Compost and Top Soil - Overkill?

LantanaLove(9 - Riverside, CA)July 23, 2014

Good afternoon!
I'm hoping that someone can advise me as to whether or not my quick-fix plan for one of my flower beds is a good idea or a waste of time/money...
Throughout this year, my husband and I have been planting flowers and vegetables in different parts of both the front and back yards. We've noticed that our flowers and vegetables in the back are nowhere near as healthy and vibrant as those in the front. In fact, they deteriorated so quickly that we've pulled 90% of the plants out.
The only thing we did differently from one yard to another was adding about an inch of potting soil on top of the clay in the flower beds in the front, and we planted directly into bare clay in the back. I believe the potting soil really help with water retention whereas the bare clay dried out way too fast.
I've attached a picture of one of the bare beds in the back where we plan to plant pumpkins. (This is basically a visual to show the difference between the compost and bare clay) We added 4 bags of EcoScraps organic compost as a new layer of topsoil. There is probably 1/2 inch of coverage and we really don't want to till it in. We were going to add about another 1/2 inch of potting soil on top of that and consider the bed prepared.
So tell me, do we even need the potting soil? Is it overkill or not nearly enough?

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tropical_thought(San Francisco)

You got to til it in or dig it in. Plants won't grow well otherwise, and the stuff you buy it bags may have something in it like too much added fertilizer.

    Bookmark   July 23, 2014 at 4:37PM
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LantanaLove(9 - Riverside, CA)

I've read that top-dressing with compost can be successful, it's just a matter of time for earthworms to help drag organic matter down into the soil and adding compost yearly after that...
If we do end up tilling it into the soil, how many inches of compost should we mix and how deep should we dig?

    Bookmark   July 23, 2014 at 4:50PM
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ken_adrian Adrian MI cold Z5

thats a lot of shade for full sun veg and a lot of the bigger flowered plants ... and lack of sun is not going to be fixed by soil amendments ...

try googling 'double digging' a garden bed ...

i dont know what potting media is going to add to mother earth ... if you wanted the peat.. then you could have just used peat ...

and if a plant puts roots down .. lets just guess.. 6 inches.. i dont think a half inch on top.. will have much or any impact ... in the short run ... so .. you are no where near over kill ... and frankly.. i dont think its enough ...

i dont understand.. comparing one garden to another ... too many variables to compare ...

good luck


Here is a link that might be useful: link

    Bookmark   July 23, 2014 at 4:59PM
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You are tossing terms around interchangeably that are confusing. Maybe you are confusing 'topsoil' with 'top dressing', a soil amendment applied to the top layer of garden soil. Topsoil is generally considered to be the top layer of natural soil before any clearing or construction. Compost is decomposed organic matter and potting soil is a medium intended ONLY for container gardening. Neither of these terms should be used interchangeably with "topsoil". Even bagged 'topsoil' is probably not the real thing.

Compost is typically used as a soil amendment to lighten and enrich existing soil, like your clay. 1/2-1 inch of compost is hardly sufficient to do much of anything!! And it should be incorporated into the existing soil before any planting. A uniform soil interface - the combining of two or more different textured, different structured soils - is extremely important for both good drainage and root development.

Compost or other organic matter is the primary amendment for improving soils of pretty much any kind. Add as much as you can afford (4-6 inches) work it in well and it will allow for good root establishment, moisture retention and nutrient exchange. You can purchase compost in bags from your local garden center or home improvement store, purchase it in bulk from a landscape supply or soil yard or make your own (takes awhile and never enough).

    Bookmark   July 23, 2014 at 5:00PM
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tropical_thought(San Francisco)

People who just top dress have first dug it in and then subsequently, put it on top. It can wash away for one thing if it's only on top with watering. Worms don't really move it around, they make tunnels, but we can't see them. At least I read they make tunnels, aren't movers. They could eat from the top and then poop in the lower part, but that still not like digging in, not really the same thing. What about a rototiller, or hiring someone to rototill the lots of compost in if you can't do it yourself? I have also heard compost and clay and not as good as compost and sand. You can also plant plants that like clay soil. You can find a list of them online. They don't have to be well drained. I forgot to mention a tip. If the soil is hard and you don't feel like digging it, if you put some good compost on the top of the soil and water it and wait 24 hours or so, the soil will begin to soften up. This is due to all of the good bacteria in the compost, which is sometimes referred to as the mircoherd by people on this forum. They soften the soil so you can dig in a little bit, then add more compost and wait and digging a bit deep each time until you dig at least 12 inches ideally or how ever deep the plant root for what you want to grow go. Clearly if you just want some pansies, you don't need to dig that 12 inches they suggest under the process of double digging.

