A timely reminder from Monty on last week’s episode of Gardener’s World sent me down to the greenhouse yesterday afternoon to check on our stock of over-wintered Dahlia tubers.
Dahlias are perennial plants that over-winter by storing sugars in large tubers below ground. But these tubers aren’t particularly frost-hardy or water-proof, so they do require protection to get them through the wet British winter. So they were dug up, dried out and potted up in spent compost last November, just after the first frosts killed off the foliage.
They’ll soon (hopefully) be bursting into new growth, which makes now the ideal time to check them over and make sure they’ve survived their winter hibernation intact. Here’s how:
1. Quick Visual Check
Start by tipping the Dahlia tuber clusters out of their storage tubs, and have a look for any obviously rotten, shrivelled or split tubers. Remove those, either by very carefully cutting them away with a sharp knife, snipping with secateurs, or gently twisting the affected tuber, which carries less risk of accidentally damaging healthy tubers.
2. Manually Check Every Tuber
It’s important to check every singly tuber in the cluster, in case there’s one that looks fine but is actually rotten beneath its skin. Give every tuber a squeeze to make sure it’s firm and healthy, once again removing any of them that aren’t.
You’ll soon find out if a tuber is rotten. Luckily, squishy tubers don’t seem to smell all that bad, but there’s always a risk of squirtage, so don’t squeeze them too hard…
3. Clean Up and Re-Pot
Once you’ve cut, snipped or twisted off any dead or diseased material, you should be left with a clump of healthy tubers, attached to a section of stem. At this point, you can also divide large clusters of tubers. Sometimes they split and separate during the checking and cleaning process. Otherwise, a bit of gently pulling might reveal a faulty line that you can take advantage of.
As long as the section you break off includes one or more storage tubers and a section of the stem / growth node part of the plant, then you should be be able to pot it up and grow on a whole new Dahlia plant from it. We started off with five or six bought-in tubers and over the past couple of years have increased our stock to around two dozen plants.
Re-pot each tuber into a mixture of spent and fresh compost. You can use all-fresh compost, which isn’t a bad idea if you’re planning on keeping the Dahlias in pots year-round, but I’ve found found that if you’re planning on planting them out when all risk of frost has passed then a 50:50 mix of spent – you can re-use the over-wintering compost – and fresh is fine. Once the plants go into the ground they’ll be able to draw on the nutrients in the soil.
Hopefully your efforts will be rewarded with a glorious display of dazzling Dahlias from mid-summer right through to Autumn!
With the weather turning a little warmer and the immediate threat of frost receding this week, I took the opportunity to pot up our newly-delivered fruit trees. Even more importantly, I gave them a formative pruning to set them up for their future roles as small, hopefully highly productive, fruit-bearing trees.
Here’s how I went about it.
This is quite a long post, you might not have time to read it all. In summary: I carried out formative pruning on our three apple trees, training them towards a vertical cordon system. I then potted them up in Air-Pot containers, which they’ll stay in for the foreseeable future, all being well. (Please feel free to scroll on down and take a quick look at the photos, they’re quite self-explanatory.)
As I understand it: formative pruning takes place in the first 1-4 years of the tree’s life. The aim is to establish the framework shape and form that you’d like the tree to develop into, and encourage new growth in keeping with that concept. Pruning in winter, when the tree is dormant, generally removes the main, apical buds of individual branches and stems, encouraging new, branching growth from the buds further down towards the trunk. The result should be a bushier, denser canopy and more fruiting spurs.
Once the tree’s shape is well established, winter maintenance pruning removes any dead, diseased or damaged growth, thins out any congested sections and helps to keep the tree’s structure well-balanced, light and airy. Maintenance pruning can also be carried out in summer, mainly to control and manage any of that vigorous new growth that might be getting out of hand and ensure a trained tree conforms to type.
I started out by taking a close look at each apple tree in turn; assessing the existing structure, checking for damage or poor growth and deciding on where and how far to cut them back.
We’ve invested in 2-3 year old small bush trees, rather than maiden whips (single stem) or feathered maidens (single stem with a few small side-branches) to give us a head start on fruiting. As a result they each have between three and six established lateral branches, with one or two leaders. Apart from one or two evident pruning cuts, most of the growth had been left to its own devices, so a lot of the branches were long and quite whippy.
After much research and consideration, I’ve decided to develop our trees as vertical cordons, keeping them permanently potted up in Air-Pot containers. They’re all on dwarfing or semi-dwarfing root-stock, so shouldn’t grow too vigorously, but in order to keep a good balance between a relatively small root-zone and the amount of top-growth, I don’t really want them to grow much taller than two metres (six feet, six) or so.
Cordon Training – Modified Lorette System
Last summer I found a copy of the 1955 Garden Book Club edition of Fruit From Trained Trees by Stanley B. Whitehead, in a National Trust bookshop, for the princely sum of £1. On pages 23-46, Mr Whitehead discusses the establishment of a modern fruit garden that includes trained apple trees in such new-fangled (within the previous 30 years or so) shapes as “cordons”, “espaliers” and “pyramids”. Clearly Mr Whitehead’s words weren’t falling on deaf ears.
The aim of a cordon system is to maintain a single stem (unless they’re developed as ‘U’ or ‘double U’ cordons), with a strong network of healthy fruit-bearing spurs, like so:
According to the current RHS advice on cordons, oblique cordons are more productive, but that’s not really practical with the Air-Pot containers and the space we have available, so I’m sticking to vertical.
