Planting around new apple tree

[Philthy]

I have a 2 year old KOR tree in my garden, planted four months ago (with the aid of some great advice from the regulars on this forum). I have a 1.2m diameter circle of bare soil around the trunk for adding spring mulches and top dressing, while the tree establishes itself. It is a half-standard on MM106 rootstock, from Keeper's. So far it is looking very healthy. I've been watering it late evening every other day in this hot spell.

I'd like to know whether this bare soil should be retained for the duration, or can I eventually grass up to the trunk with no ill effects?

To refresh, the soil is clay, but I prepared the planting site well with double digging over a 2.5m sq area, adding well rotted manure and sand/grit. Very hard work as the ground hadn't been worked before, but I'm sure I'll reap the benefit in years to come.

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On a separate subject:

FB, could you please provide an overview on the strengths and weaknesses of each rootstock, as has been your experience? I've decided to get a couple more trees. Size is less critical, but M25, unless used in conjunction with a tree which is naturally slow and weak, would still be slightly too big.

Thanks a lot.

[FB.]

I'd like to know whether this bare soil should be retained for the duration, or can I eventually grass up to the trunk with no ill effects?

I would judge that based on how well it grows over the next couple of years. The key to successfully establishing MM106 is to ensure that it doesn't go short of water, but also ensure that the ground does not waterlog; to perform well it needs a happy middle ground of not too dry and not too wet.

If it grows too well it might be desirable to let grass compete with it to encourage cropping instead of excess growth.
But if it doesn't grow as well as hoped, you may need to leave the area clear (perhaps lay some coloured slabs or plants in tubs or some gravel around the base to prevent other plants competing but to make the space less boring).

[FB.]

FB, could you please provide an overview on the strengths and weaknesses of each rootstock, as has been your experience? I've decided to get a couple more trees. Size is less critical, but M25, unless used in conjunction with a tree which is naturally slow and weak, would still be slightly too big.

All things considered, apart from its high vigour M25 is about average in most of its features (such as pest resistance, disease resistance, climate and soil tolerance).

It sounds as if you'd be better to stick with medium-vigour varieties on your originally-chosen MM106, or possibly M116 or MM111 to ensure the trees remain roughly equal in size. Whether MM106 does well in your soil remains to be seen and it may turn out that MM106 will not grow well.

I think you'll have trouble keeping anything other than a small handful of obscure varieties on M25 to the same size as an average or slightly large scion on MM106.

Orangepippin's site has a good summary of the major rootstocks:
Fruit tree rootstocks and tree sizes

However, rootstock performance will change with soil and climate.

[FB.]

Here's what I think of the common apple rootstocks (I may edit this later to fix errors or include more characteristics if I think of them):

M27:
Vigour: very small (1.25m in average conditions)
Anchorage: poor
Resistance to woolly aphid: poor
Resistance to crown rot: very good
Resistance to replant disease: average
Precocity: very good
Flooding tolerance: poor
Drought tolerance: average
Infertile soil tolerance: very poor
Hardiness: average
Preferred climate: cool, damp, fertile, slightly acidic soil
Tolerance of neglect: very poor

M9:
Vigour: small (2m in average conditions)
Anchorage: poor
Resistance to woolly aphid: poor
Resistance to crown rot: very good
Resistance to replant disease: average
Precocity: very good
Flooding tolerance: average
Drought tolerance: good
Infertile soil tolerance: poor
Hardiness: average
Preferred climate: cool, damp, fertile, slightly acidic soil
Tolerance of neglect: poor

M26:
Vigour: slightly small (2.5m in average conditions)
Anchorage: average
Resistance to woolly aphid: poor
Resistance to crown rot: good
Resistance to replant disease: average
Precocity: average
Flooding tolerance: average
Drought tolerance: average
Infertile soil tolerance: average
Hardiness: very good
Preferred climate: cool, damp, fertile, slightly acidic soil
Tolerance of neglect: average

M116:
Vigour: medium (3m in average conditions)
Anchorage: good
Resistance to woolly aphid: good
Resistance to crown rot: good
Resistance to replant disease: good
Precocity: average
Flooding tolerance: average
Drought tolerance: average
Infertile soil tolerance: good
Hardiness: good
Preferred climate: cool, damp, slightly acidic soil
Tolerance of neglect: average

MM106
Vigour: medium (3.5m in average conditions)
Anchorage: good
Resistance to woolly aphid: good
Resistance to crown rot: very poor
Resistance to replant disease: average
Precocity: average
Flooding tolerance: average
Drought tolerance: poor
Infertile soil tolerance: good
Hardiness: good
Preferred climate: cool, damp, slightly acidic soil
Tolerance of neglect: average

