Fruit Trees in Clay Soil

Looking for some suggestions on how to prep my space to plant some fruit trees.

I have very heavy clay soil and would like to plant a few fruit trees in the next month. A few I'm thinking about are fig, citrus and persimmon. I have heard and read different things about whether or not I should amend my soil or just plant and let the trees become adjusted to the natural soil that I have. Would it beneficial to plant the tree and then sheet mulch around the tree? I live in a mediterranean climate and am concerned if I plant my trees on mounds that they will dry out more quickly.

I was also reading a big about planting trees on hugelkuter beds but didn't find any substantial information as to whether or not anyone has had success or failure with this approach. Any advice would be welcomed.

Hi Alicia.

First, I would suggest Redhawk's soil primer. The link is posted below.

https://permies.com/t/67969/quest-super-soil

With clay, I like to add organic matter and get it in the ground, then plant things that will add more organic matter. There are a few recent and active posts up on this forum about dealing with clay soils. You might want to read them over, as a lot of the issues there will apply to your situation.

Next, I think you're right about planting on mounds, although it would depend on how wet it gets seasonally, as well. Mounds are usually used to increase drainage until the tree's root zone can start affecting that on its own.

You might need to address drainage with heavy clay. I would think about digging miniature swales on contour, and digging whatever organic matter is available into them. I prefer wood chips, as they are easy to get for free where I am from urban arborists. Some would also suggest biochar (specially-produced compost-innoculated charcoal that acts as a microbe habitat to host microbiota), as it would help host soil microbiota,

Also, when using hugelkultur with trees, you never plant the tree in the top of the hugelbeet. The loose soil structure is great for spreading roots, but rarely do trees root well enough in a hugelbeet that they can then resist even moderate winds. It is for that reason that the trees are usually started near the foot of the hugelbeet, where they can still benefit from the polyculture of the hugelbeet and its water retentive qualities, but not be blown over because the roots are in a pile of loose soil above the ground.

With heavy clay, it is sometimes good to work it mechanically, like with a broadfork. The idea isn't to flip the soil, but rather just to sink the tines in and push down a little on the handle, aerating the sub-soil. If compaction itself is an issue, that will let the whole area breathe a bit, soak up a little more water, and maybe even establish a little groundcover.

Trees of any sort are an investment, so unless you've just had one, it wouldn't be a dumb idea to think about getting a soil test done, including micronutrients. Without knowing that, suggesting solutions in anything but a general soil-health way is a little hit-or-miss. Do you know what pH your soil has? There are mineral dusts that you could add to your soil before forking it as described that could be beneficial for drainage and opening up soil structure in clay, but without knowing at least the pH, that is also difficult.

Best of luck. Please let us know what you do and how it goes.

-CK

hau Alicia, The best thing to do in my opinion and this has worked very well for me;
Dig the hole 3 times wider than the soil root ball around the tree and only as deep as the soil root ball or just a bit deeper to loosen the soil some there.
Set the tree into the hole, making sure the root ball soil level is even with the ground surface, water the root ball as you are back filling with the removed soil, add compost if you have it so it makes up any loss of soil from rocks (remove all large rocks, any smaller than a soft ball are fine to go back in).
If the soil looks wet when you are finished back filling, add three stakes equidistant in a circle around 2 m from the trunk and loosely tie ropes around the trunk and to each stake. (these are for helping it stay upright in windy conditions, this only needs to be in place for the first year, check often to make sure there is no trunk damage, remove if there are any signs of trunk damage).
 I have red clay subsoil and every tree I have was planted down into this red clay, all have thrived quite well by using this planting method.

Redhawk

I've got heavy clay soil and I grow all the trees you list.  They are all thriving.

Clay is wonderful for trees, but you need organic matter on the surface of the soil or it'll bake into a brick-hard impermeable parking lot.

As Bryant has said, dig your hole 3 times the size of your pot.  Don't dig too deep, as it will cause your tree to settle and sit too low if you do.  You want the sides of your hole to be irregular and not perfectly round and smooth, or the roots will hit that smooth wall and just circle around in a loop.  Don't amend your soil with anything but crumble it up loosely so that the roots can easily move through it once you back fill.

