Planting in Clay Soil

Cayos Cochinos, Honduras(Zone 11)

I want to plant some rosemary on a patio where we dry laundry. Unfortunately, the ground is a bright red clay soil. I was wondering if I could dig out a hole holding the same volume of soil as a large pot, put good soil in, and sow the seeds? Any ideas?

Charlotte, NC(Zone 7b)

RioGTomlin - Unfortunately this will probably not work. When you dig a hole in hard red clay, you have created a hole that does not drain well. Even if you fill it with good soil, it still will not drain well.

I have Rosemary growing in a ten gallon pot sitting on the clay soil, and it does very well. I have never had much luck growing Rosemary from seed. Your local nursery should have small Rosemary plants at a reasonable price you could transplant.

Cayos Cochinos, Honduras(Zone 11)

Thanks Honeybee. My mama said it's very hard from seed as well. But, seeds are what I have. I will have to try lots of them in a large pot placed on the patio.

I live on a small island with no roads, stores, bikes- population 50. No nursery here! Even on the mainland, the nursery in La Ceiba only has local palms, elephant ears, flowers, and a few conifers. There is another about an hour away called Curla that sells grafted tropical fruit trees, but I'm on my own with herbs.

Any tips for Rosemary from seeds?

Charlotte, NC(Zone 7b)

RioGTomlin - I never had luck growing Parsley from seeds when I sowed several in one pot. This year, I put one seed in each very small pot and most of them grew.

I suspect some seeds don't like competition.

Try sowing one seed in two inch pots - not too deep. I hope this works for you.

Rosemary is easy to grow from cuttings - maybe a neighbor has a sprig they can let you have.

Cayos Cochinos, Honduras(Zone 11)

I can try that with the parsley, we start most plants in biodegradable egg cartons. Unfortunately, I already used all my seeds! DOH!

North Ridgeville, OH(Zone 5b)

Can you build a raised bed on top of your clay?

Cayos Cochinos, Honduras(Zone 11)

Yes. That is what I have done already, running the length of the area. I have basil, cilantro, parsley, and chives in there. I could try putting the rosemary at the far end, but it would get the least sun of the whole bed.

Charlotte, NC(Zone 7b)

RioGTomlin - You might try Rosemary at the end of you raised bed to see if it will do okay, even though it might not get full sun. I've always grown it in full sun.

When I lived in South Florida, I had a Rosemary bush that grew taller than I am!

Everett, WA(Zone 8a)

If the slope is right, you might try cutting a little trench leading downhill and away from the clay under your raised bed. Water that drains down out of the raised bed is bound to have some organic matter and nutrients.

If some of that seepage can perk down into the clay, then down and out through your trench, the clay that it passes through is likely to soften and be enriched over time.

As long as drainage keeps the water draining away so it doesn't 'drown', worms and roots and bugs should eventually break it up and turn it into soil.

That would make your raised bed that much deeper, and all you have to do is lower the water table under the clay by cutting a trench!


Cayos Cochinos, Honduras(Zone 11)

That's an excellent idea Corey. If I'm understanding correctly, the trench would be facing downhill, so water would be moving if it could not be absorbed. Would this trench then be filled with the same soil as the raised bed? I understand the idea, but can't quite picture the design.

For larger areas we have on a slope, I'm planning on making rows of small trees and shrubs by digging out a trench and filling it with good soil. Then adding compost mulch to build up the nutrients along the row. I would like to have this gradually develop a more terraced slope, and by adding enough mulch from compost and created by the trees/shrubs themselves, the then terraced soil would be at least loose enough to turn, and maybe become more fertile. I hope.

Everett, WA(Zone 8a)

>> by adding enough mulch from compost and created by the trees/shrubs themselves, the then terraced soil would be at least loose enough to turn, and maybe become more fertile.

That sounds like a really good long-term plan. encouarge something to grow ENOUGH that it enriches the soil, which then lets it grow well.

>> If I'm understanding correctly, the trench would be facing downhill, so water would be moving if it could not be absorbed. Would this trench then be filled with the same soil as the raised bed?

I'm not ambitious, so I use the easiest method that improves one bed enough to thrive. I just start a trench from whatever corner or edge of the raised bed's "floor" that is lowest. When I'm building the raised bed, I do dig down at least a little, and "slope" the hard clay floor down towards one corner. Sometimes I even cut little channels into the floor, as wide as the scrpaing mattock's balde (2") I figure the looser soil in the bed will drain down TOO the clay floor, then along that floor or those channels down to the low point.

If I didn't do anything else, the water would pool at that point, drowning and killing roots every time it rained or I watered heavily.

So I dig a trench down and away from the low point of the bed's floor.

Basically, I draw the shortest line that reaches a spot lower than my bed's floor (assuming THAT spot also has some kind of drianage to prevent a mud puddle at that point.

In practice, I have a bigger trench that runs along my driveway, that is lower than the rest of that part of the yard. So allk the little RBs in my yard can be drianed down to my main driveway-trench.

So I'm saying that I just cut little trenches, as short as possible, straight downhill, the way a soccer ball would roll if I dropped it at the low corner of my RB.

