I am a beginner orchardist and have been reading lots of sources about ideal soil planting height and mulching and am confused about what seems to be contradictory common bits of wisdom:
Plant trees such that the crown / root flare is above ground to reduce disease pressure to trunk and improve air flow to roots.
Add lots of mulch to improve soil temperature fluctuations, hold soil moisture, and improve soil texture. Important to keep away from tree directly so less humidity at trunk, thus mulch in a donut shape around tree.
Even if you avoid mulching directly around a tree, the soil level will gradually rise and be higher than the tree crown. If I mulch annually with 6 inches of chips, say that breaks down to 1/2 an inch of soil. After a few years, the crown will be a few inches below the new ‘ground level’ as a crater mound gradually grows around the tree. Wouldn’t this be bad since water would accumulate in the central crater near tree? Or does the tree somehow raise its crown to keep pace with the rising soil level? What am I missing to resolve this paradox.
The reason I’m overthinking this is I foolishly planted some trees into clay soil and they have been struggling. At the suggestion of @alan, I dug up the smaller ones and build mounds for them before replanting to improve drainage. For the larger trees, however, I have been overcompensating by mulching the hell out of them to improve soil texture, but worried that the root flare will end up being too deep as new soil keeps accumulating on top.
So some people over dig and due to settlement will plant the root flare slightly higher expecting settlement and mulch is fine if you think about natural forest setting leaves and wood are constantly building up… that doesn’t bury the tree the tree is able to put out a lot of feeder roots to utilize these nutrients
If you’re planting any grafted trees you just have to be aware of the graft Union and not bury it then again some guys are purposely burying their graft to protect against cold death so now I really confuse you and me LOL
It will probably vary a lot based on your precipitation patterns (e.g. 6a in British Columbia vs 6a in a high desert vs 6a in Kentucky will have different guidance), but there have been some good threads here discussing the challenges of planting in heavy clay, for example:
I don’t believe I’ve ever seen an apple tree killed by being planted too deep, and considering that trees create actual mass from more than the soil, but also the sun and air, they naturally often gradually raise the soil above the original crown. I’m not saying you couldn’t kill any tree that is in a root ball and then transplanted too deep, but such a tree is already under great stress from losing most of its functional root system.
I have seen commercial orchards where plenty of trees were planted below the graft union and it never affected the relative vigor of the trees- at least once they were established, so you shouldn’t assume that all varieties will send out roots if the scion is buried or that such roots will excessively stimulate a tree, especially if it’s already bearing fruit.
Back in the 18th century it was a thing to plant pears grafted to quince well below the union so the quince would survive New England winters. The method was supposedly quite successful. The trees survived and remained dwarfed.
Depending on the age and rootstock it might not be necessary to keep root flare at soil level.
For example reasonably young apple tree’s on rootstocks that easily root can be planted way deeper than they where in the nursery. They will make new roots where buried.
It is important to keep the graft union above ground!
When mulch brakes down, a large part gets transformed to gas, and floats away. Another part is water soluble and is taken up by the roots or washes away. Some material is also taken up by soil life (like worms taking down leaf’s in their “tunnels”)
As long as the mulch itself is not burying the trunk i think your fine.
I would pay extra attention to root flare on rootstocks that are seedling and don’t root readily (hard to layer or strike cuttings)
Rootstocks that come from a stool-bed have wide tolerances for planting depth. (pay attention to graft union though)
This advice would be pretty species-dependent, right? I’d assume it’s fine to plant many trees with the graft union buried unless:
(1) the graft union has not fully healed, or
(2) you have chosen this rootstock for some specific reason (such as for rot resistance, salt tolerance, or dwarfing effects).
I’m sure there are particular species that will not take kindly to deeper burial, but some should do fine, and if you’re zone pushing that can give you a chance to have the grafted variety survive if the tree is frozen to the ground.
I have often seen it recommended that peach trees and other trees not on dwarfing rootstock be planted AT the union, I believe to reduce the chance of breakage at the point of union in heavy wind.
I haven’t seen exceptions to these recommendation involving anything besides dwarfing… although I can see how it might be a problem if a tree was on, say, nematode resistant rootstock, and a buried rootsystem caused rooting out of non-resistant roots above the graft, but I expect the problem would be widely recognized if it was real. I expect… not know.
Burying the graft union is more the exception than the rule i think.
Most cases you have the rootstock for vigor control. If you bury the graft union, and the scion roots. You loose (part of) that vigor control.