When you pull your trees from the pot, gently dig down along the trunk until you find the first lateral root.  Often, nursery staff will plant the left-over bare-root stock that they get in the spring.  They'll bury the trees too deeply, and so part of the trunk is actually below the soil line.  You want to plant your trees so that the trunk is above ground and the roots are below.  As you sit your tree in the hole, the first root should be an inch or two above the level of the soil outside the hole.  That way, your tree is planted slightly higher than the surrounding soil.  People think, "I'll plant it a bit low, and then all the water will seep into the hole and it will keep it well hydrated."  Wrong -- trees that sit in low wet spots tend to rot or suffer from fungal diseases.  Plant it right at soil level or slightly higher.

If there are roots that have run around the outside of the pot, gently untangle them.  You don't want them to slowly strangle your tree.  If you are unable to untangle them and pull them outward, then snip them off with a sharp set of shears.  As you place the tree in the hole, take a few minutes to gently direct these roots outward.  

Slowly backfill the soil, again, using the soil you removed from the hole.  If you were to add a bit of WELL AGED compost at this time, it wouldn't be terrible, but it's not necessary.  Do not add anything that will burn the sensitive roots -- this means no manure or fertilizer.  The ground should gently slope away from the trunk (a drop of an inch or two) until it reaches the outside of your moat --  a 4 inch circle of soil that will hold the water in when you give your tree a drink.  Usually, you will need to find some additional soil, as there is never enough from the hole and the pot to sufficiently build a little round berm around your hole.

Ultimately, you'll want fungal dominated soil to form a symbiotic relationship with your tree roots.  If you have a mature fruit tree in the area where mushrooms pop up out of the ground after a hard rain, go get a couple of scoops of that soil and put it next to the root ball of your tree.  Fungi are fun guys.  Your tree will be happy to bond with the fungal network.

Gently pack the soil around the tree.  Don't stomp around heavily on the soil you've just backfilled.  You'll be crushing those little roots and will be needlessly pushing all the air from your soil.  As you water the tree, you'll see it compress a bit.  You may need to add another shovel-full of soil here and there to get it back to level.  Again, you don't want a low spot or depression where water will sit over the root ball.

THEN -- the key for clay soil, mulch mulch mulch mulch mulch.  Wood chips.  Coffee grounds.  More wood chips.  Compost -- so that you get a couple of zillion bacteria and other microorganisms into that freshly loosened soil.  Aged wood chips -- so that you get a nice fungal community going around the tree.  And if you have some on hand, more wood chips.  4 to 6 inches of wood chips.  Pull them out away from the trunk of the tree, but starting a few inches from the trunk, lay down a thick layer of biomass (chips, leaves, old sticks, compost).  The biomass will keep the soil cool and moist, will encourage fungal growth, will be a haven for worms, and will keep that clay from compacting.  The worms will move the organic matter down into the soil profile in the years to come.  With clay, you really can't have too much mulch.  

Stake your tree as needed.

Water deeply and as your tree gets stronger, less frequently.  Thus, you'll train the roots to go deeper in search of moisture.

If you had to trim the roots, you'll need to trim a corresponding amount of branches above ground.

Citrus do not like it too wet.  Let it dry a bit between waterings.  Maybe water every 3rd day initially, and by the second year, only twice a week.  

Figs are pigs.  They never seem to get too much water.  

Persimmons like a moderately moist soil -- keep it evenly moist, but never standing water.

Good luck.

Great post Marco. Thank you.

Did I mention wood chips?  I forget.  I think I mentioned wood chips, but if I didn't . . . wood chips.

If you've got clay soil, wood chips.  Clay is one of the most fertile kinds of soil because clay molecules are negatively charged and that enables them to grab hold of positively charged nutrients as they pass through the soil profile.  But only if there is adequate humus to break up those strands of clay.

Think of clay molecules like a stack of paper plates.  They tightly mold themselves to the one above and below, leaving no space for potato salad.  Clay molecules will form long chains and will tightly mold themselves so that water and air cannot penetrate.  This is why we use clay to make pottery.  Have you ever seen a big lump of potter's clay?  There is absolutely no space for air or water.  Clay is great for a coffee cups, but lousy for a growing medium.  UNTIL you add carbon.  Carbon breaks up those long strands and brings tremendous potential to the fertility of clay.  

