Reusing Soil

This may seem like a silly question, but can I reuse soil from one year to the next? I'm a newbie LOL- but I do container gardening (I'm in an apartment) and I still have all the pots that my early annuals were potted in at the beginning of the summer. Although they've been gone for a long time, like the Bachelor Buttons, can the soil be kept for next spring or should I just get rid of it? Thanks all!
Samantha

I had a large container last year and after the plantings were gone, I mixed in a good portion of compost material and added some worms. We had long mild fall and late spring. Come planting season, that container performed best. I wonder if it was just luck of matching the plants or composting in the soil is faster.

A slightly different perspective and why I hold it:
If the decision to reuse container soils is an economic one, who can disagree with the decision? If you aren't concerned about expense and are willing to go to some minimal extra effort to build a good soil, that is what I would elect to do.

Here's why: Container gardeners need to direct primary focus to insuring that the soil they are using will remain able to provide adequate air to roots for the expected life of the planting. Along with the ability of the soil to hold ample air, comes good gas exchange and drainage for rootage. All the other major cultural variables affecting growth are easily manipulated. Water, nutrients, sunlight, and to some degree, temperature can all be controlled easily. Aeration cannot and its consideration is as important as water and light to plant vitality.

The breakdown or collapse of soil structure occurs at an exponential rate. If we imagine the usable life of a peat based container soil from a bag, it deteriorates from a reasonably good soil when fresh to unusable after 2 years. It's not unreasonable to expect the soil to lose at least 20-25% of its air holding ability by the end of the first growing season. In the first half of the second growing season, it will lose about another 25% of its air holding ability and in the second half of the second year, near total collapse is likely as the remaining 50% is lost. Though this is an example of an imaginary soil, it is very close to what actually occurs. Another way of saying it is: Even though a soil might be performing acceptably at the end of the first growing season, you should expect a rapidly accelerating collapse in the subsequent year.

So, if you use a soil for 1 year and mix it 50/50 with a fresh, similar soil, 50% of the soil will have totally collapsed by the end of the growing season, and the other 50% will have lost about 25% of its ability to hold air. If a soil is not holding enough air, it's holding too much water. Water and air retention vary inversely in soils and when one increases, the other decreases. When soils hold too much water, you have to hope that the plant will use enough water or that enough water evaporates to prevent root rot issues and even minor cases of over-potting can mean terminal misfortune.

Additional considerations are possible carry-over of fungal spores, the possibility/probability of insects in various stages (eggs, larvae, etc) and build-up of carbonate precipitates from your watering water. A slow soil will also have accumulated fertilizer salts and possibly insecticides that you may have applied and forgotten about last season.

I suggest that container soils be turned into the compost pile or garden and fresh soil used in its place unless monetary considerations prohibit.

Al

So Al, what do you suggest for plants that live in the containers all the time? Would you remove them every so often (say, once a year) and repot them in fresh soil?

Thanks,
Dee

Yes. It's not so important to replace soil per se, but it is important, if you wish plants to grow normally, that A) roots have room to grow and there is a reasonable volume of absorbing (fine) roots as opposed to transporting (larger) roots, and B) soil collapse hasn't made an issue of a lack of air to the roots and provided an environment favorable to rot fungi.

I build >30 containers of "pretty stuff" for the garden & decks each year. These soils are all pine bark based & they perform very well. I've even used them on occasion for more than one season for various reasons, but generally, these soils get turned into a compost pile or into the garden. I also maintain well over 100 other woody plantings. The soils I use for these plantings contain a high % of inorganic particles and are designed to retain their structure for extended periods (two years or more). Structure and the intended life of the planting are key in any discussion of container soils and in deciding on which components to use (or amend with).

Perennial plantings (trees and shrubs are perennials too) will all eventually benefit from a regular root-pruning or division, but that is a subject for another day.

What container soils are made from is very unimportant, as long as they are not phytotoxic (poison to plants) and they hold air and water in the appropriate %s. I often speak out against the use of sand, compost, and topsoil in containers because of the detrimental effect these components have on drainage/ aeration. Earth worms are one of the last things I would intentionally introduce into a container. They simply accelerate soil collapse and provide nothing special that couldn't be provided with the addition of your choice of either organic or chemical macro or micro-nutrient supplements.

