Clay soil is really OK

I know a lot of people that enjoy gardening from time to time and they all say “I hate our clay soil!  it’s impossible.” Yes. Clay soil can be a complete pain in the ass to work with. But, I liken it to those who have thin hair and those who have thick hair — each person wants what they don’t have. Sandy soils drain well, warm up faster in the spring, and are easier to dig. But sandy soil also, has a hard time retaining moisture, doesn’t aggregate well (bind together in nice crumbs), nor is it nutrient rich. Clay soil is the exact opposite. It’s difficult to dig, drains poorly (as you have probably found that the soil stays wet for a long time and puddles when it rains), and it compacts as soon as you reach for any kind of garden implement. So what’s best? It really depends on what you are doing and trying to grow. Many CA natives and mediterranean plants will perform better in a sandy soil. But if I’m growing vegetables or annuals, I’d take a clay soil any day over a sandy one. Why?

It really just comes down to two things: nutrients and water. Annuals and vegetables perform a lot of work in one season. They have to grow fast, make flowers, and set seed so they can reproduce. All of this work takes a lot of nutrients and moisture. Clay soil can hold so much more water and plant nutrients than a sandy soil it’s almost unfair.

There’s a great amount of science underneath it all and I am by no means a soil scientist. I do have a decent understanding of the processes at work and I find it fascinating. I took a wonderful soils class a couple years ago at Merritt College in Oakland, I have read up on the subject, and have performed some of my own experiments over the years. I will explain it as I know and understand.

Particle sizes

Particle shape and size is directly related to the total surface area of a given soil volume

If you have ever taken a pottery class, the first thing you do with the clay before you actually make something is ‘wedge’ it, or knead it a bunch of times, to get the flat particles to align with each other. This work compacts the clay and makes it denser and stronger (absolutely not what we want in a garden but true to the point). Individual clay soil particles are very tiny and shaped like thin, flat, sheets. Since clay particles are small and flat in shape, clay soils have a tremendous amount of surface area and places where charged particles can reside. Sand particles, on the other hand, don’t really compact, are larger, and spherical in shape. So, for any given volume of soil, a sandy soil will have less particle surface area than a clay soil. I think it helps to think of two large bowls. Imagine that one is filled with marbles and that the other is filled with fish food flakes. The total combined surface area of all the flakes (if you laid them out end to end) would be much greater than the total surface area of the marbles.


The total surface area of the soil particles is related to the number of Cation Exchange Sites (places where nutrients can be held on the particles)

The surfaces of the soil particles are charged based on their molecular components (chemistry here — think of electrons and attraction) and contain cation exchange sites. These sites attract and accept nutrient molecules. You can read more about CEC (Cation Exchange Capacity) but what is important here, is that clay has a tremendous amount of cation exchange sites compared to sand. Charged nutrient molecules in the soil solution (such as nitrate, phosphorus, and potassium) become attracted and bound to these sites to be later taken up by plant roots. More sites means more nutrient holding capacity and ultimately more stored plant nutrients in the soil.


Lots of smaller air channels (micropores) can collectively hold more water than a few larger ones

Holding water is another thing that clay does well. There are three forces that we care about acting on water in the soil profile; gravity, adhesion, and cohesion. Gravitational forces are what causes water to fall toward the center of the earth, (the same forces that makes us stick to the ground). Adhesive force is the attraction of water to the soil particles (like water beads stuck to your shower door). And then there is cohesive force, which is the ability of water to molecularly bind with itself and can be seen when water beads up or pools together.

If we think back to the bowls of flakes and marbles try and imagine what the spaces around the corresponding particles looks like. There are many more and much smaller spaces around and between the fish food flakes. Whereas the marbles have fewer and much larger spaces between them. The spaces between the marbles will lose a lot of water due to gravitational force (water will fall through the marbles) and less will stick around because the surface area is smaller. With clay soils, the greater surface area means more more water will adhere. And rather than falling through the soil, water will actually be pulled along through the small channels via capillary action. This results in more water being retained per a given volume of soil.

