Experimental Rootstocks

What’s a rootstock anyway?

I don’t want to disturb you, but gardens all over the country are filled with trees that would make Frankenstein (the doctor, not the monster!) proud. These freakish plants are stitched together from the beheaded carcass of one tree and the dismembered limb of another, often from completely different species. And who’s producing these monster plants? Fruit nurseries, that’s who!

Silliness aside, almost no fruit trees are grown via sowing seeds or simple vegetative propogation nowadays. Instead, standardised ‘rootstocks’ are grown, then the top is cut off close to the soil and either a bud or a small cutting is attached. The new wood is from the variety whose fruit is actually wanted, and of successful the two genetically different bits merge. The rootstock handles everything below ground, and the ‘scion’ is the bit above ground you actually see.

Why do it this way? There are three main reasons:

  1. Many varieties of fruit tree are hard to propogate from simple cuttings and don’t come true from seed
  2. Rootstocks can be used to make the tree more or less vigorous than it might be on its own roots
  3. Rootstocks can often cause the tree to fruit earlier than it would otherwise

The most interesting thing about rootstocks is that often they are not even the same species as the scion. Apples are normally grafted on to very closely related apple species or hybrids, but pears may be grafted onto quince as well as pear, and medlars are basically never grafted on to other medlars but can be put on pear, quince or hawthorn roots. Plums tend to be on plum rootstocks, but those same plum rootstocks might also be used on apricots and other members of the prunus family.

Unfortunately, while there are quite a few standard rootstocks, very few are commonly sold so you normally only get 2 – 3 options per species/fruit, and those 3 are the same 3 everywhere. Here are the ones commonly used in the UK for the most common garden tree fruits:

[table “3” not found /]

And here’s a chart from Wikipedia showing the effect on size for apples:

Apple rootstock chart from Wikipedia user quercusrobur

Apple rootstock chart from Wikipedia user quercusrobur

Keepers, who I bought my most recent trees from, offers a bit more variety, but even they mostly stick to the common rootstocks. That’s why I was excited to spot a couple of new and quite rare options on their website, which I’ll describe below.

Mespilus rootstock

The first surprising rootstock they are offering is ‘Mespilus’ for medlars. Since the only species in the entire genus is the medlar itself, this really means using medlar rootstock. This is not offered by any other nursery I know of, and as late as 2011 Hamid Habibi of the same Keeper’s nursery regarded it as problematic:

I don’t know about Amelanchier and would also be interested if anyone has used it. Rootstocks for medlars is a problem. Traditionally Crataegus has been used but has the problem that you continue to get large amounts of growth from the rootstock even when the trees are fully mature. Quince rootstocks are better in that respect. I would be very interested in trying seedling medlar as rootstock but medlar seeds are very difficult to germinate. Would be interested to hear if anyone has had any success in germinating medlar seeds and how

In line with the fact it’s new, Keepers offer no advice about its eventual size, or anything else really.

Own-root Apple Trees

The other surprise rootstock is more a lack of rootstock. Keepers are now also selling a limited number of ‘own root’ trees, all as 2 year old bushes.

I first read about own root apple trees at Cool Temperate. The long list of claimed benefits include:

  • Better health
  • Better fruit set
  • Better fruit quality

The health claims are believable since most common rootstocks now are dwarfing, and they basically work by limiting nutrients provided to the scion and/or due to a slight incompatibility been rootstock and scion. It’s not surprising if that also renders the tree less robust in the face of pests and disease. In addition, because there are a few rootstocks, genetic diversity in orchards and gardens below ground is usually lower than above, which also makes the trees more vulnerable to disease.

Again, the big question is tree size. Keepers offers no advice, but Cool Temperate does. Here it is:

The only disadvantage of OR trees is that some varieties may be more vigorous than is usually wanted, though the average size of an OR tree is not large.  This can be seen when observing self set OR trees grown from seed along roadsides, railway embankments, footpaths etc.. These trees are often quite small, and even when large seldom exceed the height of accompanying hawthorns.

The typical size of spur-type OR tree is similar to a tree on m9, i.e. 2-3 metres tall;

non-spur types are typically between M26 and MM106 in vigour;

and a few vigorous triploids giving trees between MM106 and MM111.

Size of tree is best controlled, if necessary, by early and regular cropping, which diverts the trees energy.

Another interesting question is how these trees are produced. I know that plums such as Yellow Pershore used to be propogated by suckers, but the main method I’ve read about for own root apples is to graft the variety as usual, then bury the graft union. If the bottom of the scion is exposed to soil it will often root, and voila!, job done. If this takes more time, it might explain why Keepers are only offering 2 year old trees. There is more about this here and here.