Al

I always empty out my container plants in my "hell strip" beds where I am trying to build up soil in February or early March. I use those beds for trialing out xeric plants before using them elsewhere on the property, so what matters more is the organic content rather than any remaining fertility in the soil. Also it gets baked like a brick in a kiln, and any critter than can survive that should get a medal of honor.

Thanks, Al, for taking the time to reply. Lots to think on here! Good thread!

Dee

Amen Al, Ditto Al, Ya You Betcha Al. One way I continue to enhance my plants in the house as far as nurtition etc is to use compost tea as the water source and transplant into a 1 to 2 " bigger pot every 2 years. Any loose left over potting soil goes into my compost.

Very interesting thread. What about pots of soil where I've attempted to root cuttings and for some reason a few of them did't root, do I have to throw out the soil or can it be reused?

tapla, Why are worms beneficial to a garden bed but not a potted plant?

Worms improve the structure of in situ soils (5-10% organic & the rest mineral) by burrowing & aerating the soil while organic materials passing through their guts are broken down into elements the plants can assimilate. In container soils, that are usually already extremely high in organic content, we should have already considered aeration and be doing everything we can to insure it remains at adequate levels for the intended life of the planting. Add a few earthworms to the equation, and soil structure is quickly destroyed. The tiny particulates they create settle into small macro-pores or even micro-pores, compromising the soils ability to hold air and slowing drainage as it increases the water-holding capacity of container soils. Worms add so little in the way of nutrients that cannot be had by the addition of organic or inorganic supplements, that their presence is to be considered a soil malady rather than a boon.

The physics of container growing are entirely different from what we see in gardens. For one thing, the subsoil in gardens acts as an endless wick (hopefully! - clay soils and bedrock can be a problem as well as poorly drained soils, but by & large, the earth really is a huge wick), pulling water downward with the help of gravity, away from tiny air pockets surrounding plant roots, where in containers we have a "perched water table" to contend with and the necessity of being very concerned about how we manage it.

Al

THOSE ARE FIGHTING WORDS Al! Hee Hee My worms are the soil inspectors and quietly pass through soil highly airated and are like boyscouts leaving nothing behind but a deeply trenched commode. Yes they leave behind very little, but that very little is highly sought after by the plant striving to assimilate the materials from the inorganic debris that is frequently dumped into the soil that is too ionic to be used after formation of salts that occur immediatly after contact with the soil acids. worms are the soil vacuums that prepare the next use of the earth. I agree 100% with the rest of your knolwedge and commend you on your perspective but let my bugs and worms exist in the pots to regenerate the needed structure and chemicals for procreation and photosynthesis. I think that house and potted plants are greatly benefited with the waste and contact with the earth that the migrating annilid does in the summer to my house plants setting on the soil in the summer.

tapla, Thanks for your info, it makes sense. I'm just beginning to use organic methods so I need to undrstand what makes soil healthy and what is distructive.

It's hard to change old habits - like reusing soil in pots - but I've begun dumping it in low spots in the lawn so I don't feel that I'm wasting it. About puting it in the compost pile--If it has any disease or virus spores won't they contaminate the whole pile or will the heat of a hot compost pile kill them? What about a cold compost pile?

Oh Sofer - no need to be at odds - plenty of room for dissenting opinion. ;o)

All readers: I often find that people that are very knowledgeable about in situ soils are most likely to have a tendency to want to carry what works in the garden into the potting shed & apply it to container culture. However, when all my ramblings are distilled, I'll stand by the simplified idea that container gardeners need to maintain aeration in their soils at all costs. I'll still contend that adding earthworms to container soils shortens the serviceability of organic soil particulates (these particulates must supply the macro-pores container soils need to insure good root vitality, and diminishing their size reduces o/a air volume) while accelerating soil collapse.

Speaking to the issue of dependence on worm galleries to provide aeration, I'm left to ask two questions:

A) Worm galleries (burrows) are delicate structures and would be compromised at each watering as they would be easily collapsed and/or clogged by the fine particulates left behind by the residents. Frequent watering means that these burrows would need to be renewed to bring aeration back to soil. Why create or allow a condition in our containers that is so likely to require remedial action?

B) In view of the increasing reduction of particulate size caused by earthworms, and since containers are generally very hostile environments for things burrowing, what to do when temperature, over-watering, or a chemical kills the entire population of worms in the soil? What to do then when left with a soil that has been depending on worm galleries for aeration yet has had its particulate size severely reduced and is holding too much water? I contend that the very best scenario in even very short term plantings is an unnecessary risk.

