated.  I promise the next one won’t be.

(And no, the raindrops do not magnify sunlight and cause the expanding needles to burn!)