So generally, if you hear that a soil is clayey it means it has the ability to hold lots of nutrients and lots of water… perfect for vegetables. A well amended clay soil (amended with lots of compost) can’t really be beat for tomatoes. And if it happens to be insanely compacted — well, then there are always mud pies.

Growing CA Natives on Residential Sites

Before converting a long hillside in my backyard to native plants, I excitedly researched and ultimately followed the main stream advice I was given… even though it didn’t feel right.  I then believed that you should not have to amend or add to your existing soil when planting natives.  Instead, plant species that are suited for your site.  So I set about planting natives that were noted for performing well in clay, given they have drainage.  In my case, this meant a slope, as water would flow more quickly down hill.  I planted clay tolerant varieties of manzanita, ceanothus, philadelphus, rhamnus (coffeeberry), verbena, and redbud. In the end, my results were about 20% loss, 60% struggle, and 20% so-so.  Obviously, this wasn’t what I was hoping for.

After watching my plants sit and struggle for about a year and a half I decided to test the drainage theory.  I took two coastal buckwheats and two deer grass plants as my subjects.  I planted one of each in the existing subsoil and on raised mounds about 6″ high.  The results were incredible.  The deer grass and buckwheat that were raised, more than doubled in size within the season.  The others barely grew at all. Since then, I have been experimenting with various mixes of gravels, soil, compost, and my native clay.  I rarely see plants struggle now that I take drainage seriously.  I also remain smart about which plants I choose, always choosing plants that can tolerate clay, because ultimately, that is what they are getting.  So, here follows my advice for succeeding the first time around with plants that need good drainage.

If your soil drains well, and it has some good topsoil (like maybe you are converting a lawn that was previously doing OK) then you might not need to do much.  Especially if you plan to sheet mulch it (layer cardboard, compost, and mulch on top to smother the lawn).  You will be providing drainage and enough nutrient to last a long, long time.

Here’s a quick way to check your soil for adequate drainage. Dig a hole about 12″ deep by 12″ wide, fill it with water and see how long it takes to drain out. If it drains completely in 2 hours you don’t have anything to worry about. If it is there for most of the day or longer then you should do something about it. And don’t listen to anyone who tells you what to do without asking you what your soil is like.  My situation was a pure subsoil that had been driven over by all things machine,  blown clear of its topsoil, and nutritionally depleted by tree and shrub roots.  Even weeds had trouble growing there.  So….What is your soil like? (here I will be referring to my specific situation, yours may be completely different)

If your soil drains very poorly to poorly, like mine, I recommend you amend it to get good results.  First, break it up with a pick axe, an auger, or a rototiller and add compost and pumice.  It is important to treat the whole area where you are going to plant and aim for a working depth of 12 – 18″ deep, but sometimes this isn’t possible or practical.  The deeper you go the better the results you will get (especially for large shrubs and trees) but I have had good success roughly pick axing down 6″ and mounding above my clay soil with 6″ of a faster draining mix.  I recommend to my clients a blend of soil that is 25% lava rock, pumice, or light gravel, 25% compost, and 50% loam or topsoil.  This aerated mix will allow oxygen to exist around the root zone which the roots need to respire.  Lots of natives have trouble with Phytophthera root rot and amending for drainage in the upper portion of the root zone is a great way to prevent it from getting ahold of your plants.  Add a good organic mulch (like wood chips from a tree service) and the organisms will do more even more aeration work for you.

Growing natives in residential yards is a relatively new thing, having these plants commercially available is also relatively new.  Houses are built on compacted lots in urban and suburban areas and we don’t have undisturbed, living, native soil.  We have sites that have been plowed clear of the topsoil when the foundations are dug, and rode over countless times with bulldozers and tractors.  The native vegetation and organisms have been removed, the soil ecosystem is destroyed, oxygen is removed from the soil, and the critical topsoil has been removed.  If someone wants to grow native plants, this type of situation should be viewed more like a reclamation effort rather than a weekend gardening project.  Compacted, flat clay is one of the worst soils for growing many drought tolerant plants and CA natives.  But, if you amend for drainage you will open your options up ten fold with plant selections.  If you can’t dig down much it’s still OK.  Mound up at least 6 inches with a draining soil and mulch well. Organisms will do the rest, it just takes time.  But in the meantime, your plants’ crowns will be in a soil that drains well and that will help considerably.