We easily provide the major elements in container culture by adding fertilizers - organic or chemical, as is your wont. Earthworms are of some advantage in getting the minor elements into usable form for plants, but there is nothing magical about what they leave behind. We can provide the minors with the simple addition of any one of several organic potions or easier yet with the addition of things like Micromax or STEM and or other, recently arrived fertilizers that contain the minors.

Thats all I have for now. Good discussion BTW :o)

Al

Okay,
I think I get the drift. But what do you mean by minors? Are those chemical or organic or what? I have never heard of Micromax and STEM. What do they offer us?
Betty

Hi Betty. Hope this is still appropriately on topic so as to not constitute a hi-jacking of Phlower's thread. The majors are N, P, K, magnesium, calcium, and sulfur. The minors are iron, boron, zinc, copper, manganese, molybdenum, chlorine, cobalt, and nickle - I think that's all of them. Elements are elements and plants don't care how they're made available (chemical or organic), only that they are. Micromax and stem are granular or powdered forms of micro-nutrients, the difference between the two being that Micromax is insoluble in water and very slow acting while STEM is soluble and immediately available for assimilation.

Al

Thanks for the info. I, too, have often wondered what the best way is to handle soil for potted plants. The info you have posted here will be very helpful. Thanks. Betty

I agree with you Al on the plant does not care what form they come in but the soil has to live with the left overs of the inorganic carrier so humbly I think that from a "republican save the earth perspective" those salts and inorganic byproducts are less valuable. They require leaching to eliminate and in so reduces soil value. Albeit only a short time in a wet climate but here in the alkaline prarie lands is significant. I agree adding worms is not a significant benefit but utilizing the chemistry of the compost pile is. There fore the micros, Macros, and soil bacteria more than assist the potted plant in the form of compost tea. I suspect we are in agreement on all but source.

For others who might be following this exciting (lolol Well, it is to me.) ;o) conversation about soils, I'll make the note that it seems we have something of an agreement now on the earthworm issue, and have shifted our focus from earthworms to the "chemistry of the compost pile".

My take on the "salts and inorganic by-products" is that leaching is imperative in any container soil. That is why I insist that my soils are open and porous enough to water freely, and practically at will. There is probably no greater danger in a build-up of fertilizer salts than there is in a build-up of dissolved carbonate solids that will result under certain conditions from irrigating with alkaline prairie tap water - any, other than de-ionized, water for that matter. Both conditions carry risk of reverse osmosis (plasmolysis, aka fertilizer burn) in slow, poorly aerated soils or in plantings that are "over-potted" & by necessity, irrigated in "sips".

Soferdig - Of course, we are in agreement that plants need all the nutrients, major and minor to perform as near their potential genetic vigor as container culture allows. I haven't been around this forum long, or followed its posters closely, but it seems that you're a proponent of organic methods in both the garden and containers. I have no reservations about "source" when it comes to plant nutrients. I'm not bound by a particular ideology in my cultural (growing) habits, but even if I was a hard-core "organics only" grower, I'd spend little time worrying about the compost chemistry of my container soils. Abundant populations of micro-flora/fauna in soils are more likely to accelerate soil collapse and the accompanying/subsequent anaerobic conditions I believe we should consider our first priority to prevent. Add the fact that soil organism populations are going to be boom/bust due to practices like irrigation, fertilization, and particularly soil temperatures in containers, the inherent lack of many (both major and minor) nutrients in container soils, and you create a dependency on a generally unreliable delivery system. Instead, if I was practicing under a self-imposed "all organic" rule, I would institute a regimen of regular nutrient supplementation with a reliable organic delivery system (an organic fertilizer and micro-nutrient source), which could of course include compost tea.

Though I do use chemical fertilizers, which I find fast acting, reliable, and efficient, I always allow that there are others that entertain alternate values when it comes to their growing efforts. I hope that my observations remained respectful of your ideas about container culture, and that I might have even offered some food for thought - for you and any others listening in.

Take care.