Cool Temperate has never, to my knowledge, actually sold any own root apple trees, despite promises that they were on the way. So it’s good that someone else has actually done it commercially. The only issue is that, probably due to the manner of production, only bush trained trees are available.

Are Chaenomeles Self-Fertile?

Following on from yesterday’s post, I found this paper.

Pollen viability for Japanese quince was normal as inferred from germination tests in vitro. A high self-incompatibility system prevails, which was confirmed both by controlled pollinations in the field, the study of pollen tube growth by fluorescence microscopy, and counting of final fruit set. The high amount of defective pistils commonly found in Japanese quince plants is probably not the single most important factor that influences yield. Instead, the compatibility between seed parents and pollen parents seems most important. The deviations found during embryo development in a normally developed pistil were not sufficiently frequent to decrease yield.

To ensure good fruit set and high yield, Japanese quince plants must be cross-pollinated. None of the genotypes studied showed satisfactory fruit set during all three years when self-pollinated.

So it looks like my suspicions about the (lack of) self-fertility in flowering quinces might be justified.

Shady Chaenomeles

I’ve been pondering what should replace the blackberry which I ripped out in haste, and I think the answer might be some flowering quinces. I think everyone knows these, but if you don’t they’re thorny little shrubs with red or orange flowers and hard acidic fruits. And I happen to have some waiting in pots already.

Chaenomeles japonica, picture from user Willow on Wikipedia

Chaenomeles japonica, picture from user Willow on Wikipedia

I’ve tried growing them for at least the last four years, as part of my collection of less common fruits including japanese wineberries, honeyberry, and aronias. But until this year the damn things just wouldn’t fruit much. They’d flower prolifically, then… the flowers would drop off eventually and that’d be it. So in a last ditch effort to get somewhere I relocated my existing plants into pots and put in a different variety.

And guess what happened? All my newly relocated plants fruited heavily. I’m not sure why but I have a few suspicions:

  1. Stress from tearing them out could promote fruiting
  2. They might have liked their new potted location more than their previous location
  3. They might not be very self-fertile – Martin Crawford says they are, but my experience suggest otherwise

I suspect (3) since I’ve had the same problem in our last two houses/gardens, and the relocation when we moved didn’t do much for their productivity.

The other issue is that thr ex-blackberry site faces north-west, and I’ve also seen conflicting advice regarding their shade tolerance. Creating a Forest Garden has this to say:

I regard these as more versatile crops than true quince in a forest garden. The flowers are much hardier so they are reliable croppers, they ae shade-tolerant, and the fruits, while acid, have a wonderful range of lemon and orange citrus flavours.

Conditions: tolerates most soils and a lot of shade.

Similar comments from the late Patrick Whitefield:

They can be grown in light shade, free-standing or against a wall or fence, including a north-facing one.

Other authors and sites are a bit less enthusiastic about flowering / fruiting potential on a north facing wall.

The varieties I have are:

  1. Fusion (new, already planted elsewhere)
  2. Crimson and Gold (new, in pot)
  3. Cido x 2 (old, in pots)

All are varieties that are supposed to fruit well.

Under the assumption that they might not be self-fertile as claimed, I think I’ll pair up a Cido and the Crimson and Gold in the 4m where the blackberry used to be and see what happens. If the worst comes to the worst they can always go back in pots again.


Recently I’ve been reading The Sceptical Gardener by Ken Thompson, which contains a collection of the articles that he wrote for the Torygraph over a number of years about botany and the science behind gardening. In one of those articles he praises Soilscapes, and I couldn’t agree more.

For those who don’t know, Soilscapes is an online app created by Cranfield University which can show you how the soil varies around any given location, and can also predict with pretty good accuracy what kind of soil you probably have in your garden. Of course, this is based on fairly coarse data, so if your particular garden is 95% builder’s rubble it’s not going to pick it up, but it is quite impressive.

Here’s what it says for my garden:

Screenshot_2016-01-06-21-08-21 crop

Screenshot_2016-01-06-21-08-31 crop

And… it’s kind of true. My garden is a bit odd actually, since there’s almost a line running through it. I have parts which match the description pretty well, but towards the north half of the garden the heavy top-soil gets thinner and the subsoil is quite light and well drained. Possibly this is to do with the fact that my band of “base-rich loamy and clayey soils” is surrounded by a sea of “Freely draining lime rich loamy soils”, and I may well be straddling the boundary despite what the map says. What is definitely true is the lime rich part, since if you dig around 2 meters down you hit a layer of whitish rock that looks pretty like limestone to me.

