To be honest, 6.5 and 7.8 are really middling sorts of pH values. Pretty much neutral. I wouldn't call either really acid or alkaline. What are you trying to plant that would be super sensitive to pH?

Also, how are you testing your pH? Cheap, home electronic pH testers are notoriously unreliable.

I'm planting some tropical plants, which usually like the 6-6.5 range. I've spent a good bit of money on gardenias (likes 5.0-6.0) that never succeeded due to my pH being too high. Also have a few lemon trees who continually have yellow-ish leaves, and they like 5.5-6.5. So even though the pH isn't drastically off, I still see the effects. I thought that, with a new bed, this is the time to get it right, give the plants the best opportunity to succeed.

I'm using a $50 glass electrode pH meter that I used for home brew. Calibrated prior to doing the soil measurements, so I trust the readings.

Do you know why the soil in the box is pH 7.8? Where did you source that soil? What have you added to it?

Thanks Dan. So does high pH topsoil actually lose pH and transfer it to the lower levels? How long does this take? I'm just thinking about the situation where I have deep, high pH topsoil and young plants. If the alkalinity transfer isn't swift, I would think that I would still want to amend the soil slightly to knock down the pH of this upper layer.

I was a little surprised how little topsoil I had in some areas. In Houston, the solution to get away from the gumbo soil is to add more topsoil on top (raised bed), not dig out clay and add patches of good soil. Doing that creates what they call here the bathtub effect- the surrounding gumbo acts like a clay pot to hold in water around your plants The only way to provide well draining soil here is to add it on top of the clay, and then let the natural runoff occur between the topsoil/clay interface. Yep, much more difficult to grow plants than you would think for a place with a ton of rain and a ton of sun.

Hmm. That's a good point. If you dig a hole in clay, it's like you're in a clay pot. You're just manufacturing a puddle.

As to transfer, I guess it depends what is making the topsoil alkaline. Around here it's limestone. Caliche, to be precise. So if you apply water to the topsoil, it'll become alkaline, and it'll percolate below. Now, that's been happening for aeons in your soil with rainwater, so I have to assume that your gumbo remains slightly acidic because it is largely impermeable by water. Again, the clay pot effect. I guess that means that you're simply not going to change the pH of the gumbo.

To the extent the gumbo is largely impermeable to water, why are you worried about it at all? Roots won't easily penetrate it, will they?

Ridgerunner, the soil is a mix of topsoil/bedding soil from a nursery with additional compost added. The base of the soil and the type of compost, I do not know. Nothing else has been done to it however.

Dan, roots won't necessarily avoid gumbo soil, its just better that they do. For trees and large shrubs, Master Gardeners down here recommend you plant your tree/shrub directly into the gumbo soil with lots of root stimulator. Basically, the tree learns quickly to burrow through the clay or it dies. But for smaller plants, you try to avoid the gumbo just because it can create root rot.

Thats interesting, maybe you can't change gumbo soil pH, at least quickly. A It doesn't drain fast, but it will eventually drain, so it will eventually adjust its pH. And adding compost to the top will slowly amend the clay as well- maybe pH adjustments have to be done along with the addition or organic material to improve the drainage.

In clay soils you really can not lower the pH. Clay has buffering agents that have to be all burned up before it can lowered. It is much easier to raise pH than to lower it. It would take alot of sulfur and about 6 months to react, and even then it will tend to go back to the surrounding pH over time. The best thing would be to have taller beds and add the type of soil you want.

I would use ammonium sulfate rather than aluminum sulfate. Aluminum sulfate can cause problems with aluminum toxicity over time. I have the gumbo clay but its pH is about 5.5. I still use raised beds just for the additional internal drainage.

Soil will naturally acidify over time from the acidity of rain, nitrification of ammonium sources like synthetic fertilizers, manure and OM in combination with the leaching action of water passing through the soil. Acidification can be accelerated by adding amendments but they have their issues. Elemental sulfur, is a biological process, so it needs warm temperatures and moisture. Too much moisture and it can create toxic conditions if the soil becomes anaerobic. It can also take up to a year to fully work, delaying planting. Aluminum sulfate and ferric sulfate acidify through chemical reactions, so temperature isn't as critical and microbiology is not involved. They work much quicker than any other processes, but both aluminum and iron, especially aluminum, can become toxic to plants at higher levels.

I agree that trees should be planted in the native soil and not into a hole filled with "improved" soil. Otherwise they tend to become root bound.

Not clear about the mineral makeup of the OP's soil, but soil doesn't naturally acidify if it is a bed over limestone.

Excellent observation.

The 2 to 6" of mix of topsoil/bedding soil from a nursery with additional compost added will naturally acidify over time.