Al



This message was edited Oct 15, 2006 8:26 PM

Yes Al I am a avid natural nitrogen man. As far as organic only I always defer to the most efficient and practical response to soil needs. The only difference is 'here' if inorganics are used in high calcite water we see the deposition on the soil and performance of the plant in the limited soil used in pots. You guys in the mighty great lakes have no such problems and inorganic 'left overs' just go out the St Lawrence. Here they stay. I appreciate the lessons I am learning from you and believe me I am not the source of any knowledge but what has worked for me. I used miracle grow for years in seattle and had no trouble but here in Lime city we cannot without biannual soakings in spring and fall rain.

Just musing now, but I think that you "could" return to MG if you use a well aerated mix that required frequent applications of water & fertilizer, depending on the irrigation water to carry residuals away with it as you flush the soil at each watering, but I respect your wont to protect the environment. Watering practice has a big impact on carbonate/fertilizer salts retention.

If I could describe a "perfect" method of irrigating this type of soil, it would be this: A) Irrigate soil just enough so soil retains all the water you apply, and is nearly saturated, but none runs from the drain hole(s). B) A few minutes later (10, perhaps) return and water again, but this time irrigate so that about 10 - 15% of the total volume of water applied in both applications runs out the container drain. This method/volume is enough to dissolve accumulated salts and carry them out of the container while having minimal diminishing effect on nutrient levels.

Of course you can apply organic fertilizers like fish emulsion in formulations appropriate to plant material, but they will be slower acting & their availability for assimilation is less reliable as it is dependent on the boom/bust cycle of soil organism activity for reduction to usable forms.

Al

Since I have gone to compost tea once monthly in Spring to summer waterings my plants have thrived. Where as before they did well and hung in there. I attribute it to soil bacterias, molds, trace elements, which all come from the breakdown of other plant material. I will probably never go back to MG except in the spring outside garden.

Wheeewww! Thanks for a very interesting thread indeed! Enjoy reading the reasonings and science supporting what we all really want.. excellent container soils for excellent container gardening. ;0)

re: "Since I have gone to compost tea once monthly in Spring to summer waterings my plants have thrived."

Yeah, but it tastes like old socks.

Hee Hee Hee Heee That's funny greenjay! I thought it tasted like summer bass. Kind of muddy with a hint of tannins, the bouquet is fleshy, but full of exuberance. LOL

No wonder you guys' humour is so tainted!! ;0)

"Abundant populations of micro-flora/fauna in soils are more likely to accelerate soil collapse and the accompanying/subsequent anaerobic conditions"

Do you have any references to support that type of statement?

Its been my understand that microfungal strands in soil increase aeration in the soil pores and create soil structure... Micro-Fungal strands in the soil create a web of macropores that I have read significantly increase soil aeration, water infiltration and water holding capacity. Which is why compost (and teas) are thought to be beneficial to soil, whether in a container or not.

I think some of that information was gleamed in one of the many volumes of "The Container Tree Nursery Manual" put out by the US Forest Service?

But I have also done alot of reading about the soil food web and I believe this web can be somewhat mimiced in a container situation, to the benefit of the plants.

Without getting too deeply into it, can you allow that increased activity of soil biota must accelerate the reduction of soil particulate size? Does it not follow that diminished size reduces not only air porosity, but total porosity as well? Of course it does. Now, even if we allow that fungal associations can at times "increase soil aeration, water infiltration and water holding capacity", it doesn't mean they will, or that we should depend on them to do so. To depend on living organisms as an important part of container soil structure is to take a risk. If the living portion of the soil you depend upon succumbs to any one of a number of unfavorable cultural conditions it is likely to be exposed to in containers, soil can collapse (remember, the decrease in particulate size predisposes the soil to collapse). If this occurs, it is then even possible that the favorable conditions once found in the container that allowed the organisms to occur might have been altered by the organisms themselves, making their return to the soil something less than assured.

It's almost (but not quite - I'm not complaining) not fair that you didn't include the sentence in my post subsequent to the one you quoted. "Abundant populations of micro-flora/fauna in soils are more likely to accelerate soil collapse and the accompanying/subsequent anaerobic conditions I believe we should consider our first priority to prevent. This one: Add the fact that soil organism populations are going to be boom/bust due to practices like irrigation, fertilization, and particularly soil temperatures in containers ..." Knowledgeable readers might extrapolate that the "bust" portion of the cycle cannot be a good thing when you are biota-dependent for soil structure. IOW, it's not always a perfect world & we need to be prepared for that possibility.