Dry farming tomatoes in summer dry climates

It’s my favorite time of year — summer vegetable planting time. Every year I try some new things out. Some are intentional and others are by accident, and last year there was a fabulous dry farming event that I intend to duplicate. My mom first told me about dry farming several years ago. She had read an article about a guy who grew his tomatoes that way and he said that they were the best tasting tomatoes ever. He said that all the sugars get concentrated and the plant is stressed a little so it puts a great amount of effort into reproduction (fruit production).  I thought it was a great idea and now I know it’s one.  Last year when I was out getting my beds ready in February, I noticed there was a tomato seedling that came up near my compost pile in part of my garden where I don’t have irrigation. I let it go thinking that it would get hit with a frost, but it had a different plan.  April came and then May and June. The plant was huge and extremely healthy. It was also loaded with tomatoes. In late July they began to ripen and they were out of this world tasty. Incredibly sweet.  It was a Juliet tomato.  Juliet is an early producing indeterminate plant, so it should have produced all season, but this one really seemed to have one massive flush of tomatoes, I’m guessing around 200-250, but that’s not bad considering I never watered it. Not once. I also wasn’t very thorough about picking the tomatoes because a lot of them were in a tangle on the ground and my son rode over the plant a few times while on route a top his big wheel.  It was a bit of a mess, but the fruit quality was incomparable. It was left to scramble on the ground, it never asked for anything… it just gave. I am assuming that getting the early seed start that it did, and the fact that it had a compost pile (also unwatered) nearby really helped it root deeply and retain moisture.

This year I am trying it on purpose.  My plan: plant a seed grown tomato, one that is an early producer, right after the heavy spring rains (when the soil is thoroughly soaked). Tomatoes can reportedly send roots down 8 feet.  I’m going to let the seedling get a little leggy (withhold a little light) and plant it as deep as possible (all the way up to the last set of leaves).  I’m going to put it on the west side of my house where the ground is shady for part of the day but the leaves and upper part of the plant will be in full sun. I’m also going to mulch it like crazy.  Not inches — feet. Every time I get tempted to water it, I’m going to add more mulch instead.  I’ve got a few seedlings of the same variety so I’m going to grow one as I normally would for a control.  I realize 1 test and 1 control doesn’t make much of an experiment, but hey….I’m a gardener now, I’ll leave the hardcore science to the hardcore scientists.


Quick update: I planted this little guy today. I watered him after doing so, about a gallon. But that’s all he gets. He has a mulch volcano all around him of lawn clippings leaves and pine needles that’s about 8 inches tall and as wide (I plan on adding to it as soon as possible). A little worm came out as I drenched the soil… I’ll take that as good luck. It should probably be noted that I didn’t do much hardening off because the weather is going to be super warm and this might be the last of the rain this year. He’s planted up to his neck and yep, I left the seed leaves on as this guy wasn’t as leggy as I was aiming for.


A 2 week old Favorita seedling planted in a heavy clay soil amended with compost and oak leaf mold.


October 24, 2016: I realize that it is very late to be posting this update. But as planned, I did not water this plant once all year. I ended up mulching it with about 18″ of leaves and grass clippings and random bits of yard waste. Here’s what it looks like now.



So did it work? I’d say so. It did have a couple weeks in the early part of the dry season where it got a little ragged looking, but then it found what it needed and took off. It made a lot of tomatoes and the ones that ripened were awesome,  but…. I grew it in too much shade and they never ripened well. : (  I will be doing this again next year in full sun. Clearly tomatoes don’t need as much as much water as we think they do.  Just for reference and scale, the wheelbarrow in the background of this picture is my son’s (child size). The plant is 6′ in diameter and about 3′ tall.