Anyway… it’s free, pretty, and a good approximation of the truth. Two out of three isn’t bad!

Tree Pictures

Beurre Sterckmans Pear

This is the Beurre Sterckmans pear on Pyrodwarf. I’d guess it’s maybe 1.3 – 1.5m tall, and already has some small side branches. Unfortunately they’re all too low – the tree needs to branch above 1.2m at least, so I’m going to have to prune back the existing branches. For the same reason I’m not going to prune the top off it – I want it to grow it as a central-leader standard or half-standard.

The spot it’s in gets the most winter sun of any point in my north-ish facing garden.


Cockle Pippin Apple

This is the Cockle Pippin apple on M25. It’s a similar height to the pear, but without any side branches right now. Again, I won’t prune the top off – I’ll just let it get on with it next year, since I want it to go up rather than out. Around it you can see some of the straw which Keepers used for packing, and which I’ve reused as an additional organic mulch beneath the black plastic sheeting.

The tie is a pair of old tights, since proper tree ties were the only thing I forgot to buy.


The New Trees Are In!

I was at home today looking after my son (he’s one and a bit and spends most of the day marching around like the Energizer Bunny), so I arranged for this year’s bare-root fruit trees to be delivered while I was around.

I was a bit nervous as a previous “overnight” plant delivery by TNT in December took 5 working days to show up, and the carrier used for today’s delivery had terrible online reviews. Seriously, look at the reviews for Tuffnells here. But despite my worries, the trees showed up at 1pm with no problems or damage to the packaging, so for me they did much better than TNT!

I ordered from Keeper’s Nursery since unlike most they stock more vigorous rootstocks like M25 and Pyrodwarf. The new trees need to survive a lot of root competition from nearby hedging and branch high for the same reason, and I’ve also not been very impressed with the performance of Quince rootstocks in my garden. So I figured better be pessimistic and have to summer prune to reduce vigour than end up with two trees going nowhere fast.

The varieties, with a description quoted from the books of Joan Morgan, are:

  • Cockle Pippin apple

UK raised c1800 by Mr Cockle, Godstone, Surrey

Quite rich, firm; some aromatic quality in a good year.

Widely popular in C19th; grown gardens and for market

F11. T2; uprt. C heavy. P m-Oct. S Nov/Dec – Mar.

  • Beurre Sterckmans pear

Syns: Doyenne Sterckmans (F), Sterckmans Butterbirne (G)

Belgium: raised by Sterckmans at Louvain/Leuven before 1820; brought to notice, propagated by J.B. Van Mons. Recorded as Beurre Sterckmans 1850; widely distributed.

Striking fruit and tree in the autumn; pears ripen to deep rose flush over pale gold. Fondant, fine textured, juicy; white to pale cream flesh; can be syrupy sweet, quite perfumed. Invaluable part of Victorian collections, it followed Winter Nelis and lasted for a further month; still esteemed in 1920s, though said to be reliable only in southern England.

Fruit: size: med. (72-88mm high x 66-75mm wide). Shape: short pyroform; eye-end – often rounded ribs, slt./prominently bossed. Colour: prominent/mod. red flush over greenish-yellow becoming pale gold; little russet; many russet lenticels, appear red on flush. Eye: open; sepals usually linked, reflexed, often broken tips. Basin: shallow/med. width, depth, slt. wrinkled. Stalk: med. length; qt. thin; inserted erect/angle. Cavity: slt./qt. pronounced; often ribbed.

F* late, (F29); large flowers. T3; uprtsprd.; well spurred; prone scab; brilliant autumn foliage. C gd. P mOct. S Nov/Dec – Jan.

It might seem that I was going for a Victorian theme, but in fact both trees were chosen simply for a combination of:

  1. Upright habit
  2. Ability to pollinate / be pollinated by other trees in the garden
  3. Late cropping and fruit that keeps well – since these are not dwarf trees, there’s no point producing 10s of kg of fruit that all have to be eaten in a week.

I managed to just get the trees in the ground before it got dark, although it was a bit touch and go. It’s a bit tricky to plant bare-root trees on your own – you need a calm day and then to gently mound up the soil around the roots to make them stand up so you can fill in the hole, but at the same time you need to keep the soil loose so you can still adjust the inclination of the trunk before firming down the soil. I’d already dug the holes and bought essential supplies though (manure, bone meal, rootgrow, stakes, …), which meant half the work was done before the trees arrived.

Unfortunately, twilight isn’t a good time to take pictures, so there aren’t any at the moment. I’ll take and post some tomorrow!