In a lot of cases you have the rootstock for specific resistance to soil conditions or pests and diseases. Having the scion root could lessen all those resistances
for example woolly apple aphid. Woolly Apple Aphid | WSU Tree Fruit | Washington State University
Although i think it’s not completely clear where the resistance for woolly apple aphid comes from. I think the nymps don’t like the roots of certain rootstocks and that helps in the resistance of the tree grafted on that rootstock. (since nymps like to overwinter on roots)
But also diseases like crown gal Fact Sheet: Crown Gall – Database of Apple Diseases
Could get worse when the scion roots.
Another issue is, when the scion is unable to root.
The above and belowground section of trunk on tree’s looks different. (see picture below)
When a rootstock or scion that can root gets buried. It’s surface/structure usually changes. And it can withstand the dark moist environment of being buried. If you burry a think woody stem it can get diseased and rot if it is unable to adjust to below ground environment.
This is often the case with rootstocks that get sown because you can’t layer them. And in a lesser degree (but still often advisable) for tissue culture rootstocks.
See my below picture of a Quince adams and Pyrus communis (seedling) rootstocks.
Left is a Quince adams rootstock. You can burrie that to any depth you want (within reason. you don’t want to sufficate all roots by planting really deep in hash soil) up until the scion. If the scion can root and you don’t need the properties of the quince adams rootstock you can even burrie the scion.
Right side is a Pyrus communis seedling rootstock. You can clearly see the different tissue thickness, structure and color below and above the red arrow (planting depth)
If you plant this rootstock much above the red arrow. You run the risk of the stem rotting.
If you plant it much below the red arrow, you run the risk of the “rooty” stem drying out or being damaged.
planting depth (regardless of grafting place/ burying graft union) is much more precise for the seedling stock than for the layered stock.
It is tricky to see, i could not manage to get a clear picture. But on the left rootstock (layered quince) you can see a gradient of color. And if you plant that deep the green colored bit will get lighter to white. And change to a “below ground state”
The pyrus seedling will not.
i only know of 4 cases where you want to burry the graft union.
1 Nurse root. Here you graft a rootstock or root of a weaker growing plant or species onto a scion of a tree that can root, but does not root easily enough for easy stool bed propagation. (some tissue culture rootstocks come to mind)
Here the point is to basically take an assisted (by grafting) cutting. And eventually get an own root tree.
2 interstem for vigor control MM111 with M9 or B9 interstem comes to mind. Here the M9 or B9 graft union can get buried to lessen the suckering tendency of MM111 when forced to dwarf. Here the more vigorous variety is on bottom and not the top. (usually it’s the other way around when the scion roots, it is more vigorous than the rootstock and overtakes it. Thus negating the need for the rootstock)
3 your mentioned example of frost tolerance. Here you will likely run into the risk of the scion making it’s own rootsystem and eventually rejecting the original rootstock and thus no longer benefiting from the properties of the original rootstock.
4 fringe cases. In my country there are some anecdotal accounts of Reine Claude Verde (RCV) also called green gage that where flooded during a river flooding and rooted on their branches. Producing better than before. But you could fit this case into the nurse root category. Because you are basically producing an own rooted tree.
In my country there have also been tests done with using spend mushroom compost to mulch the graft union of pears grafted on quince C (frost sensitive quince rootstock) to lessen winter damage.
The mulch however is removed during the growing season. And the scion is not allowed to form it’s own rootsystem. I would not really classify this as burring the graft union. But more as temporarily mulching or winter protecting.
In general i think the advice of not burring the graft union is pretty universal. And if your in one of those exception cases. You probably know enough that you know why you can deviate from general advice.
More on topic
When mulching with wood chips i would be even less worried of the buildup burring the tree crown if the rootstock of that tree is stool bed produced (layered)
I would pay slightly more attention if the rootstock was sown or came from tissue culture.
PS: i just saw your interested in avocado’s etc. I have no experience with those. My above statements are mostly about apples pears plums cherries etc. Tropical fruits might be completely different.
I think in my orchard i could have gotten experts to give me at least several different opinions… likely at least one or two opinions that would tell me not to plant an orchard there at all.
So instead i just did trial and error. I planted one tree in a mound and one the old fashioned way.
The tree in the mound thrived the one buried below soil level struggled.
So the 30 trees that i just planted all got mounds. And the stuggling tree was dug up to reveal that very little root growth happened at all. Still alive but barely. Could have been something else that caused it…but my gut said that it didnt like the old worn out clay soil.
