Garden School:

Garden School:
Teaching this week: Rose pruning (as always!) and water management

Friday, 15 April 2016

Reverted Salix caprea 'Kilmarnock'

A few days ago, I wrote yet another article about these small, weeping trees, featuring questions from two readers, each wanting information about their pruning and management.

Brenda in Georgia has kindly sent me photos of her two "problem" trees, which is fantastic, as now I can make comments that really make sense!

The first thing to say is that I hadn't realised that these were very short trees: I had assumed that they were the "usual"  Kilmarnock type, where the weeping part is grafted onto a short, upright stem of about 5' tall.

However, in this case they were both grafted just a couple of inches above the ground. It doesn't change what they are, or how to deal with them, but it does result in a rather strange-looking "tree". (Sorry, Brenda!)

Starting with the upright one, I'm afraid it does look like a reverted tree: if you look really closely at the base, just above the ground, you can see there is a bulgy section - that's the graft.

I've made an annotated enlargement of the bottom of the stem, to show you what I mean, but first let's quickly run through an explanation of grafted trees.

A nursery worker starts with a small, ordinary, upright tree - in this case probably a normal, non-weeping Salix caprea (Grey Willow). It will have a single, strongly upright central trunk, and it will be good and healthy.

This is called the “rootstock”.  This is chopped off at the required height - normally, about 5' high, but in this case just a couple of inches above ground level. They then take some cuttings of a different plant, a pendulous Salix caprea, and graft them onto the top edge of the rootstock. Usually, there will be a number of cuttings grafted onto one rootstock, in order to get a regular spread of branches: sometimes only one, depending on what was required.

The grafting involves cutting slits in the bark and gently sliding the cuttings into place, then binding them all with grafting tape. If the work is successful, the cuttings will “take”, and will start growing. The rootstock makes a callus over the grafts: in effect, it “heals” over them, and leaves a visible bulge. This is how we know when a tree has been grafted.

So we have a grafted tree with a visible bulge: below the bulge is the rootstock, above the bulge is the decorative, grafted material.

Now, if you have read any of the other articles, you will remember that I mention reverting as a problem with grafted trees - this is where the rootstock sends out growth, which is usually more vigorous than the decorative top section. If the owner doesn't notice in time, these shoots can take over the entire tree - all the energy of the rootstock goes into supplying its own shoot, and the grafted section is left to die.

In this photo, below, I have drawn a sketch with arrows, and the blue line indicates where the graft is.

If you look at the graft area, in the photo above, can you see that there is a dead, rotting stem pointing straight up, and the strong live one is coming off at an angle? From a distance, it looks like an upright stem, but you can see at the very base that originally it was shooting out at an angle. This is very typical of a grafted tree where the top part has failed, and the rootstock has taken over.

If you check between the picture and the sketch, you can see:

A is the rotting remains of the original, grafted top, you can see that it is above the graft line.

B is the new shoot - and can you see where it originates from? Above the graft line, or below it? Yes, it's below.

C is the point on the rootstock where that shoot originates from.

This means that this particular tree has sent up a shoot from below the graft union, which has taken off like a rocket, and is now starting to grow into a perfectly ordinary, non-weeping, willow tree. The bad news for Brenda is that it will grow and grow, until it becomes a full-size willow tree, which is way out of proportion for her lovely garden.

The only course of action here is to dig the poor thing out, and throw it away - it's not even worth planting out somewhere where it can be allowed to grow to fulfilment: that rotted stem is eventually going to spread disease back down through the rootstock, and it will die long before maturity.

Now we turn to the other one: how did you describe it, Brenda? "A tangled mess" was the phrase, I believe! *laughs*

Here, it looks as though the idea was to have the willow tumbling down over the low wall.

However, it's very congested, you can't really see the structure of it, and the ground around it is so cluttered that it just looks a mess.

This next part is a bit tricky, as I have to try not to insult Brenda too badly (!!) so what shall I say? If I were your gardener, Brenda, I would certainly attempt to retrieve it - but it's one of those jobs that is much easier to demonstrate than to describe, so you might not want to do this yourself - although I would certainly encourage you to have a go, on the grounds of "you have nothing to lose!"

