Questions from Readers: Help with my Forest Garden plan

Pawpaw (Asimina triloba) is a native to southeastern North America.

http://upload.wikimedia.org/wikipedia/commons/1/15/Asimina_triloba3.jpg

We have an existing "forest" area on our property that I was planning on turning into an Edible Forest Garden centered around guilds of Paw Paw trees. I am located in northern Alabama, in zone 7, and the area is full of pine, oak, privet, and honeysuckle. The soil is a rich clay full of organic matter (earthworms abound). But I just got the soil results back and the ph is a strongly acidic 5.3.

I am planning on doing most of my planting in the flat valley area, but I'm thinking that the rain water that runs off of the slopes on both sides of the valley will be acidic due to the pine needles, which has probably been the chief contributing factor to making the soil as acidic as it is now. So, while I could apply lime to the valley area to try to raise the pH there (making it more suitable for the Paw Paw trees), it sounds like keeping it more alkaline will be an "uphill battle." I'm also concerned of what it could do to the existing plant life (would I start killing my pine & oak trees, for instance?).

I pulled out my Edible Forest Gardens book by Jacke & Toensmeier, and it does look like I have a lot of acid-loving fruit-bearing alternatives I could plant. Prunus cerasifera (Myrobalan Plum), Prunus pumila (Eastern Dwarf Cherry), several species from the Ribes genus (currants, gooseberries, and jostaberries), several species from the Rubus genus (blackberries, cloudberries, black raspberries, etc.) and a wide variety of blueberries could be alternative fruit-bearing plants to the Paw Paws. There also does not seem to be a shortage of acid-loving greens (although I really want to plant Stinging Nettle and Good King Henry and they both like the pH to be at least 5.5. I guess I could apply lime to just a small area...

I guess my basic question is, would you work around the current pH of 5.3 and plant things that would work in the existing forest, or would you try to stick with the original plan of planting Paw Paw trees and amend the soil accordingly?

Your feedback would be greatly appreciated. Thank you.

Jennifer


Great question! There is a lot to this, so I am going to break it down a bit.

We have an existing "forest" area on our property that I was planning on turning into an Edible Forest Garden centered around guilds of Paw Paw trees. I am located in northern Alabama, in zone 7, and the area is full of pine, oak, privet, and honeysuckle. The soil is a rich clay full of organic matter (earthworms abound).
Fantastic! The more Forest Gardens we have, the better! I love the idea of Pawpaw (or Paw Paw or Paw-Paw) guilds, but don't limit yourself. There are so many great fruit and nut trees that will grow in your area. Just something to keep in mind. It sounds like you have a variety of trees and shrubs in the area that are tolerant of a wide range of soil pH. It also sounds like you have a very good soil with which to work. This is also very good news for you.


But I just got the soil results back and the ph is a strongly acidic 5.3.
I am very curious how this was tested. You didn't explain how many tests were done or how they were done, and this really matters. We often only test one spot, because this is cheaper. However, what if that one spot was a highly acidic location and the rest was not? What if a dog just urinated there? It is very tough to make a pH determination for a whole area with just a single test. Ideally, we would test multiple spots throughout our planned Forest Garden.  It also matters how we do the testing. We are often told to get a small soil sample from the top few inches of soil or dig a shallow hole, fill it with water, and test the mud. Well, all we are doing is testing that one layer of soil.

Basic Soil Horizon Layers

http://upload.wikimedia.org/wikipedia/en/5/51/SOIL_PROFILE.png

There are multiple soil layers in every area. Most locations have standard layers of soil abbreviated as O-A-B-C-R (O=organic layer, A=surface soil, B=subsoil, C=parent rock, R=bedrock). These layers are also called Soil Horizons. Some locations have fewer layers, but most locations have more. These Soil Horizon layers can divided even further:

http://hwwff.cce.cornell.edu/content/unit2/images/SoilHorizons.jpg

So, when we are testing soil pH, we need to consider which layer are we testing. Also, very few plants will grow in just the O-layer (which we usually test). Trees and shrubs will put down roots through many of the layers, and some trees will even burrow into the bedrock.

Finally, the pH of each layer is different. Sometimes, they are not drastically different, but oftentimes they are. I tried really hard to find some good references for this, but I was unable to do so quickly as I was writing this response. However, there has been some good research that shows that creating the "ideal soil pH" may not be all that important for perennial plants... IF the soil is a healthy, undisturbed soil. From the description given in this question, it sounds as if the soil is very healthy, and not hard-packed, recently tilled farm fields. Plants that desire specific soil pH, if planted in healthy soil, will seek the layer that meets its demands. So, for instance, if a plant prefers an acidic soil, then it will put out more roots in an acidic Soil Horizon layer.


I am planning on doing most of my planting in the flat valley area, but I'm thinking that the rain water that runs off of the slopes on both sides of the valley will be acidic due to the pine needles, which has probably been the chief contributing factor to making the soil as acidic as it is now. So, while I could apply lime to the valley area to try to raise the pH there (making it more suitable for the Paw Paw trees), it sounds like keeping it more alkaline will be an "uphill battle." I'm also concerned of what it could do to the existing plant life (would I start killing my pine & oak trees, for instance?).
I think you are looking at this with two sets of glasses on, and you are trying to decide which one gives you a clearer picture. The modern agriculture way of handling this issue is to decide what you want to do before you know your land. Then you evaluate the land and make it do what you desire. This requires a lot of initial work and a perpetual fight to prevent the land going back to what it wants to be. The fact you are asking these questions, means you are trying to avoid this path. Good for you!