But a real landscaper would say this is lazy, wrong and inefficient. A trench that goes straight downhill really only drains one "point" at the top of that trench.

If I were ambitious, or had a team of strudy young men digging for me, I would SLANT my trenches ACCROSS the slope of the yard, so they ran downhill, but also sideways. They would forma kind of herringbone pattern accfross the whole yard.

That way, they would drain the whole yard, lower the whole water table there by sverral inches, and benefit everything in the yard, not just the RBs.

Imagine unwanted water as a battalian of troops, marching in waves down from the highest part of your yard towards the lowest parts. Since the clay doesn;t drain, they drown anything in their path, like troops trmapling plants underfoot.

Trench that run straight downhill would only divert a few of the troops. Any in-betweem trenches would keep marching down, causing eroison and high water tables.

But if a SERIES of trenchs ran along the hill, slanting doiwnwards gradually, any given soldior would only march a few feet, until he reaced a trench, turned to follow it downhill, and was carried away safely.

Slanting trenches DIVERT run-off. The water table of the wyhole yard would lower, letting air into the soil to that depth everywhere. Now roots and worms and dissolving compost can penetrate to that depth and soften the soil.


Everett, WA(Zone 8a)

>> Would this trench then be filled with the same soil as the raised bed?

I think it mostly depends how much rain you have, how much money you have, and how big your muscles are.

1. "tiling"
Dig huge, deep trenches. Lay pipe in the bottom. (Perforated corrugated plactic, or 'tile' pipes.)
Surround the pipe with gravel or crushed rock.
Maybe surround that or top that off with filter cloth.
lay a thin layer of soil on top.
(I hope you have power equipment, to dig with and to haul in crushed stone.)
(This is the Army Corp of Engineers solution, like digging the Panama Canal.)

You could screen what you dig out, and use any rocks you find to backfill with.

2. "French Drain"
Dig a pretty deep, wide trench.
Probably lay some filter cloth down so it doesn't silt up fast.
Lay down 3-4" of gravel or crushed rock.
Fold the filter cloth over that to keep out fine stuff.
Lay a few inches of soil on top.

You want gravel in the bottom so it drains fast.

Filling it with soil, even amended soil that drains failry well, makes it likely that as roots and clay perk back in, it will "silt up" and not drain well. If it doesn't drain fast, the wqater that comes in from the top and sides will dwell there, excluding air and killing roots or soil microbes.

If you filled it with REALLY well-draining mix, like coarse sand, that might work well, but be sure to keep clay and silt out, or it will plug up tight.

3. Lazy Corey slit trench (or small-scale quick-fix)

Cut a narrow trench, the width of a mattock-blade or hoe.
Don't cut it any deeper than you need to ... but the floor must be downhill at all points.

In theory, stretch a string from the btoom of the low point you are draining TO, up to the bed you are draining FROM, and dig down to that level so you have some slope at every point, but dig no more than necessary.

If you don't mind breaking your ankle every so often, or catching the lawn mower wheels in it, you could be done right now. Grass will hide the little trench, and you can't silt up an open trench. If it does, scrape that ooze out with a hoe and put it somewhere you want silt.

This takes advanatge of that industrial-strnegth clay we both have. The sides of the trench are so hard and firm they will last for years, and you can make it like new by dragging a hoe or mattock along it, easy-lazy-fast.

If the clay improoves to the point where roots start growing out of the walls so fast they clog the trench, congratulations! At that point, maybe convert it to a French Drain.

If you don't like guests breaking thier ankles or tripping over this open mini-slit-trench, treat ot like a mini-French Drain. Couple layers of filter cloth, some gravel, cover, cover that with soil. But make it as small and shallow as possible, so you don't go broke buying gravel, or break your back hauling dozens of bags of gravel!


Everett, WA(Zone 8a)

Over in the Container garden forum, Tapla (Al) describes how pots and planters may hold more water than you might expect, calling it "perched water". If your raised bed has a rock floor, or a layer of plastic, or TOTALLY impervious clay under it, MAYBE it would act like a pot instead of like soil.

Usually the soil under a raised bed will allow SOME water to perk down through it, like a very slow wick. That would eliminate the "perched water layer" that might otherwise dorwn roots in a container or sealed raised bed.

Unreasonably assuming zero drainage DOWN, I want to be sure my bed drains sideways into my trench. So I might run some kind of wick - cotton or rayon fabric, or a few strands of "Wonder Mop" material - along the lowest point of the RB floor, DOWN into the trench, so those last few quarts of perched water were sure to drain down.

But I'm not actually that paranoid. I just want to mention that, technically, those inches from the amended soil in your bed through the air and down to your trench, have no capilary "pulling power" to drain water out of the bed.

If it matters, and you need every single inch or millimeter of amended soil to be well-drained for your roots, and if your clay is really like rock and amazingly 100.00% impervious to water, and it often rains hard, you MIGHT want to check the lowest part of your RB soil after a heavy rain, to make sure it drains fast enough to please you and your roots.

If not, let's talk wicks!


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