I would do exactly what I said in the article about pruning a weeping tree, except that I would be on my hands and knees while I did it.

Firstly I would snip out any dead stems: at this time of year, that means anything which is not putting forth leaves. Then I would snip out,  as close to the trunk as I could manage, some of the lowest stems, the ones that are brushing the ground. Then I would look at what was left, and would consider a little artistic fettling, to take out any branches that were crossing other branches, or which were spoiling the general appearance of the - er - tree. Although I'd probably have to call it a shrub, now that I can see how small it is!

After doing all that, I would clear out all the fallen leaves and debris underneath, and would clean out any weeds or other plants growing under the canopy. I'd probably also spread a thick mulch of something really dark in colour, such as bark chips, in order to show off the plant.

Now, what would I do if it were mine?  (I can feel Brenda wincing in advance!)  Well,  I would dig the whole thing up and put it in a pot, frankly: on a raised stand, so that the branches could "weep" properly, and I would probably mulch the pot with light-coloured gravel or shingle - again, for contrast, so that you can see the shape of the branches in winter.

So there you go - I hope this tailored advice and encouragement is what you wanted to hear, Brenda, and that's my advice: dig out and dump the tall one, and be brave, and have a go at the short one!

Wednesday, 13 April 2016

How to cut a Box ball

I love topiary, and I get great pleasure from the twice-yearly (or more!) pruning - it's so nice to be presented with something fluffy, and to turn it back into something crisp, compact and neat.

However, many people struggle to clip them, and I am always being asked how I do it: like much of gardening, it's easier to demonstrate than to describe, but today, with the help of a lot of photos, I am going to try to show you how to clip small box balls.

 First step, start to cut a channel up, over, and down, circumnavigating your ball, from pole to pole, as it were.

It doesn't matter whereabouts you do this first cut, just do it wherever it is comfortable for you to get to it.

As you can see, I am reducing this rather fluffy ball by a couple of inches.
Step 2: the first cut is done, all the way up, over and down.

If your balls were pretty much the right shape to start with, all you have to do is cut a constant amount off: just follow the existing shape, and all will be well.

The only "trick" with balls is to ensure that you keep the "bulge" or roundness - don't ever clip "downwards", always go outwards.
 Step 3: make another line of clipping, from the north pole round to the south.
 Step 4, predictably, is to complete step 3 all the way over and down.

Now you have an outline to aim for.

Step 5, cut the first quarter.

By cutting pole-to-pole channels first, you can see roughly where you need to go, and it prevents you starting at one point, going all the way round and then finding out that you are not in line with where you started, which can be disastrous.

Step 6, clip the next quadrant.

At this point, I am clipping fairly closely, but not obsessing about getting it perfectly smooth or perfectly even: these cuts are all about getting the general shape, size and proportion correct.

Step 7,  third quadrant done.

Step 8, all four sections have been done.

Now is the time go back and even out any lumps and bumps.

Stage 9,  there, much better. Looking at this photo, I can see a couple of slight angles which need a little smoothing over, and it is always worth gently fluffing it up with a hand, to shake loose all the clipped leaves, and to find any odd uncut stems that would otherwise pop out as soon as you walk away, spoiling the effect.
There is no need to get it absolutely 100% perfect - as soon as you step away from it - right - it suddenly looks completely wonderful.

And of course, within a week it will have a batch of new leaves, which will hide any discrepancies and will quickly fill any small gaps.

Having finished the clip, it's important to clear up all the debris, shaking the hedge gently to get out the loose material, and scraping it all away from underneath both the hedge and the ball.

This is to help prevent box blight and other assorted diseases: closely clipped hedges are often susceptible to disease, as there isn't much air circulation within them. You can help prevent these problems, by always clearing debris away when you clip, and by keeping the root area clear, so that air can get in.

The final job, after clearing away the mess, is to give the topiary a good watering, and a balanced liquid feed, as the pruning will prompt it to produce a new flush of leaves to replace the ones I have just cruelly removed, so the least we can do is to give it some encouragement.