The Permaculture way is to get to know your land and determine what would be best suited to it while still providing for your needs. This requires significantly less work initially, less money and investment, and significantly less maintenance. But it does require a lot more planning. This is working with nature! Don't get me wrong, there is a place for "working" the land a bit. But you have to balance this with how much work and environmental change (locally, I mean) you are willing to push.

In a sense, it may seem I am talking out of both sides of my mouth: pH doesn't matter... evaluate your land and pick species that suit it. Well, with pH specifically, unless we are dealing with a very sick piece of land that requires regeneration and rehabilitation, then I am really not too worried about pH.

When it comes to temperatures, sun exposure, wind exposure, etc., these factors are a bit more inflexible. But as I explained above, pH is a bit more complex, less predictable, and therefore less worrisome for me. I know I will plant some shrubs or trees that will not find a good niche on my land. I will try to help it get established, but after that, it is mostly on its own. I will help maintain it, but I do not want to spend a lot of time on it. If I did, I would spend more and more time on things that give less and less, or I will spend more money and time to "fix" a problem that would not be an issue for another plant.

So, here is what expect to happen. When setting up a Forest Garden, do your best to select species and varieties as ideally suited to your land as possible. Pick a few plants that fall outside of that range... within reason. Don't grow banana trees from the tropics in a windy tundra field. But we can  try to grow a plant that is best suited one or two USDA Heat Zones north or south in our forest. We can try to grow a few plants that have more or less moisture requirements that we currently have, because this can change and because plants can adapt. We can certainly plant a tree that prefers a more neutral pH in a soil that appears to be a little more acidic.

Expect to lose some of your plants. Some plants will not survive. This is part of gardening and part of forest life in general. I would prefer that this did not happen, but not every plant is going to be ideally suited to your land. You will get some surprises though. That tree that really prefers a bit more heat, may do very well, and that tree species that is growing great on your neighbor's land gets sick and dies within the first year. This is okay. This is part of Forest Gardening. When a plant dies or does not thrive, then remove it and try another variety or another species. This is also mimicking the natural succession in a forest.


I pulled out my Edible Forest Gardens book by Jacke & Toensmeier, and it does look like I have a lot of acid-loving fruit-bearing alternatives I could plant. Prunus cerasifera (Myrobalan Plum), Prunus pumila (Eastern Dwarf Cherry), several species from the Ribes genus (currants, gooseberries, and jostaberries), several species from the Rubus genus (blackberries, cloudberries, black raspberries, etc.) and a wide variety of blueberries could be alternative fruit-bearing plants to the Paw Paws. There also does not seem to be a shortage of acid-loving greens (although I really want to plant Stinging Nettle and Good King Henry and they both like the pH to be at least 5.5. I guess I could apply lime to just a small area...
These are all great species! I would say to try them all! I would avoid liming or adding specific soil amendments if you can, especially when you are talking less than 1 pH point. However, sometimes when you are dealing with very unhealthy soil, amendments will speed the healing process. As I wrote above, plant a variety of plants from a variety of sorces, and they will self-select. The ones that can tolerate a little variation in their requirements will thrive, and the ones that cannot probably do not belong in your forest.


I guess my basic question is, would you work around the current pH of 5.3 and plant things that would work in the existing forest, or would you try to stick with the original plan of planting Paw Paw trees and amend the soil accordingly?
One of the reasons I loved this question was that it showed me I was wrong! I really mean that. I love to learn new things, and new things really stick when I am corrected. I absolutely love the book(s) Edible Forest Gardens. I use it as a reference frequently. I realized I used it as a reference when I put together my article on Pawpaws. This was my mistake. I typically try to verify specific facts like pH requirement with at least three sources. I think since this was one of my early articles, and I was not yet in the habit of doing this. So I passed on this reference's mistake. (You are going to love this!)

Pawpaws prefer acidic soil! Today, I found just over a dozen references, and the most liberal state that Pawpaws prefer soil with a pH in the 4.7-7.2 range. I think conservatively we can say that most Pawpaws will do very well in soil with a pH of 5.1-7.0. I actually just updated my original article because of this.

After thinking about this, it only makes sense. Pawpaws are native to your area in the first place. They originate in the southeastern United States. Most of this area has native soils in the acidic to neutral pH range, so it would seem odd that this native tree would fall so outside that range.

Pawpaws will likely do very well for you in your Forest Garden.

So, the bottom line...

• Try to work with nature instead of fight against it.
• Don't worry too much about pH when you have healthy, undisturbed soil, and you are planting perennial shrubs and trees.
• Expect to lose plants as your forest matures and see this as nature taking some extra work away from you.
• Variety will give you the best chance for success. Nature doesn't create monoculture.
• Question all things. Verify with multiple sources. Don't be afraid to be wrong... you just might learn something new!

All the best!
John