I think i did a very good job at top dressing the stuggling tree. Aged wood chips, manure, grass was mowed onto the mound… leaf litter applied in the fall. When i dug it out the worms were all gathered and living the good life… so without a doubt in the years to come that top dressing would have created a nice aerated soil structure full of nutrients… but not enough time to help the young tree create a root structure.
My neighbor has the same soil as me and he attacks his with gypsum. His soil is dead and nothing but weeds and crabgrass now. He had bumper crops for a few years though.
Mounds and organics to feed the tillers and biome are my hope to have a nice orchard in an otherwise unlikely area.
Just on my property i have several variations of soils… in my blackberry/raspberry orchard that soil is mostly sandy loam…its pretty evident. We grew tobacco and corn there for decades and the folks before us did the same. My dad plowed in vetch and grasses every spring for all of his tenure. I let it lay for 5 years before i planted anything. Its perfect for my berry patch.
On my new orchard it is my front yard which is a little over 200ft by 200ft.
When we moved here there was an apple tree and a peach tree in the yard along with some willows and catalpas Over the years the peach and apple died… i think they were likely grown from seed in the early 1900s
So that area just got mowed for decades… i dug some holes to see if it was worthy of another berry orchard and wasnt happy with the soil. Heavier clay with lots of rock. Maybe 100 years ago the farmers removed the good soil and put it in the back yard… which is totally different soil altogether. I know that whomever lived here in the 1800s were very industrious… they built wells and rock walls and lots of structures deep on my land.
So to answer your question my front yard makes a good lawn but other than that i think its a very poor choice for an orchard… I think with adding top amendments and letting the grasses top out and develop better soil structure that i have a chance at at least a decent personal orchard. Maybe half of it will fail…but to me thats better than mowing or just looking at a flat unusable yard. I have other things growing around the borders like elderberries, grapes, black rasps, red rasps and some blackberries… those seem to be doing good.
Climate is like a deciduous rainforest… wood decks rot here… lots of moisture always.
My backyard is ultra prime soil… my family grew gardens and the families before us grew gardens… the soil is deep and rich. I turned it into my personal blackberry and raspberry haven… Everything does well there.
My neighbors farm is different than mine. It has always been owned by folks that grow crops based on how much fertilizer they apply. I think in my lifetime it has been owned by 5 families. The soil is worn out…exhausted.
There was an old man that lived there when i was little and he didnt farm but had a garden in his backyard. It was deep and rich… he put every thing that was food related back in that garden…compost galore. Had chickens penned in there when he wasnt growing things. Biggest turnips and best potatoes and tomatoes that you can imagine. Beautiful garden.
I told my current neighbor about this garden and he decided to park his cars on it… i think he plans on putting gravel over it. He instead wants to grow things on a bottom in front of his house that i have never seen much of anything grow… The tobacco and corn that was grown there was sickly. He has the help of local extension agents and they were the ones that told him to use gypsum… i think he is going to use something different next year. They are working on a plan as far as i know… likely some kind of fertilizer.
So long story short my farm has mostly been cover cropped and had folks that lived with the land… his farm has mostly been folks that used the land. So soil is different.
Heavy clay is a tough one for fruit tree’s. I think mounds and lot of organic material to improve soil structure and possibly drainage is the way to go.
I read somewhere about tests with giant daikon radishes to brake up clay soil and introduce organic material. I have no actual experience with it. But it might be a fun experiment to plant a few and see if it improves things.
I think they where called tillage radish or something.
Dont underestimate the power of worms…they till and aerate 24/7.
I planned my orchard last summer and where i was going to plant trees i laid down manure, shredded leaves and woodchips. Just laid it in piles above the grass. I pulled that back when i got my tree shipments in and the soil underneath was like fine coffee grounds… i could poke my fingers deep in it. Full of worms. I have several loads of topsoil that i trucked in from a goat/chicken/hog/rabbit farm and it has been sitting for 2 years… that is what i used for my mounds and all of my raised beds of garlic and strawberries. So i think with the mounds and the worm tilled ground below that i have a better chance of success in my otherwise worthless ground.
I will continue to add organics to the walkways and let the white clover go to seed and keep it going. Hopefully the trees leaf out well and keep adding their own leaves to the formula.
I am basically doing the same thing. Out of the 30 or so trees / bushes that are struggling I dug out half and transplanted them onto mounds. The other half I have been mulching heavily, about a foot of woodchips and grass clippings a year (care to avoid touching tree). I am planning on giving them about 2 years, and if they don’t turn around, I’ll rip them out too and put mounds in.