Op's gumbo is most likely sand, silt and clay as much of Eastern Texas soil is ancient Mississippi River deposits from a few major earthquakes ago. It is at pH 6.5 and isn't likely to change much or at least not quickly or easily as that is a characteristic of clay and subsoils in general.

On to your observation: The rest of Texas is calcareous soil. Meaning the soil has a high content of calcium carbonate/limestone. All the carbonate in the soil would need to be removed by acid for the soil to reach a pH of 7. Soil pH adjustment is either neutralizing acid with carbonate or removing carbonate by adding acid. A study found that the application of 10,000 pounds of sulfur to one acre of pH 8 soil only reduced the pH to 7.6 at the 7" layer. It's why no one in their right mind tries to lower the pH of limestone soils. The acidifying equivalent of 5 tons of sulfur would be a lot of rain and OM nitrification. The key qualifier in my acidifying soil comment is "over time." So even Western and Central Texas high pH soils, to a depth of 5-8" will eventually be naturally acidified, it will just take a couple hundred thousand years. :) But realistically? No. So good point.

If you want long term solution you may want to try mulching your gumbo soil with wood chips. This isn't something that will change over night but something to be done over years. The wood chips will keep the ground moist over longer periods of time. This will speed up the decomposition of the bottom layer of wood chips which will begin to add organic matter to your gumbo soil. I have read success stories of people that have a clay heavy soil transform it into loamy earthy soil.

How was the soil pH test done? Who did that soil pH test? A home kit from the local garden center? A good reliable soil test from Texas A & M?

What is the ratio of Calcium to Magnesium in each of the soils? That should be about 5 parts Ca. to 1 part Mg.

While the advice to build raised beds means the possibility of a quicker planting area the beds need to be much more than 2 to 6 inches high to allow proper drainage. Your clay soil can be made into a good planting soil if adequate amounts of organic material is added to that soil. While you will never transform a heavy clay soil into a loamy soil it can be made much better.

kimmq is kimmsr

Well, I thought I was in my right mind when I tried to acidify my limestone soil many years ago. Rather quickly found out that I wasn't. As I said my tap water is alkaline (because it come from lakes that are full of limestone silt), so whenever I water, which I do a LOT here in the summer, it defeats any acidifying amendment.

Now, as noted, one could gradually improve the soil tilth of the gumbo by adding organics, but that's not going to change the pH much. Unless you do it on a large scale, you're still going to end up with decent soil in an impermeable clay pan that won't drain.

It's looking like highly raised beds, or maybe containers.

But the pH does not have to be ideal if the soil has good organic matter and a healthy microbial population. In other words, plenty of compost will help a host of evils.

What others are saying about the raised bed soil being hard to acidify if it's limestone based is true. You could still try amending and see how it goes. Perhaps a mixture of fast acting (ammonium sulfate) and slow acting (sulfur) and see what happens. Adding enough to drop it a full point at once may be a lot - that's just my feeling. Maybe go for half a point and see what happens.

If you have a good calibrated meter with a glass electrode you're in business. I assume you're making a 50/50 slurry with distilled water to measure? That's the best way.

A few thoughts on growing over the clay: Roots will penetrate eventually. It helps if you break up the surface a bit before adding the other soil on top. Also, over time the soil food web + natural leaching will carry organic matter down into the clay and improve it passively. Worms - if you have them in that harsh environment - will come up to get the compost and make tunnels through the clay in the process. This helps aeration, root penetration and allows more stuff to percolate downward. This is my impression of the process after dealing with similar conditions in MO. Early tilling followed by occasional digging to plant vegetables eventually resulted in a foot of pretty good soil with the top third being the raised bed.

Andrew, I will admit that I misread your original post, thinking the higher pH was the gumbo clay. Your lemon tree will do fine in that raised bed, they will put roots into the clay and get the nutrients they need. The bedding material could have been raised by adding lime. It should not affect the gumbo clay. as the buffering affect also keeps the pH from going up too much as well. Bedding material is usually made up of sandy loam and will be easier to change the pH. Also, pH changes during the year. It also varies due to the moisture content of the soil.

Thanks for the responses guys. I'll try to answer a few questions from the previous posts.

I was testing pH using a decent meter and calibrated. I was using 1 part soil to 1 part distilled water, but then changed to 2 parts soil to 1 part water when I got to the clay soil, based on some recommendations I saw online (I needed more water to get the clay to break up). I was calibrating before each measurement, though I noticed that the clay soil seemed to throw my calibration off quite quickly.

The gumbo soil seems to have a lower pH than the new topsoil/compost.
That was a little unexpected, as many people seem to have gumbo soil in
the 7-8 pH range.

Some good comments about he nature of lime-based soils like gumbo, and the benefits of compost. Looks like another reason to raise beds higher and add mulch/compost frequently. The areas that only have 2in of topsoil are just a few areas near existing concrete where I could not raise the soil. Most areas are 6 in not including mulch, but I know that higher is better.