Landscape contractors: 5 things to look out for

If you are looking to hire a landscape contractor, or other laborers to perform work on your property I have a short list of things that are commonly overlooked.  I think these things are essential to anyone having work performed,  but it seems these things happen again and again from my observation. I would recommend that when you are getting bids for work performed that you go over these items and make sure that they are addressed.

  • Work should not be performed when soil is saturated

This is one of those things that should be a no-brainer, but it happens a lot.  The other day I was driving into town and passed a house that was having a planting design installed.  It was pouring rain and it had been raining heavily the past 2 days.  A crew of 5-6 men were working with wheelbarrows and shovels digging and hauling, all over the front yard.  This leads to a tremendous amount of compaction that could have been completely avoided by waiting for the soil to dry out a little.  Sometimes it can take days for clay soil to dry out enough for heavy working.  But if it were my yard or my client, I’d insist the contractors wait a couple days.  Sandy soils dry out faster and can be worked sooner than clay after rains, but it is still a good idea to wait a day or two after heavy rains, and certainly not be working while it’s raining.

  • Irrigation should be installed for the size of the mature plant

Again, a no-brainer… but it isn’t.  Landscape contractors typically only put in a single drip emitter or maybe 2 around a new plant.  What about when this plant gets large? There are a couple ways to address this issue depending on your soil type but just double check with them that when your 1 gallon shrub turns into an 8’x 8’foot bush the drip emitters can be adjusted in a way to compensate for the mature size of the plant. My preference is to use a 1/4″ valve with 1-2 emitters before it and 1-2 emitters after.  Start with the valve closed for in the beginning and then when the plant doubles in size, open the valve and move the emitters farther out to accommodate the larger plant and have water reach the edge of the root zone.

  • Rocks should be buried in the landscape

It’s not very common to see rocks just plopped on top of the landscape.  Usually soil has eroded away and revealed the rock underneath or water has washed over it and deposited gravel at its base in the case of seasonal creeks.  They look like they fell from the sky when they are just plopped on, or actually if they had fallen from the sky they would also be partially buried on impact.  Have your contractor bury them at least 1/3 into the soil and group them in natural arrangements.  A good designer or contractor that cares about their craft will be able to achieve a nice esthetic.

  • Plants are installed in a watering well

A lot of installers think that it conserves water to build a watering well around the base of a tree or shrub, or even newly installed perennial.  I do this when I know I am coming back or inform the homeowner about what to do after the hot season ends.  So the reason for doing this is that when a newly installed plant is becoming established, it is really surviving on the root ball and it can take a long while before roots go out and down to seek nourishment and water in its new environment.  A water well helps direct and conserve water near the root ball where the plants need it.  It’s a good idea as long as you keep an eye on this and know that when the rainy season begins, these berms need to be broken down.  Sometimes I see plants and trees installed below grade which is almost never a good idea unless you are planting something whose native habitat is a vernal pool.

  • Plants are installed too close together

This is a tough one because I know that people love to see mature landscapes. Healthy landscapes are constantly evolving, they are not static.  Some plants will mature and die and will need to be replaced, others need to be planted from when they are very small in order to get good establishment.  A newly planted landscape offers a lot of opportunities, to tuck in vegetables, herbs, containers, and annual flowers that will grow quickly and fill the spaces, later as plants mature these additions won’t be necessary.  It’s important to allow for the mature size of the plant otherwise when they grow up, they look cramped, need excessive pruning, shade each other out and don’t look healthy, etc.  If you ask for plants to be moved closer a good contractor will tell you no : )

A beautiful landscape really does add value to your home.  It should be thought of as an investment.  If you are taking the time and or spending the money to have something done for your property make sure you are getting it done right and that it’s going to last. The first house we sold went way over the asking price.  I don’t know for sure if our yard had anything to do with it, but we got over 30 letters when the bids came in and about half of them mentioned how much they loved the gardens in the back of our house.  I don’t think a bad yard hurts the value of a great house, but a great yard can send a good house over the top.