Adding biomass to the surface of your soil is the strategy.  That's how a forest does it.  On an annual cycle, leaves fall to the forest floor and mulch it, and worms incorporate it down into the soil.  More mulch, more carbon, more worms, more incorporated humus.  In planting your fruit trees in your back yard, incorporate the same strategy.  If you don't have a compost pile, start building one in the neighborhood of those new fruit trees.  Then turn it and slowly "walk" that pile around the whole area with every turn.  In a couple of years, your pile will have traveled around and between your trees, enriching the soil and feeding the micro-biological life therein.

If you want to add another element to your newly planted trees, sew a handful of cover-crop seeds into the basin around the newly planted tree (the area between the tree trunk and where your mulch starts).  Those cover crop plants will pump sugars and starches into the soil—what they call "root exudates"—into the soil.  This feeds the soil biology (bacteria, worms, anthropods, other biota) and will cause the soil to become black and crumbly (like cottage cheese).  If the soil structure is loose and crumbly, the roots can more easily spread out.  

Yeah buckwheat and vetch!

Thanks for all the advice, I'm finding it very encouraging. Marco, just to be clear, what you are recommending is planting the trees in the soil as is, with the hole being dug as you suggested and then adding wood chips on top of the soil rather than adding anything to the soil? Would you recommend punching some holes in the clay below the hole that I have dug? It seems like I may be successful using this method, creating a moat around the tree as well as placing it below a swale?

I will keep you all posted on how this turns out, I plan on planting a few trees in late January or February which seems to be a good time around here. (I'm in Three Rivers, CA on the edge of the San Joaquin Valley) For those of you who have fig trees, has anyone pruned them to stay relatively small and still produce a good amount of fruit? I have around 1/5 an acre but already have numerous oak trees that produce shade so ultra sunny spots are somewhat limited. I don't know anyone in my area that has fig trees in particular so I am curious if fig trees would grow well here in dappled sun since the summer months get so incredibly hot. I

Hi Alicia, i can't add to what has already been said about your soil but if you have as many deer as I have, you may want to think about making a 4 foot or so diameter cylinder of fencing around your fruit trees to keep the deer from eating them. Not just the fruit, but the bark, the leaves and the branches. They are tender vittles to deer. The bucks also can decimate a tree when they rub their antlers on the trunk. First hand experience. I was going to chase a buck away a couple of weeks ago while he was scraping bark off one my trees, he stopped for a moment, looked at me like I was crazy and he was right!

Good Luck!

Thanks Jack. Yes, I do have deer that come through my yard as well as rabbits and gophers and lots of birds. I was planning on wrapping the root ball with some kind of gopher wire to protect it and protecting the trees at the onset of planting but haven't made a longer term plan yet. It doesn't seem like it would be very efficient to put in a fence around each tree and I would rather not put in a large fence in the area where I would like to plant my trees. I wonder if there is a more natural type of "fencing" that I could grow around the perimeter of where I plant my trees. I would like to plant a few trees in a few different areas that aren't connected to each other because of the layout of my space. Any suggestions?

Correct.  Do not amend your backfill soil with anything.  Garden centers and nurseries will try to sell you a couple of bags of soil amendments (compost) to mix in with your backfill soil.  You don't need it.  They'll say something about "planting a $50 tree in a .10 cent hole" but research has shown that amending soil does nothing for the long-term health of the tree.  It's money wasted.

The worst case is that you create the "bathtub effect" for your tree.  Imagine digging a hole in hard clay soil.  And then you take that dirt and amend it 50-50 with wonderful soil amendments.  Now that "bad" clay soil is transformed, black and crumbly and rich.  What's not to like about that?  The tree immediately takes off and the roots shoot out into that beautiful soil . . . until they hit the side of the hole and come crashing into the hard clay wall.  So the roots turn back inward toward the lush, black, compost filled soil.  And within 2 years, you've got a root-bound mess.  The bathtub effect.  Water soaks into the bathtub while it runs off the outer soil.  It doesn't give the tree any incentive to push out and push deep.  Within a couple of years, it will actually set the tree back.

If I bought a bag of soil amendment, I'd dump it on the surface of the soil around the tree, but I wouldn't mix it into the backfill soil.