Based on peoples comments, I think my go-forward plan is to to add small amounts of a fast acting sulfate amendment to the higher pH topsoil before I add any plants. I'll monitor pH levels at the surface and add slow acting sulfur if I want to make other minor adjustments. But it seems that pH might not be my biggest worry- the soil should naturally drop to a more acidic level. I think raising the beds more and adding organic material might be the more important task.

I guess in the long run, the plants will tell me if they are unhappy. Is there any easy way to determine if a plant is unhealthy because of wrong pH or because its getting water logged roots? Too high pH or too much water will both cause yellowing, right?

Many people may try to tell you that you can look at a plant an tell what the problem is but while many will tell you that a yellow plant probably is deficient in
Ion, a micro nutrient, it is much more complicate than that and can be the result of a nutrient imbalance sometimes because of too much of one nutrient that interferes with a plants ability to utilize another. The best way to know if the soil is in a good healthy condition is with a good reliable soil test. Your plants will tell you if they are unhappy and the insect pests will help by eating them.

Un less you purchase a lab quality pH tester, very expensive, those pH testers from your local garden center are not very reliable. I have gotten the same pH readings with them from Vinegar and a baking soda solution. A soil test from TAMU costs $10.00 per sample and gives you a good idea of the nutrient levels, and pH, of yur soil. Some other soil test are these simple ones.

1) Soil test for organic
material. From that soil sample put enough of the rest to make a 4 inch level in
a clear 1 quart jar, with a tight fitting lid. Fill that jar with water and
replace the lid, tightly. Shake the jar vigorously and then let it stand for 24
hours. Your soil will settle out according to soil particle size and weight.
For example, a good loam will have about 1-3/4 inch (about 45%) of sand on the
bottom. about 1 inch (about 25%) of silt next, about 1 inch (25%) of clay above
that, and about 1/4 inch (about 5%) of organic matter on the top.

2) Drainage. Dig a hole
1 foot square and 1 foot deep and fill that with water. After that water drains
away refill the hole with more water and time how long it takes that to drain
away. Anything less than 2 hours and your soil drains’ too quickly and needs
more organic matter to slow that drainage down. Anything over 6 hours and the
soil drains too slowly and needs lots of organic matter to speed it up.

3) Tilth. Take a handful
of your slightly damp soil and squeeze it tightly. When the pressure is
released the soil should hold together in that clump, but when poked with a
finger that clump should fall apart.

4) Smell. What does your
soil smell like? A pleasant, rich earthy odor? Putrid, offensive, repugnant
odor? The more organic matter in your soil the more active the soil bacteria
will be and the nicer your soil will smell, to a point. Too much organic matter
can be bad as well.

5) Life. How many
earthworms per shovel full were there? 5 or more indicates a pretty healthy soil. Fewer than 5,
according to the Natural Resources Conservation Service, indicates a soil that
is not healthy.

kimmq is kimmsr

That's why I asked about a pH tester. Cheap ones are notoriously unreliable. I'm not an expert, but glass electrode ones like yours have some standard of credibility. But that's correct that a TAMU soil test is inexpensive, and will tell you more than you need to know. You could do separate tests for the topsoil and gumbo, I suppose.

What is the pH of the water you are irrigating with? That could determine what you're going to end up with. Not sure where you get your tap water, but the Trinity River basin water is pretty alkaline, with pH of order 8.

kimmq, Thanks for the tips. I'll do those tests and see what I come up with.

Dan, I did try to take the pH of my tap water, and discovered something. My meter is not holding calibration for long at all. To a point where I suspect I need to get a new electrode, or at least clean my old one. I think it might have dried out for too long, either that or the fine clay particles have dirtied the sensor. Getting the TAMU soil tests is another easy check as well.

You should store a glass electrode in distilled water to keep the glass membrane hydrated.

Your local water supplier (unless you have a well or a small private system) should publish an annual report that includes the average pH of the water they're delivering.

But you also want to know the alkalinity, which is a measure of the total amount of carbonate and bicarbonate. If it's fairly high, the water has buffering power, which means it takes more acid to reach neutral or acidic pH than it would if you had distilled water at the same alkaline pH. The water utility will have all that info too.

Beaumont has a low amount of bicarbonates in its water, but Houston will probably be pretty high. Our water comes from an East Texas water supply while Houston depends on water from the Trinity river. Lake water tends to be lower in bicarbonates than well water. Your water supply should have a report of it though. It is on the City of Beaumont's website. Under 100 ppm of Bicarbonates is low, 125 medium and over 150 is high, at least for blueberries.

Thanks guys. My water supplier gives us an annual statement, but it only lists contaminants (lead, copper), not more basic things like pH and bicarbonates. I'll have to contact them to get that information.

Not sure why people are saying acidification is so difficult...