Recycled water in home landscapes

The trouble with reclaimed water

Last year during the summer I saw a lot of trucks hauling reclaimed water from the local water treatment plant. Free water! = great idea! = not so much? = maybe even no.  I have to admit, I had never thought of using reclaimed water in my landscape.  I prefer the good stuff from up above, and don’t need that much of it anymore. Plus, hauling a big tank around doesn’t seem ideal for a long term plan.  Then a friend of mine reminded me that it has a lot of salt.  Yikes!  If you need to use it to get by on the short term here’s what I would do:

  1. know your plants and whether or not they are salt sensitive
  2. ask the treatment plant if they have done any analyses on it
  3. get it tested yourself so you know what you are dealing with
  4. water very DEEPLY and less often

Deep watering is a must

Salts move through the soil along with the wetting front. That means if you water shallowly (not past the root zone) salts will accumulate in the soil as far as the water reaches. If this is in or near the root zone, it can stress the plant.  A lot of people who think they have a brown thumb when it comes to indoor house plants, often water their plants too shallowly and never flush the soil thoroughly so that the water runs out the bottom of the pot.  After a couple months the leaf tips start to turn brown. This is because the salts in the fertilizers never get moved out and the salts in the water (tap water has salts too) you are applying accumulate, compounding the problem.  The same principle applies to plants in ground, water really needs to move past the roots to encourage deep rooting and flush out contaminants like salt.  How do you know if you have watered deeply enough?  In compacted clay soil (which is what is very common in the east bay) water tends to move out first, rather than move down.  Watering slowly promotes better saturation at good depths.  The only way to know is to dig down near the plant after watering and check or you can use a moisture meter.

Gypsum is usually helpful

If someone tells you to add gypsum to your soil to alleviate the salt it ‘might’ be a good idea.  When you add gypsum to a soil it does two important things. First, the calcium in the gypsum replaces a lot of the sodium ions on the cation exchange sites.  Second, the sulfate in the gypsum binds with the sodium to form sodium sulfate. Sodium sulfate is highly water soluble and it can be easily flushed from the soil.  The importance of this is that these reactions work with sodium, but not all salts are sodium salts.  There are others such as magnesium, potassium, and boron. You can’t know what is in the water unless you ask or get it tested.  Using too much gypsum could adversely affect your soil by creating a calcium / magnesium imbalance.

Is using it okay?

In general, I think it’s okay to use reclaimed water on salt tolerant plants if you water deeply.  I’d also back off on the fertilizer if you use it.  If you notice your plants or trees are declining, get your soil tested. It’s so easy to do. For $35.00 you can get a ton of information that a good lab or gardener can interpret for you.

Colored mulches aren’t the best

The benefits of mulch

There are a ton of wonderful benefits that mulch provides for a landscape such as water retention, improved water infiltration, temperature moderation, compaction reduction, and erosion control. Two other key benefits, ones that are often hard to see unless you are digging for them, are the food source and aeration that it provides to the soil environment. Mulch alone can actually bring a mostly dead soil back to life. The one caveat though, is that it needs to be a mulch that actually decomposes into the soil.