Yes -- moat.  Or more accurately described, a berm.  But push the berm out a good distance from the tree trunk.  If the edge of your hole is 2 feet from the tree trunk (4 feet across the entire hole), make the berm 3 feet from the tree trunk.  Mulch the entire basin with biomass, right out to the edge of your moat and even beyond.  Keep grass from growing inside it.  That way water infiltrates the soil even beyond the hole, and organic matter begins to work its way down into the soil profile beyond the hole.  You want to do everything you can to encourage roots to push out through the walls of your hold.  If you dig a swale to channel water toward your tree, be careful that they don't get saturated and never dry out.  As I said above, citrus doesn't like wet feet.  Clay will not drain readily, so don't plant your lime or blood orange tree in a self-created wetland and then wonder why it's turning yellow.  

Never incorporate wood chips down into the soil or into your backfill dirt.  Wood will tie up nitrogen for a year or two until it decomposes.  But if you leave it on the surface, the only interface between the mulch and the soil is that quarter-inch where the two meet.  If you simply lay them on the surface, the chips will not tie up nitrogen, and will become the perfect medium for fungal growth.  The more healthy your soil becomes, the quicker you'll find that the mulch disappears.  Fungi, worms, and bacteria all feast on the surface carbon and all do their part to pull it down into the soil profile.

As for punching holes vertically down into the soil, that would make some sense, I suppose.  If there is a clear tap root, I'll dig a narrow hole straight down and try to train the tap root to go straight down.  But with potted trees, you often will not find a single tap root the way you'll find that with a bare-root tree.  I would caution you from digging way deep (like 2 or 3 feet) to loosen up the soil directly below the root ball.  The concern would be that it will settle and then your tree will be an inch or two too low.  I wouldn't bother doing this with a fig tree --- they have a mass of small hairlike roots that take over the world.  

You can plant citrus close to a wall or sidewalk -- they aren't invasive.  Figs need more space.  Plant them too close to a sidewalk and you'll be sorry.

All plants have a natural ratio of root to shoot: that is, they will only grow leaves and branches in ratio to the root mass below the soil.  More roots, more shoots.  If you prune the branches, plants will actually sluff-off root mass (which is what happens when ruminants graze grass).   So even a potted tree with tightly bound roots will probably have a healthy root to shoot ratio.  If you hit your tree with a bunch of nitrogen in the first 6 months, you can throw this ratio off.  Suddenly you'll have all this green growth above ground while the root ball isn't sufficiently strong enough to support it.

Ask me how I know this: I killed an almond tree this way recently --- it over shot it's capacity to deal with hot sun.

The best fertilizer for young trees is pee.  Don't pee directly on the trunk, but outwards from the drip-line.  It's not too hot and will not burn the roots.  If you have a person in your life who wouldn't mind taking a leak out around the trees once a week or so, that'll be all the N-K-P they'll need.  

Invite me over for a glass of lemonaid in 3 years!  Or better yet, a slice of keylime pie.

Alicia said "doesn't seem like it would be very efficient to put in a fence around each tree and I would rather not put in a large fence in the area where I would like to plant my trees."

In my case I had gobs of 4' fencing on my property and t-posts sitting in a pile so it was free. There are posts about making a bone "sauce" that Sepp Holzer had made and brushed it on the trunks to keep deer away from fruit trees or any tree for that matter. Here's a link how to make to that.
https://permies.com/t/1805//critters/Sepp-Holzer-recipe-animals-trees

Jack, I will look more into the bone sauce that seems very interesting. I didn't mean to imply that it wouldn't be efficient in general, just that I don't have those materials on hand and it would be great to find another method of deterring deer and other critters if possible. I wish I had a supply like it you had!

Still coming up with a plan for an irrigation system and exact locations for the trees. I have a larger area for a fig and persimmon tree that would be getting some direct sun and some dappled sun. I know full sun would be preferred but I just don't have a large enough space with full sun since I have lots of mature oaks on my property.

I have another space that would get full sun where I would have to plant trees more closely together. I'm thinking of some citrus trees for that area maybe lemon, lime and grapefruit to start. Has anyone had success planting citrus trees just 5 feet apart and keeping them pruned to be quite small? This area would be much closer to the road and my driveway so I want to make sure the roots would not damage either. I've read different things about pruning in the winter vs. the summer to keep the trees small but still producing. Can I mulch the citrus trees the same as fig and persimmon? I have read somewhere that mulching is not advised for citrus trees but I'm unsure if this is just traditional lore.