Monday, 11 April 2016

Salix caprea Kilmarnock - more questions!

I've written several articles in the past about this small tree, which is extremely popular in smaller gardens: if you look at the top left of the screen, you will see an orange blob and, next to it, an empty box with a magnifying glass icon in it. This is the Blogger "search" button, and if you type Kilmarnock into it, it will pull up a list of all of them.

Back in July 2014 I told the story of how I'd spotted a very neglected Salix caprea 'Kilmarnock' on a local industrial estate, and had done some sneaky guerilla gardening to rescue it.

Well, not really "guerilla" gardening, I spoke to the groundsman and obtained permission to do it, but it sounds impressive, and oh-so-trendy, to call it guerilla gardening... anyway, the tree was rescued from total reversion, and made an excellent recovery.

Then a couple of people asked me for more detail about the pruning,  so I wrote another article about Pruning of Small Weeping Trees, which covered Weeping Pear, as well as our Kilmarnock.

In addition, there was a question about growing a weeping Kilmarnock from seed, which is unfortunately not possible, as I explained in this post.

Today, there are two questions in my inbox, both about pruning, so let's talk about Kilmarnocks again!

The second question - dealing with the easier enquiry first! - is from Richard ("Hi, Richard!") who asked why I cut below a twig that's pointing up and out, with a side order of "do you cut at the node?"

The reason for cutting below an upward-springing twig is to preserve the waterfall shape - if you cut just below a twig that is going inwards or sideways, you are worsening the congestion within the bulk of the tree, and the idea is to have each individual branch continually springing outwards, such that the trunk of the tree has plenty of air circulating around it.

Like so many things in gardening, it is easier to demonstate than to describe, so I shall have to resort to a back-of-envelope sketch to show what I mean:

Here's a cross-section, if you can imagine that your tree has been cut in half.

The dotted lines show branches which have either become too long, or which have been damaged, or which have been shooting off in the wrong direction.

You can see that by cutting just below the outward-springing twig each time, the branch goes outwards in steps, rather than going sideways (congestion, ugly) or inwards (congestion, loses nice waterfall shape).

In a perfect world, each branch springing from the top of the tree would fall gracefully, complete and uncut, to the ground but - rather like those pruning diagrams in RHS manuals - real life is rarely as neat and tidy as we would like. Most weeping trees send twigs pinging out in all directions, so they need a bit of help to achieve this sort of shaping.

The branch in the diagram above has, you might notice, no side twigs at all - again, something which rarely occurs in real life!  There is always a balance to be found, between removing sufficient wayward twigs to get back to the "light, airy waterfall", and removing so many that your tree looks sparse and unhappy. This is a skill which comes only with experience, but all this means is that I can whizz round and do the job really quickly, whereas someone less experienced would just do it rather more slowly - with this sort of pruning, it is always a good idea to step back every few minutes and assess what you have done.

If you now go back and re-read the article about Pruning of Small Weeping Trees, it should make more sense.

And with regard to the "cutting at the node" aspect, then yes, cutting directly underneath an outward-springing twig or branch, without leaving a stub, is indeed cutting at the node. Leaving a stub is a bad idea, they tend to die off and then there is the risk of die-back. It is always better to make your cut as close as you can to the underside of the springing twig.

At this point I will also add a reminder about avoiding pudding bowl haircuts: don't ever chop off all the branches at exactly the same height above the ground. It looks terrible! Take a bit more time, to go round and shorten - if necessary - individually. This is one of those times where a "ragged" finish is actually something you should strive to achieve, as it retains a natural look. Weeping trees are not topiary, and they look "wrong" if they are chopped a regulation 10" from the ground.

I am not a big fan of cutting the tips of weeping trees - all it does is promote that twig to produce usually two or more new twigs, often pinging out in odd directions - but what are you to do if the twigs are sweeping the ground? My usual answer to this dilemma is to go back up that particular branch, and rather than chopping a few inches off the tip, I go back maybe a bit further and find a twig which is springing outwards (as per the sketch above) and cut the over-long branch just under that springing twig. This preserves the overall shape, and that particular springing twig will then have several months of growing and elongating before it starts to get too close to the ground. Again, easier to demonstrate than to describe.