This post was edited by tropical_thought on Wed, Jul 23, 14 at 23:21

    Bookmark   July 23, 2014 at 10:24PM
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nil13(z21 L.A., CA (Mt. Washington))

I sounds like there is some else going on other than one group being essentially mulched and the other group not. I would not expect one group to completely fail just because it wasn't mulched.

If you are planting annual flowers and vegetables, you will want to mix in a decent amount of organic matter into the soil if it doesn't have enough already (about 5% by weight). In a perennial bed I would just mulch and let nature mix it together, but bedding plants and vegetables can benefit from a more intensive approach.

If I were to guess what was going on with you plants, it would be that there was a soil interface problem between the clay and the potting medium that was substantially mitigated with mulch. The potting medium the plants come in will dry out much more quickly than the clay. The soil will look wet but the rootball will be bone dry resulting in dead plants. When you pulled the dead plants, had the roots penetrated out into the native soil or were they just in the container medium?

    Bookmark   July 24, 2014 at 12:50AM
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LantanaLove(9 - Riverside, CA)

The roots had penetrated the clay in all of the plants except the snapdragons and the azalea.
I was just hoping that the compost would add some nutrients and that the potting soil would help maintain moisture toward the top of the plants. My clay will eventually become moist further down but the surface dries very quickly. With seeds, this may be a recipe for disaster since I don't want to spray/mist them 10 times a day in this heat.
I was hoping for a quick solution for now and possibly do a full-on renovation at a later time.

    Bookmark   July 24, 2014 at 1:17AM
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It's better to plant in the cooler Spring for just the reasons you mention--heat and dryness.

If you really don't want to dig in your soil amendments, try lasagnia gardening to get a less expensive result.

Save bagfulls of fallen leaves, grass clipings, or whatever else you can get your hands on, and throw that over your clay, hopefully to a depth at least three inches.

Scatter your soil amendments on top of that. If you have any compost, use that first, then a bit of topsoil or even add some sand if you have any.

When you place your plants, make a hole in this top layer you have made and place each plant in its own hole. Fill these holes with the topsoil you have reserved for this purpose.

It's really surprising how quickly the top layer will turn into good topsoil, provided you have enough rain or water sufficiently.

The plantings will improve as the soil does.

    Bookmark   July 24, 2014 at 1:57AM
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What that soil needs is organic matter and potting soil is one source of organic matter because it will be peat moss, coir, or bark fines, or a combination of those. Compost is
OM as well.
"Topsoil" is a meaningless term and can be anything the packager/seller wants it to be. Maybe "topsoil" might be about 95 percent of the mineral portion of soil with maybe 5 percent organic matter. Concentrate your efforts on adding organic matter to the soil you have. Whether earthworms, and other members of the Soil Food Web, will work that organic matter into the soil will depend on how active that Soil Food Web is. Soils with very low levels of organic matter in the soil will not have a very active SFW so compost or other forms of organic matter will not see that moved into the soil very fast because there is nobody to do that.

    Bookmark   July 24, 2014 at 6:22AM
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toxcrusadr(Zone 6a - MO)

Definitely dig in as much compost as you can, and do it every year before planting, or in fall after annual plants are done. As the years go by the soil will improve and you won't need as much. Avoid digging clay when it's very wet. Don't bother with the potting soil, use good compost. The bagged compost is usually about as good as its price. I often buy some cheap bags if the stuff looks good, and a few more expensive bags to get better quality. Start your own compost pile too.

Also, use organic mulches. This will help keep moisture in, and they will decompose into the soil too. Preferable to use mulch that breaks down fast, like leaves, grass clippings, wood chips or shredded yard waste (these last two are often free from your city or utility tree service). Avoid the cedar, cypress, pine bark etc. bagged mulches that are rot resistant. You're not mulching just for appearance, but also for soil improvement. The potting soil/compost over the top is probably what helped your plants in front. Mulch is also very useful around perennials where you can't dig in more compost every year.

It takes a long time to get clay to behave better, but it can be very fertile soil.

    Bookmark   July 24, 2014 at 10:47AM
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What you did is basically use the potting soil as a mulch ... mulch is good, but potting soil is a mediocre mulch.

For the rest of the summer, work on adding organic material to the rear ... layers of grass clippings, the plants you pulled out ... spread it on! This fall, pile on all the dry leaves you can get and start a compost pile.