As far as wood chips go, any recommendations for whether or not a pretty constant supply of dead leaves would work? I have access to a TON of leaves very easily but I will have to do more research on where I can get wood chips in my area (it's pretty rural where I am).

I live on somewhat of a hill and recently the power company damaged the asphalt that blocks water from running down onto my property and a type of DG was put in its place. I am going to call and see specifically what kind of material it is but I can definitely dig it up easily. I was thinking of replacing the berm they created to stop water flow with a swale and creating a hugel mound behind that and then planting the citrus trees below. I suppose this would collect runoff water from the street so I wonder if I would need to plant specific filtering shrubs on the mound or if anything would work.

The more answers I get, the more questions I seem to have. I'm so appreciative for all of the suggestions already!

Planting in clay is mostly the same as planting fruit tree in other soils.

1) Wood Chip to promote soil life that then keeps the mineral bio-available. (woodchip+winecap, straw+oyster mushroom)
2) Biochar keeps mineral bio-available due to its structure, it also provides housing for microbes
3) Amend the soil with rockdust/azomite/minerals
4) Inoculate the plants when you plant them
5) Dig the hole at least 3ft wide and 3ft deep so that the immediate area is aerated (dig a million dollar hole for that $18 tree)
6) Dont amend the backfill soil so that the new roots are encourage to leave the "hole" to seek minerals vs becoming rootbound )
7) Surround the plant with alot of nitrogen fixers(dutch clover?) 75%-90% of a starting food forest should be N-fixers a mature one should at least be 25% N-fixers
Don't forget the other plants: onion family, mint/thyme family, and the carrot family, personally I should do some more dynamic accumulators.
9) water flow/earthworks  raised bed/mounds/hugelkulture works very well in swampy are. (dont plant a tree on top of shrinking/decomposing hugelkulture), A swale might pool water during a rain and thus keep the plant "dry" and also store water for the plant in the dry season

I have about a foot of very acid clay on top of a hard pan of pottery like clay. Down there somewhere is a sheet of shale. My neighbor next door just built a house so I have some idea what's down there. When I plant a tree I mix a couple bags of sand, a lot of peat and some mushroom manure. On the next one I'll score the edges of the hole. I put in a new veggie garden last year between two fruit trees. I did that with the whole plot, except that around the edges I dug out a trench a spade wide and double deep and disposed of the hard pan. With amendments the soil level came back to where it was. I think of it as a raised bed in the ground. This was intended as a temporary veggie garden with permanent soil improvement for the fruit trees

But before I plant anything I drive in posts and fence it in. For a fruit tree I use one post and 5 foot high fencing. The neighborhood is mixed suburbia with wooded hillsides. Hunting isn't allowed, except with a bow. The last few years no one is hunting at all. So anything you plant becomes a deer treat. $35 plus shipping and it'd be gone the first night. Use a deer repellent and it'll last till the next unexpected rain.

I've been looking at apple root stocks and mm111 looks good for growing in clay and it doesn't need as much staking. But it grows 80% of the height of a full size tree. I need one maybe half height that's good in clay. But the ones I've planted ( semi dwarfs ) are doing well.

John Duda wrote:I have about a foot of very acid clay on top of a hard pan of pottery like clay.

Are you sure about this?  Generally clay is alkaline, not acidic, with a pH of 8.5 or more.  That is why organic mulches are so critical with clay soil—over time they lower the pH.

If you've ever spent an afternoon digging in clay soil with your hands, or have thrown pottery on a potter's wheel, your skin can attest to the alkaline pH of clay—it sucks the oils right out of your skin and excessively drys your hands out.  

The pH of clay soil depends on your climate.  
In drier areas evaporation is more than or equal to rainfall and so the minerals and salts in the soil move up to the surface and even create a white crust.
In wetter areas the rainfall is "too much" and all the mineral gets dissolved and make it to the water table that is only a few feet from the surface, then get washed out to the river/sea. This "rinsed out soil, now ends up with alot less minerals and salt, thus low pH aka acidic