MM111
Vigour: vigorous (4m in average conditions)
Anchorage: good
Resistance to woolly aphid: good
Resistance to crown rot: good
Resistance to replant disease: good
Precocity: average
Flooding tolerance: good
Drought tolerance: good
Infertile soil tolerance: very good
Hardiness: good
Preferred climate: mild, dry, slightly alkaline soil
Tolerance of neglect: very good

M25
Vigour: very vigorous (4.5m in average conditions)
Anchorage: good
Resistance to woolly aphid: average
Resistance to crown rot: average
Resistance to replant disease: good
Precocity: good
Flooding tolerance: average
Drought tolerance: average
Infertile soil tolerance: good
Hardiness: average
Preferred climate: mild, damp, slightly acidic soil
Tolerance of neglect: good

It is worth noting that MM106 is the most variable performer, depending on how much rainfall (or watering) it gets. In areas with plenty of rain (or where the soil holds moisture well) it is an equal to MM111. In areas with dry summers it can be only half the size of MM111.

It is worth noting that MM111 is the most predictable because it is the least affected by varied growing conditions.

It is also worth noting that MM111 may be less vigorous than M25 in good conditions, but MM111 is an inherently tougher rootstock capable of growing in a wider range of soils and climates. In difficult growing conditions - especially dry, infertile or cold soils - the M25 and MM111 rootstocks may be very similar in size and cropping.

[Philthy]

Thanks a lot FB, great reply once again.

To clarify, assuming soil conditions are ideal for the chosen rootstock, if the vigour of the rootstock and of the scion are both average, the tree will still reach its maximum mature size, it'll just take longer. Is that correct?

The issues associated with MM106 and it's inability to cope with flood or drought, do these become less of a problem as the tree matures - does the tree develop resilience over time?

I think you'll have trouble keeping anything other than a small handful of obscure varieties on M25 to the same size as an average or slightly large scion on MM106.

Would you be able to recommend a couple?

Thank again

[yummersetter]

I would have thought that as the roots extend further they are more immune from variations in the weather. Last winter I dug drainage channels from around a lot of my MM106 trees as they were in squelchy lakes about 12ft square and 4 inches deep for months on end, and that at the top of the slope. Now I'd need to get a pickaxe to make a dent in the soil and the new growth is still putting on a couple of inches a week. The roots are obviously picking up moisture from further under the surface - the orchard is grass with a foot of cardboard / grassclipping mulch round each trunk to stop the grass overwhelming the planting. The growing grass insulates the roots somewhat I would think.
My trees were transplanted at 5 years old a few years back and there is no water supply where they are so they don't ever get watered in dry spells - the draining I did last year was an unusual intervention, as I was worrying about rots in the stock, but the ones I didn't deal with look fine.

[FB.]

Thanks a lot FB, great reply once again.

To clarify, assuming soil conditions are ideal for the chosen rootstock, if the vigour of the rootstock and of the scion are both average, the tree will still reach its maximum mature size, it'll just take longer. Is that correct?

I'm not completely sure what you mean by this.
With good pruning technique it is possible to keep a tree between half and three-quarters of the size it wants to grow to.
A tree in good growing conditions will grow faster, and have a much larger mature size than a tree in poorer conditions.

Perhaps a different slant on this might help, where we consider the tree as having a fixed-size root system regardless of the soil.....
Suppose a given rootstock, when mature, produces 100kg of root mass.
That 100kg of root mass in good soil would be enough to supply a canopy with 200kg mass, for a total tree mass around 300kg.
In average soil, 100kg of root mass might be able to supply 100kg of canopy mass.
But in poor soil - especially dry soil - that 100kg of root mass might only be able to find enough water and nutrients to support 50kg of canopy mass.

So the root system might remain about the same size at maturity, but the tree which it can support will vary depending on how easy that fixed root mass can find water and nutrients.

Some scion varieties naturally produce bigger root systems than others - often considerably influenced by having originated in a unique climate.
D'Arcy Spice is the ultimate expression of this: a small, very-slow-growing tree above ground, but a unusually large root system below ground which allows it to grow in virtually pure sand with very little water or nutrients - as long as the rootstock can handle it!

The issues associated with MM106 and it's inability to cope with flood or drought, do these become less of a problem as the tree matures - does the tree develop resilience over time?

As trees of any type mature they become more resilient, but MM106 will still be one of the most prone to crown rot or drought stress.

Would you be able to recommend a couple?

I would opt for a spread of seasons or uses.
I would also "hedge my bets" with M116, MM111 and M25, while choosing a variety with suitable vigour to match your Kidd's on MM106.

So perhaps slightly slow-growing varieties on MM111, or notably slow-growing varieties on M25. Maybe a fairly vigorous variety on M116.