Next spring, plant back there, tilling or not, under all that nice organic material and you will be amazed at how much better things grow.

    Bookmark   July 24, 2014 at 11:29AM
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LantanaLove(9 - Riverside, CA)

Lazygardens - Yes, I used potting soil as mulch. I'm not sure why that was confusing for other readers to understand. I don't use actual top soil because I've had a lot of people swear that it's total c**p.
I figured that if my approach to using potting soil as a top soil worked so well in the front, it would work in the back too - and the organic compost would make it that much better.
We're in a rental property so I wanted something quick and easy so I can enjoy the benefits while we're still here. We plan to stay for quite a while, but I don't want to spend a ton of money and time preparing the beds for the next set of tenants. I just want some pumpkins and I want them now! :)

    Bookmark   July 24, 2014 at 1:20PM
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tropical_thought(San Francisco)

I wish I could think of a cheaper faster item. I just buy bagged wood and make my own compost, but it's not fast and if you buy bins it's not cheap either. But, the plain wood is cheaper then buying pricey bags of so called compost, which may not be that great. You have to read the
ingredients list. They used to sell a bagged product called Clay Buster, but it was expensive and they don't sell it anymore around here. It was mostly peat moss. The thing is if you read the label you can then buy the ingredients separately. For example just peat moss is cheaper then clay buster and just peat moss is cheaper then miracle grow potting soil, which is also mostly peat moss with some perlite thrown in for good measure. But you can buy perlite and everything separately instead of spending more to have a company put it all together and give it a catchy name.

    Bookmark   July 24, 2014 at 1:47PM
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nil13(z21 L.A., CA (Mt. Washington))

We are going into the height of summer which is the worst time to plant pretty much everything especially seeds. Wildflowers will be the next seeds to plant and that is in November.

    Bookmark   July 24, 2014 at 2:29PM
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nancyjane_gardener(Zone 8ish North of San Francisco in the "real" wine country)

If your clay is anything like mine, there is about a 2-3 week time that you can dig in the spring and again when the fall rains start (if they do!) during the summer months, the clay is like concrete, and even soaking with water can take a week to dig a hole (think about what those poor roots are thinking!)
However! Whenever I move my compost bin, the ground beneath is totally diggable, even in summer!
But being a renter and not willing to do the work, I would suggest container gardening. Build/buy large containers (check out CL or freecycle!) Check on the container gardening or the garden junk forums for some creative ways, or buy some concrete blocks to make raised beds to fill with soil from your landfill (cheap) or garden center.
Even your pumpkins can be planted in a 3x3, box on the ground filled with the right stuff! (you need plenty of room for them to spread, though!)
I do most of my gardening (vege) in raised beds lined with hardware cloth due to gophers, but it's not too expensive to find some wood somewhere, make a box and fill it with good soil/compost mix.
For the flowers, you can soak the ground (as I said, with our horrible clay it doesn't help much), make a 4" border, mound the soil up to 5-6 " (it will settle) and plant your annuals.
And so I ramble HTH! Nancy

    Bookmark   July 25, 2014 at 2:17AM
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As pointed out previously, potting soil makes a lousy mulch and it is far too expensive a product for that purpose. Potting soil is intended for "potting" or growing plants in containers and focuses minimally on organic content but heavily on fast drainage and aeration.....factors which are counterproductive for a moisture retentive mulch.

The suggestion of focusing your methods on container gardening is a good one. It is far easier to tailor or purchase soils specifically for container culture than it is to attempt to modify inground garden soil. Plus you have the benefit of being able to take it with you when you relocate rather than leaving all your hard work for the landlord's benefit. And remember that anything grown in the ground can be grown in a container as well :-)

If you DO choose to improve your garden soil, focus on compost, whether you decide to expend the effort to work it into the soil or merely use as a top dressing or mulch.

    Bookmark   July 25, 2014 at 2:37PM
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tropical_thought(San Francisco)

I agree, if I was only renting I would never have bothered to amend my soil. I feel like now I can never move as I am not young enough to ever do this again to a new soil area. It took 20 years of labor to get the soil, so its all nice and not hard compacted sand. And the cost was in buying bin and buying things to use to make compost like bagged wood. I estimate, I spent hundreds of dollars on compost related costs, maybe thousands? Trips to Starbucks for coffee grounds, car cleaning then the bags exploded in the trunk.

    Bookmark   July 26, 2014 at 9:00PM
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