Mr Whitehead’s book also makes mention of the Modified Lorette system of formative pruning and a quick Google search suggests it’s a system that’s still very much in use today. In a nutshell (if I understand it properly) it’s a summer maintenance prune that takes all lateral shoots from the main stem or leaders back to three leaves, not including the basal cluster) and any side-stems on the laterals back to a single leaf. This should help to develop the fruiting buds that will provide next year’s blossom and fruit on fruiting spurs. So that’s what I’ll be doing in August.
In the meantime though, back to the formative pruning cuts:
This tree wasn’t too tall, but had three well-developed laterals with a distinctly downward-slant to them. I shortened those, and took about a third to a half off the twin leaders as well, cutting back to a strong, outward-facing bud in each case.
The second photo shows an example of a pruning decision: to cut at point 1 or point 2. I went for 2, on the grounds that those large, fat buds will hopefully bear blossom and even if we remove the fruit this year to help promote root establishment, it will be lovely to see the flowers in spring. And I can always shorted than lateral in summer if needs be.
This tree was a little awkward, with a double-leader (top-left corner of the pic) coming off from the main stem at quite an acute angle, and several whippy laterals lower down.
I’ve shortened the double leaders by around half, and the lowest laterals to four or five buds, depending on which was outward-facing. I’ve left one lateral, which is growing opposite the double-leaders, quite long to hopefully provide balancing weight and prevent the tree becoming too lop-sided.
This tree was, if anything, even more awkward than the Blenheim. The bamboo cane that was used to support it was distinctly curved and it looks like the tree has grown with a definite bowing of the trunk in response. So as well as a less-then-straight main stem, there are three main leaders coming from a v-joint at the top of the stem, and then a couple of quite leggy laterals and three or four skinnier side-stems further down.
I’ve done the best I can for now, reducing the leaders by around a third and pruning back the laterals to four or five buds. We’ll have to see what happens in due course.
With the formative pruning done the trees were all a bit more manageable and less likely to snag and snap on anything; time to transfer them from their training pots to their new Air-Pot homes.
Air-Pots are widely used by commercial growers. The walls of the pots are made up of small plastic cones with the ends trimmed to leave a hole. As the plant in the pot sends out roots, they eventually grow to the end of the cones and come into contact with the air. This dries and kills the root-tip, preventing further growth of that particular root and encouraging new root formation elsewhere. The result is a stronger, denser network of feeder roots, with little or no root-circling and no chance of the plant becoming pot-bound.
If you’re interested in Air-Pot growing, check out Alex Taylor’s blog at Air-PotGardener.com. Alex grows a wide range of crops in Air-Pots and provides plenty of photos of the root systems that develop and the harvests that he achieves. As far as I know he’s not directly associated with the manufacturers of the Air-Pot (although they really ought to be sponsoring him with a few freebies by now…)
Back to the potting up: first job, rolling up the plastic sheet around the base and applying a couple of screw-fasteners to construct the Air-Pots.
Next, fill the bottom and as much of the sides of the Air-Pot as practical with John Innes #3 loam-based compost, working it into all those outward-pointing cones. JI3 is quite a rich mix and should provide enough nutrients to give the trees an initial boost once they start to grow and leaf up later in the year. After a couple of months then I’ll need to provide supplemental feed on a reasonably regular basis to keep them healthy and of course, plenty of water.
Then it’s time to knock each tree out of its pot and check the root system:
Lovely. A bit of circling, but that’s easily dealt with by gently teasing the roots out from around the edges.
I then decided to apply a sprinkling of mycorrhizal fungus powder to each root-ball:
Mycorrhizal fungi are beneficial fungi that grow in association with plant roots. In return for sugars taken from the roots, the fungi helps the plant to take up mineral nutrients from the soil more effectively. Perhaps it’s not strictly necessary in the case of a potted tree, but if it aids root development in the vital first year or two, then it’s worth trying.
Finally, back-fill with the John Innes #3 mix and soak with a couple of litres of clean rain water. The results can be seen in the photo at the top of the post.
The trees are currently standing in the shelter of the shed. This is a temporary position and they’ll probably be moved around a couple of times as work progresses on the garden, until they’re eventually put in their final position, when they can be properly staked, and perhaps a support structure put in place, if it seems as though they’ll need one.
I’ll be covering fig tree plating in a separate post, and I haven’t potted up the Morello cherry just yet either, so that’s another post to come.
Thank you for reading, and if you have any questions or observations on any of the above, please feel free to leave a comment, below.
These shallots we’re given to us by Dad-in-law Guru Glyn beck in November. I had planned to plant them out round about December 21st (“plant on the shortest day, harvest on the longest…”) but the weather wasn’t quite right, and then we had a busy couple of weeks, and, well… I forgot. Until Jo asked me yesterday whether the shallots were in yet, and suggested that if I can’t plant them out (the ground is frozen today, and heavy rain is forecast for tomorrow) then I might as well pot them up and get them going.
So: two varieties of shallots were duly potted up in our barely-above-zero greenhouse this lunchtime; ‘Hative de Niort’ (front) and ‘Jermor’ (back). Hopefully as the temperatures start to rise a bit over the next few days they’ll sprout and root and can be put in the ground once the conditions on the plot improve a little, but will still have enough cold-exposure to split the bulbs.
May is a pretty mad month in the greenhouse as the seedling shuffle continues apace. Last month’s sown seeds are shooting like crazy. More new seedlings need to be pricked out and potted up daily. And larger plantlets are outgrowing their starter pots and being potted on at a rate of knots. I’m loving every minute of it.
In lieu of time to describe everything in detail, here’s a quick photo gallery to convey the general impression:
What’s giving you particular joy in the greenhouse at the moment? Let me know via the comments…