soil amendments

Asked June 19, 2017, 12:51 AM EDT

Our land prior to our house build was just grassland (rural community). Soil is very rocky/clay. The area that is now my edible garden space was essentially grasses/dandelions overturned by a backhoe during the building phase. It was never tilled. I had my soil tested and advised to raise the ph, add lime and a few other minerals. I spoke with local compost supply company who recommended their Planet Earth brand due to higher pH of 7.4. I laid it over the turned dirt and made "raised beds," aka mounds with the compost which I've done before for many years with great success and planted starts. Over the past several wks, plants have not grown and are mostly dying. Based on my assessment and research, I believe the plants are showing signs of alkalinity toxicity/too much lime. At this point, what can save my garden if anything? I'm considering: 1) digging out all starts, removing some of the compost and tilling the rest into the overturned dirt (tilling for this year only). 2) amending the soil again the other direction with a manure, or?...but that doesn't seem like it would be enough? Help? Thank you!

Clackamas County Oregon

15 Responses

Thanks for your question about your soil. Yes; it appears that the combination of your adding lime and the high pH of the "Planet Earth" has raised the pH too high for bedding plants. (As you have undoubtedly researched, depending on the plant, they need it between 6.0 and 7.0. Above that, and the nutrients are toxic.)

The 'solution' for most soil problems is to add organic material, which helps both with pH and soil texture. It is available bagged and by the truckload, depending on the size of your gardening space. The best would be earthworm castings; but they can be expensive. An excellent second choice is well composted steer or chicken manure.

Rather than pull out your plants, you can top dress them with compost; it will eventually work its way into the soil through the work of microbes. Whether that will happen in time for them to be productive is problematic. Here is a link to an OSU article about the benefits of compost in the soil, and methods for creating your own compost into the future. If purchasing compost, attending to the analyses on page 7 is helpful.

Hope you can salvage your garden. Good luck!

Thank you Kristena,

I will be getting steer manure today and top dressing for sure...and thank you for the quick reply as I'm off today and can provide first aid to my garden. I think I'm also a bit confused by the term "compost" as the blend that I purchased "Planet Earth" I thought was supposed to be "compost" but when you used that term it appears you are referring to animal by products (earthworm, steer/chicken). I thought what I was adding originally (that's the high pH) is actually compost that's good for the soil? Could you clarify what "compost" really means?

Compost actually has a LOW pH (it's acidic.) It can be too low (too acidic) and prohibit the uptake of calcium, for example, which causes blossom end rot in tomatoes, peppers and eggplant, among others. But if it's much higher than 7.0, when it's called 'alkaline,' the nutrients actually can become toxic to the plants.

Here's a short explanation: "Why is compost pH worth measuring? Primarily because you can use it to follow the process of decomposition. Compost microorganisms operate best under neutral to acidic conditions, with pH's in the range of 5.5 to 8. During the initial stages of decomposition, organic acids are formed. The acidic conditions are favorable for growth of fungi and breakdown of lignin and cellulose. As composting proceeds, the organic acids become neutralized, and mature compost generally has a pH between 6 and 8."

As you requested, the definition of "compost" is just decayed plant material used as a fertilizer. This is consistent with animal manure (including worm castings), since animals eat plant material, and it decays back to nutrients that formed the plants in the first place. One reason we recommend against using manure from omnivores (that eat both plants and other animals) is that the manure can carry bacteria that cause illness, unless either heated or left to 'rot' for a sufficient period of time. Poultry manure is too rich in nitrogen (because the chicken's urine and feces are mixed, and urine is urea.) However, after being left for 6 months or so, microbes have sufficiently broken down the plant material, and it acts as the article describes.
I doubt that just the addition of the "Planet Earth" caused the soil to become too much closer to alkaline. I think it was a combination of that plus the lime you added. So well-aged compost will return the pH to or below 7.0, where your garden plants can tolerate it. This article may be a bit wonky for you, but it describes how the pH of the compost can be measured. (I doubt that any commercial sellers go to this much trouble!)

Hope this is more helpful!


Would your answer change at all if I clarified that the only thing that was added was the Planet Earth Compost and no extra lime? Sorry for the confusion, I originally only meant that lime was needed, so we assumed we'd get enough from the Planet Earth mix, no extra was added on top of that. Since that was all that was added, am I missing something else that could be killing the plants? I've been gardening forever, I've never, ever had anything like this happen to my plants before. This is the first time I've used this compost mix and was specifically told the pH is 7.4.

It's funny; I just called 4 companies that supply compost (although not Planet Earth), and no one of them could tell me what the pH of their (in some cases multiple types of) post was. The advertising of Planet Earth compost says nothing about its pH, so that part of it is a mystery!

So, let's take pH off the table for a bit. Could you please send pictures of the plants that aren't doing so well, pictures of any plants that are thriving, as well as a photo of the entire garden? Other than the Planet Earth, have you added any fertilizer, chemicals or applied any pesticides within 30 feet of the raised beds? (You said an addition of some 'minerals' was recommended. What were they? Did you add them?) Perhaps I can detect a pattern once I can see exactly which plants are having difficulty.

Thanks for any additional information!