Mulch in action, a real application

I have an upward slope at the back of my property that is about 12 feet in depth and it runs the entire length of my backyard.  The previous owners had a yard maintenance crew that walked along the hill and blew around dyed mulch, leaves, and topsoil every week  (not much help there, but that’s another story).  I was left with scattered patches of faded mulch, bald clay spots and hybrid-t roses that weren’t doing well. Before planting my design, I pulled the roses, and removed all of the existing mulch.  There was no topsoil beneath the mulch; there was no topsoil anywhere.  I was working with heavily compacted, anaerobic clay loaded with large rocks.  I used a pick-axe to make 25 holes for shrubs and trees; I never saw a single earthworm, grub, or viable insect.  Organic and natural gardeners know this is not a good sign.  After planting,  I topped the soil with 5″ of wood chips from a tree service and let things go.  I lost a few plants (not surprising) and I learned a lot along the way about how to make a graded residential lot suitable for growing natives (keep an eye out for an upcoming post about Mediterranean plants on standard residential sites).  But what was most surprising to me was what happened to the soil just one year later.  When I was digging around the following season to check on my plants, I dug under the mulch and found all kinds of life, earthworms, beetles, and lots of little crawly things.  Underneath the mulch it was cool and moist where it touched the existing soil and it was beginning to decompose, feeding the soil below.  A new topsoil was being created and it smelled healthy and earthy.  Roots and rhizomes from my plants were occupying part of the I/O layer (the inorganic / organic layer of soil, where soil meets organic matter) and worms and beetles were burrowing between the two layers creating much needed air spaces.  There was life in a once lifeless environment.

Toxicity and the issues with colored mulches

There are a couple other potential issues with these kinds of mulches.  Sometimes they are made from chipped pallets or recycled wood from construction waste.  Some of these woods could have been treated with various chemicals like chromated copper arsenate (CCA). In addition the dyes and chemicals that are used to color the wood should be checked as well. I know some of the black chips are treated with carbon black (which is basically charcoal) and the reds sometimes are made from iron oxide (rust).  As far as safety goes, these are fine to add to the soil but the iron dioxide may stain concrete. If you are going to use these mulches I’d definitely check the source and verify that they are free from chemicals that will adversely affect your soil.  Here’s a quick and informative read on the topic from the University of Massachusetts about the potential toxicity in these products:


The soil under my mulch after 1 year. It’s hard to see, but there’s an earthworm in the circle.

The differences in mulches

What can we take away from this? Wood chips decompose and provide soil and plants with many healthy benefits that dyed chips and inorganic mulches do not. Think of natural mulch as a very slow acting compost. Rubber mulch and the dyed wood chip mulch that’s usually seen in black, red, and brown colors doesn’t decompose (at least not in our lifetime). These products are not natural and lack the most important benefit that mulch has to offer: a long term food source for your plants and soil. These aren’t my opinions, they are observable facts. My opinions on dyed mulches are also not very favorable…

If you don’t like the rustic look of natural wood chips…

I understand the attraction to dyed mulch, my husband likes it because it has a uniform color and provides a good contrast to plants…. But to me it looks much worse whenever anything foreign (leaves, twigs, flower petals, weeds) drop on or grow through it. It also fades out in about 2 years and looses its initial appeal. If you want to have a more uniform look in your planting beds, I highly suggest buying  natural bark mulches, or screening your own tree chips (if you don’t mind the extra work). You can always put down an initial layer of tree chips first (ask the tree company for chips from healthy trees, a good company will know when it’s pulling and chipping trees that are diseased and will not want to pass that on to you, if you are only doing a small area then I’d look at getting bags of a partially decomposed forest bark, redwood soil conditioner, leaves from your yard or leaves mixed with grass clippings  — something that will decompose in a year or two, but not as fast as compost so you are feeding the soil at different intervals ) Then top with a 3″ layer of fir or redwood bark. Bark has a lot of natural resins and waxes that prohibit rapid decomposition so it will last longer than natural wood chips and keep its color for several years, but it will eventually feed the soil faster than the dyed mulches. With this approach you will get looks and function.

Vegetables make flowers too

I went out to pick some broccoli last night thinking I’d be able to add it to my stir fry… too late. The unusually sunny and warm weather we have had the past two weeks sent my already twice harvested broccoli plants into reproduction mode. The sugar snap peas were looking good but starting to flop over since I was lazy about trellising them this year (I couldn’t decide if I wanted them for a cover crop or eating). I started snipping off the broccoli flowers thinking I might be able to get them to go again, but they were too far gone to reproduce anything but flowers at this point. I looked down at the bunch in my hand and thinking about farmgirl flowers, I came up with another idea which lead to a bit of happiness instead of disappointment about my stir fry…