Right, now a big wave to Brenda, all the way across the sea in Georgia, (*waves enthusiastically*) who asked me about two Kilmarnocks which were purchased several years ago, and which are no longer performing as required. 

The first one is described as being "alive, but a twisted mess" which suggests that it needs a good going over. Again, I'll suggest checking out the Pruning of Small Weeping Trees post, which details how to start with cutting out dead wood from the top, then thinning out what is left in order to get the form back.  This might well solve the problem, and it would be lovely to see a "before" and "after" photo!

Brenda says the second tree "no longer looks like a willow" and it has no catkins on it anymore. Without photos it's a bit hard to diagnose the exact problem, but it is possible that the top of the tree, the weeping part, has died off, and the rootstock has taken over. Usually, Kilmarnock are one type of Willow (a weeping type) grafted onto another type of Willow (non weeping) so Brenda's tree is probably now a "normal" willow tree, which would explain the lack of catkins, and which means that it will grow as big as an ordinary willow, ie far too big for a domestic garden. If this is the case, it will have to be dug out and disposed of, I'm afraid, but please do send me some photos of it before you take that drastic step, just in case! 

Unfortunately, it is not possible to propagate from the "good" one, as Kilmarnock are grafted trees - two types of tree stuck together for our delight and delectation. It is certainly possible to grow a new sapling from the catkin-rich material, but it won't look anything like the small, neat, shapely tree that it came from. 

There, I hope that answers those particular questions: do feel free to ask if you would like any further info - and I will try to take clear photos, next time I am presented with a weeping tree to prune!

And finally, as a general observation,  if you want a small, pretty, tree for a small-ish garden, I have no hesitation in suggesting Amelanchier lamarckii (pronounced Ammell-ON-sheer) which is a small, elegant deciduous tree, they have superb white flowers and interesting coppery-coloured foliage in spring, coloured berries in summer if you are lucky, and good autumn colour as well. 

Update: Brenda later sent me photos of her actual trees, so here is another article, specifically dealing with them.

Friday, 8 April 2016

Woad: germination trial


"Woad's the stuff to show, men: Woad to show your foe, men:
Boil it to a brilliant hue, then rub it on your back and your abdomen..."

Most of us know that silly song, and most of us know that Woad was used by the Picts (the Ancient Britons of Roman times) to paint their bodies blue, in order to terrify their enemies as they charged, naked, into battle.

Hmm, yes.

Leaving historical inaccuracies aside, Woad is a real plant, the scientific name is Isatis tinctoria: it looks rather like a cross between Solidago (Goldenrod) and a rather top-heavy Oilseed Rape (Brassica napus), being a rather untidy, upright, waist-high plant with clusters of small bright yellow flowers at the top.

See what I mean?

Apparently it is occasionally found growing wild in England, mostly on wasteland, which I found quite surprising: you will be looking more closely at the weeds next time you go out walking, won't you!

I know I will.. I'm certain I've seen this plant growing out and about, so it will be interesting to find the plants in question and to identify them.

Anyway, back to the plot: I was asked last year if I would germinate some Woad seeds, for a chap who makes his own dye, and who had struggled to find these plants for sale.  He had managed to buy some seed, but he didn't have much experience of growing plants from seed, so he asked me if I would kindly have a go for him.

Always game for a challenge, I said I would be delighted to give it a go, and earlier this year I started a couple of sets of seeds: one set indoors, one set outdoors. When working with unfamiliar seeds, it is usually best to split them up and try different batches in different conditions, taking notes all the while.

About a month ago, much to my delight:


I love it when the first tiny seedlings start to appear!

This is the indoor set, sitting right by the window so they get plenty of light.

This is the outside pot (right) as it is today: they get more light, but obviously it is much, much colder outside, and the indoor seeds germinated a month earlier than this one to the right.