I'll return to my original premise that a container gardener's first priority should be to insure that soils retain their structure, particularly as it relates to drainage and air-porosity, for the life of the planting. If there is disagreement in the face of my offerings, I'll levy the onus of refuting my assertion(s) on challengers. I'd also note that the contended point is rather parenthetical to the conversation and not pivotal to the thread.

Al

Actually I cannot agree with the statement: " increased activity of soil biota must accelerate the reduction of soil particulate size"

Everything I have read indicates that the fungal portion of the soil food web builds soil structure it does not break it down into smaller particle sizes.

One example: "Fungal hyphae physically bind soil particles together, creating stable aggregates that help increase water infiltration and soil water holding capacity." taken from NRCS Soil Biology primer.

Now that is not to say that I think that all the biology of insitu soil can be replicated in a container. But I think to ignore the biological component of soil or to even go as far as presume the the biological component of soil is somehow harmful in a container,,, seems to me to be a huge disservice to the plants that grow in that medium. Just my opinion...

And in addition to the soil structure that micro fungals provide, there is a huge relationship between fungals in soil and the nutrient uptake of plants. Roots are much more efficient at absorbing nutrition in fungal laden soils than they are in the absence of such.


And to get back to the thread at hand - I typically toss my used pot soil into the compost pile - and eventually it does get recycled back into a new pot when I mix compost into my container soils.

And any diseases that might be in the potting soil will be consumed by the microherd in the compost pile, creating a microherd capable of consuming that disease should it re-appear again. In essence, potentially providing some immunity to that disease in the future.



This message was edited Oct 19, 2006 4:59 PM

That you don't agree is a good thing. It allows the readers to weigh arguments & decide on the validity of each, but just as pork or beans passing through our guts is broken down into tiny particulates, so are cellulose, lignin, suberin - the hydro-carbon chains that make up our highly organic container soils broken down in the guts of soil biota. They (soil bugs) require nourishment like you and I and the source is the organic component of our soils. Yes, we differ here in that I think it an easily recognized concept.

I agree with much .... no, almost all of what you say as it applies to the garden. This: "Fungal hyphae physically bind soil particles together, creating stable aggregates that help increase water infiltration and soil water holding capacity." taken from NRCS Soil Biology primer. is obviously written in reference to garden soils, soils of high mineral content - >90%. This relationship is far less important in container soils. In fact, it is of little significance. I grow many plants (some photos circulate here at Dave's) in 100% inorganic container soils that are perfectly healthy. The soil provides the anchorage and air the plant needs & I supply the water and nutrients. I'll risk a little cheekiness here when I say that based on the plants proximity to their natural genetic vigor, they are largely unaware of any disservice having been done them and care not a whit about soil biota.

In any highly stable soil, there is little worry about what happens to soil structure when any living thing that might provide that structure dies - not so in one that depends on living things for basic cultural requirements.

Al

I think we agree on a lot of points, including disagreeing is a good thing. My greatest concern is that some of your posts say that using organic methods (like compost, worms, organic fertilizers) harms soil structure in container situations - and I that is where we differ.

The mico-organic components of soil are complex web that is a continual process of breaking down organic matter AND building soil structure.

I also have success with containers using compost, compost tea and organic fertilizers. I have beautiful, thick lush plants in many many pots every year --- year after year -- and I don't have to rely on synthetic products for my fertilizers. The fungal component of soil is a key factor for many plants particularly woody type plants, whose roots depend upon micro-fungal to absorb nutrients.

I have never disagreed with any of your posts about soil structure, drainage, porosity and the importance of such in container plants.

However, I do wish that you would learn more about how organic methods can build soil structure in containers rather than flat out saying that its harmful. You are very knowledgeable about many topics and I, along with many other readers, value the information that you provide. But when you are providing information that is wrong, then I feel I must offer a differing opinion; so readers can see that there are different ways to grow container plants - and using organics does NOT "accelerate soil collapse and the accompanying/subsequent anaerobic conditions" as you had presented earlier.

Joepye~ since you have had "lush "plants in your containers for several years, could you please share with us, who are learning,...1.what ingredients and proportions thereof do you use for your soil 2. what ingredients do you use for fertilizer and how often 3. what amendments are added in subsequent months to sustain lushness.