Planet earth is from Dean Innovations, nothing else was added, and we are herbicide/pesticide free, aka organic.
The strawberries planted about a week later are doing well. Tomatoes and squash look the worst. Despite the dry appearance, soil is moist-shouldn't be a watering issue.

What I can see is an enormous amount of non-composted bark and wood, that is not well enough broken down to provide any nutrients to the plants. It may be acting as a mulch, by curtailing weed growth and holding in moisture, but good compost feels like coffee grounds and smells like a clean forest. I think the particles are just too large for an effective nutrient exchange and the plants are starving to death. And the large pieces of wood aren't able to retain enough water for the roots to take up water and food.

The plants on the right in the right photo (tomatoes or peppers?) are chlorotic (lacking nitrogen), and won't have enough chlorophyll to produce any fruit. The plant nearest the camera in the left photo appears dehydrated, but the leaf curl can also be a symptom of insects or fungus. However, either of those can appear when a plant is in distress from nutritional and/or hydration issues.

I'm back to my first recommendation. Take out as much of this stuff as possible; bring in some well aged, small particle, organic compost, side dress, and keep watered. You may lose all or a significant part of this planting, but your ground will be ready for the next season.

Good luck!

I literally ordered 65 yards of this planet earth which is advertised as organic compost. Here's a link:
I just called them any they're saying the pH is now 7.6. If I'm understanding you correctly, what I ordered is not what's advertised?

It appears to be what is advertised: a top dressing for the 2 to 3" above the soil. I just don't know if they intend for it to be used as the primary soil material. And the size of the fibrous material (woody) are certainly larger than "oatmeal to cornflake." Unlike fungal hyphae, plant roots simply can't take up water and nutrients from those chips/shreds.

If it really has a pH of 7.6, it's too alkaline and not within the range needed by your plants. That is perfectly consistent with iron chlorosis, but the plants would have to be tested to see if that is the cause of the yellowing.

Thanks for all your help, it's so nice to have this service. I will remove the bulk of the compost to just a few inches and mix in some steer manure. Then work that in just with a shovel with the existing soil...hopefully it will save this year's plants. Cheers!

Great plan! Just keep the compost that you move. Suggest you pile it up somewhere on the ground (so microbes, including fungi, can access it and 'do their work' over 6-12 months). By then, it should be adequately 'cured' that you can mix it in next spring, and have more healthy plants than you know what to do with!

So, I did that exact plan, and for the heck of it bought a number of new starts and planted them in my new and improved beds near the existing old plants to compare. For the record, the old plants look exactly the same still now after re-planting in the "improved beds". Some are producing a fruit, literally like one tomato or one tomatillo, but the stalks/leaves and noted even the roots look stunted, dry, yellow or purplish, like nothing is growing. The new plants look just as bad and appear to be having the same problem-no growth and yellowing. I am watering daily but with a sprinkler vs soaker hose (historically used soaker hoses but I cannot get the soaker hoses to work right as my garden is on an incline). I really don't think I'm over or under-watering but maybe I am? You mentioned that some of my plants looked dry? The soil remains moist but neither dry or drenched at the root level, in some cases though too wet due to the packed/clay original soil. I don't know if this matters, but I do notice a lot of mushrooms growing in this compost...not sure if that means anything. Is it just that this compost is that hot and needs a year to cure so that's why even new plants are dying in 2-3" top layer along with steer manure and the original soil? I've always had a very successful and flourishing garden...this is just so weird and sad to see these once beautiful starts look so pathetic.

I'm wondering if there has been some herbicide that was applied on or near your garden. Many broad spectrum herbicides (or pre-emergence ones like Preen) have a long half life. Has there been any spraying that could have drifted? You said was grassland. Was it treated with anything? You didn't have any testing for toxins or heavy metals (contaminants) that you mentioned initially. The growth of mushrooms is an indication of fungi in the soil, but they survive by 'eating' fibrous matter that is to be expected (and desirable) in compost. What is more troublesome, however, is the possibility of fungi that are pathogenic (harmful) to living plants. The scientfic approach would be to take up some soil to fill 2 or 3 containers (all with drainage.) Then fill 2 to 3 like containers with commercial potting soil. Buy as many plants--say, 6 identical tomatoes. Water and fertilize exactly the same among all, and see if it's 'them' or 'you.'

re: herbicide. We have lived adjacent to the property for 2yrs and no spray in that time. It was grassland, aka, dandelions and grasses for decades. How long of a half life are we talking? To note: the people that owned the property when we bought it are still living on their half of the property which is adjacent, and have a thriving flower garden. Everyone around us who has planted vegetables are getting good results and have for years (we're rural farmland). I do see what seems like a good number of earthworms at the level of the original soil.
re: testing for toxins/heavy metals. No, I will consider if I should, didn't know it was an option.
re: scientific approach. I have herbs growing separately in a large raised bed we made but in there we added organic potting soil instead. The herbs are growing fine.

Is there such a thing as paying for a consultant to come out and look at it? Hopefully this is our forever home, I'd like to ensure a happy, healthy garden for years to come. Thank you.

I'm trying to determine whether there might be any Master Gardeners who have businesses in garden/soil whom you could hire. (Master Gardener volunteers aren't allowed to do that as a part of the volunteer role.) I will get back to you within 48 hours, after I consult our program administrator here in Clackamas County.