This proves that Woad seeds are sensitive to temperature when it comes to germination, so already I have learned something about them.

Now all I have to do is grow on a dozen of them, until they get to a decent size!

Saturday, 2 April 2016

'Tis better to weed a patio by hand...

.. than to use weedkiller.

I can hear you all groaning from here - stop it! Yes, I know that the temptation is to get out there and lay about you with the weedkiller: who enjoys stooping over a patio for an hour or more, digging out beastly weeds from the cracks?

No, not even me: patio weeding is one of my least favourite jobs, because as well as killing your back/knees, it takes ages, and is very unrewarding, in that once you've done it, it doesn't look superb, it just looks normal again.  However, it is something that I do quite often, and over the years I have realised that it is actually better to do it by hand than to let the Client spray it to death.


For several reasons, which I shall detail for you here.

1)  aesthetics: if you spray it, you will then have to watch the greenery slowly dying for the next fortnight, until your patio is criss-crossed with dead, brown and black rubbish, which looks dreadful.

2) cleaning up: you will at some point have to scrape out and sweep up this debris, unless you want to look at it for several months - so you might as well have weeded it by hand in the first place.

3) only partial success: unless your patio has a very light sprinkling of fresh young weeds, weedkiller will not get all of them, and a few weeks later the older, larger, more deeply-rooted weeds will be popping up again, stronger than ever. This particularly applies to the worst weeds such as brambles, cinquefoil and alchemilla mollis (my pet hate for patio weeding), all of which will lurk deep in the joins and cracks, and will spring up and grab your ankles in no time.

4) even if your weedkiller kills all the weeds,  it will leave a mass of organic matter in the joins or cracks. All that dead plant material, even though it was "poisoned",  is nothing more than fertiliser for the next generation of seeds. So by spraying instead of pulling, you are laying down the foundations for the next round of weeds.

4) and finally the eco-argument: we use quite enough chemicals and poisons on our land, and this is one place where we can exercise restraint and can choose not to use them.

There is also the consideration of run-off: if your patio is edged by lawns or flower beds, then excess weedkiller can run off the slabs, or can run along the joins, and end up poisoning your precious plants or your lovely lawn, particularly if you spray over-generously, walk over the wet patio then walk across the grass... oops! One of my Clients did this once - he'd sprayed a brick path, and then walked over the lawn. How did I know? He'd left a trail of dying grass footprints...

So how should you tackle this problem?

Arm yourself with a small hand tool - I use my Daisy Grubber -  plus gloves, knee pads or a kneeler, 

... and a bucket or tub-trug for the bits.

Start at one edge, or one corner, and go all along one side of one slab, using the tool to lift out all the weeds. I either shove it in vertically, then wiggle it about to loosen the roots, or I place it underneath the main stem and use it to lever them out.

Then move on to the next one, and repeat.  It doesn't matter if you do all the N-S cracks and then all the E-W ones, as it were, or whether you start in one corner and work across - just make sure that you join up all the bits that you do, and don't miss any.

If the joins are clogged with soil, scrape that out as you go, and once you have finished, you can brush some sand, or some small pea shingle, into the gaps.

Once it is done, get some Pathclear - yes, we're back to weedkiller again! Except that this is a preventative measure: get some Pathclear and carefully spray it along each of the newly-cleared cracks. Don't wildly squirt the whole patio, that's wasteful and unnecessary: just spritz along each join or crack. This will help to prevent new weed seeds from germinating, and should keep it clear for the rest of the season.

Here's one I did earlier, half done:

Can you see where I have been? *laughs*

This particular patio can't be treated with weedkiller, and can't have the Pathclear treatment either - as you can see, it adjoins a lake and I am obviously not going to use any weedkiller so close to water, in case of run off into the lake. 

So this particular one, I have to do by hand, about once a year. But it's worth the effort: and by doing it once a year, the weeds are never big enough to put up much of a fight.

So there you have it, four (or five) perfectly good reasons why it is better to weed a patio by hand.

Oh, but try not to do it on the hottest day of the year...!