I'm not here to produce more heat than light, and have no interest in parsing words, but let's get a proper perspective and keep things in context. My statement was, precisely "... I'd spend little time worrying about the compost chemistry of my container soils. Abundant populations of micro-flora/fauna in soils are more likely to accelerate soil collapse and the accompanying/subsequent anaerobic conditions I believe we should consider our first priority to prevent." I'm not ignorant of symbiotic relationships between soil organisms and plant life, and I'm sure I have a better working knowledge of soils than here credited with, but that is of little matter to me.

Being a bonsai practitioner puts me up close and personal with the relationship between roots and soils as I fully repot and extensively root-prune more than 100 plants yearly. An example of why I will not depend on the presence of soil biota for the delivery of nutrients and for the cultural requirements provided by soil structure can be had by a comparison of the extent of mycorrhizal colonization when performing spring and summer repots on plants that benefit greatly from the symbiosis provided by this fungus. When cultural conditions are conducive in spring, mycorrhizal colonization is evident and substantial. In summer repots it is usually not in evidence at all. Other soil organisms follow a similar boom/bust cycle with widely varying cultural conditions.

Now, you said in something of a blanket statement and in its own paragraph for emphasis The mico-organic components of soil are complex web that is a continual process of breaking down organic matter AND building soil structure. I agree with the first half of course, but we cannot depend on the second half as true. If it was true, it wouldn't matter much what the organic components of our soils were (we do not need an organic component btw). If we could depend on soil organisms to supply structure, we could grow in anything organic. Instead of pine bark, we might use chopped celery. We don't, of course, and the reason is that the boom cycle of soil organisms will break it down quickly & the soil structure that was technically so appealing to begin with would be destroyed.

Actually, we are not as far apart as it seems. I can agree fully with your "... there is a huge relationship between fungals in soil and the nutrient uptake of plants. Roots are much more efficient at absorbing nutrition in fungal laden soils than they are in the absence of such.", as it relates to garden soils. If I could eliminate one word - "huge" I would consider it true in containers as well. Our real difference lies in the fact that I contend that the micro-heard is unnecessary in container culture (evidenced by the ability to grow perfectly healthy plants in 100% mineral soils with virtually none of the soil activity discussed here) and it's presence "is more likely to accelerate soil collapse", and because of the extremely wide variance in their populations, we should not rely on their presence in container soils. (Was that a run-on sentence?) I'm getting to feel like I'm running redundant here anyway. I think we've presented our cases well & I'll watch intently as I offer you the last word.

Cheers. ;o)

Al

You guys need to accept your differences soil is flexable. Except maybe bonsai. Steve.

I am repsonding to garden6 at this time, as Al is still beating a dead horse. We have both made our points and can move on.

Anyway - I use cheap potting soil and mix it with about 1/3 compost. In very large containers, I will fill the bottom 1/3 container with packing peanuts and then cover those with a peice of filter fabric... to keep the soil out of the peanuts. I use Alfalfa pellets or coffee grounds for fertilizer. And I water using rain water as much as I can., I do use occaisinal tea made with rain water and alfalfa or rain water and compost.

I wanted to post of picture of several of my potted plants but my computer had its network card fried from lightening and I am posting from my husbands machine. I do have one picture on this machine, but its blurry and not a good pic.

The plants in this pot were seedlings less than 1" tall early this year. The soil in this pot is over two years old - I've reused it undisturbed for three seasons. (I probably woud not do that with a smaller pot). When I put the plants in, I found worms living in this pot. (I didn't put them there, sometimes, if you build it, they will come.) The bottom of this pot was filled with packing peanuts and straw - two years ago. And each spring when I add new plants, I top off with a bit of compost...

(And again sorry about the blurry pic, but its the only one I have on this machine.)


This message was edited Oct 21, 2006 8:20 AM

Joepye~ thanks for the information. Your container plants definitely validate your perspective. I really do appreciate you taking the time to share your recipe for success. After having several containers bite the dust early Sep. I'm open to trying your method ( I did use new bags of pro-mix ) Will update the results in Spring ;0)

I agree JoeP that any soil is brought back to life with the simple supplement of compost and some perlite. Though I usually use the piles of torn bags I get from the big box stores that are piled up in my back yard. I have so much that I use potting soil to top dress areas of lawn where soil is too thin to hold water during the hot summer months.