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help w/ clay soil and penstemons, crocosmia, etc.

Posted by aimeekitty 9-10 SW 18 (My Page) on
Sun, Aug 21, 11 at 1:53

Hi folks! I'm a beginning gardener. We started our garden from scratch in Dec '09. It's clay alkaline soil. We're zone 9/10, SW 18. inland socal.

Last year I had pretty good luck with penstemons all through the summer (which is pretty dry here, but I give them some garden water) but then in the winter, I think they rotted.
Is this just an issue of me not amending the ground enough to get better drainage? I know my drainage is poor, but I do try to amend with pumice and compost and "amend" and that sort of thing. Maybe plant even higher, and perhaps put rocks around the higher area to try to get the soil to stay in a berm to help them drain better?
I really like them, so I'd like to figure out how to get them to work better for me.

Also, all these crocosmia,... why are they looking sad? :( I amended the soil so much!


Follow-Up Postings:

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RE: help w/ clay soil and penstemons, crocosmia, etc.

Oh, frustrating!
How deep are you digging in your amendments? Do you know if your area has a hardpan underneath? I find hardpan in some areas, it's often at least a foot below the soil, and it has to be dug with a pickaxe.
If you don't want to dig, then you are absolutely right that raising the area can work well. I must say that I have over amended my soil in some areas. It is so well draining that I made it very dry. If you aren't sure what is the best thing for amending your soil, perhaps your extension service can give you some ideas...


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RE: help w/ clay soil and penstemons, crocosmia, etc.

Well you need to amend your soil so it gets to a 7 ph. As it is alkaline I would suggest you stop putting in pumice. Just curious, why use pumice? It would also be useful to know if you have hard or soft water.

You say the soil is hardpack clay and that drainage is an issue. Yet it looks rather dry. I'm guessing it's too hardpack and water is just rushing down.

You could fix the soil by using the double digging method. Use triple mix soil to amend your garden bed. It will instantly fix the bed although it is labour intensive. Double digging involves digging a hole, adding the new soil, digging another hole and putting the dugged out soil into the first hole, mix it with the new soil, add the new soil into this new hole, then dig yet another hole and put the soil in the previous hole. Do this until the entire bed is dug up and new soil is mixed in.

The above will help to create drainage and fix the PH.
Do check the PH to try to get into the median (7). You can get testing materials from Home Depot or the like.

Use bonemeal to add phosporous to the bed too.

Ianna


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RE: help w/ clay soil and penstemons, crocosmia, etc.

I'm feeling very frustrated. My roses are doing great, as are the lavender, yarrow, irises, lambsear, lantana and some other things... but somethings that SHOULD do fine according to their zone requirements (and water requirements) just seem to utterly fail and I don't know if it's because the plant is wrong for my area, or if I'm doing something wrong.

But I posted this thread because I was reading a gardening magazine that AGAIN recommended crocosmia as a clay tolerant plant, one of the reasons why I planted them.

which makes me think that I'm doing something wrong.

digging up the entire bed isn't really feasible at this point as there's lots of plants in it, including roses that are doing fine! I WANTED the landscapers to do that when they put the bed in to begin with, but they did a lot of things wrong and now I'm to the point I am now.

my local nursery told me to put in pumice to aid with drainage, which I'm assuming is an issue with stuff like penstemons and crocosmia.

I basically try to dig out a hole at least twice the size of the plant when possible... then I refil it with the soil mixed with half gardening/bagged soil and some compost or "amend" and some pumice. Since I'm adding that in there, (and then the plant itself of course takes up space) the soil raises the ground level there. But with the crocosmia, I tried to dig up a large area and raise it several inches on purpose and then plant the bulbs. I also did this in a large area for my cosmos, since there was nothing there, I was able to.

all this is backbreaking though because there's still a fair amount of rocks hiding and various spots are extremely hard to dig in. I'm not sure if we have hardpan, but the clay varies and sometimes I do need a pickaxe to dig.

Is there some way I can get someone to come out and analyze my spot and tell me what I'm doing wrong without this visit costing hundreds of dollars or something?
I'm not sure if I trust these landscaping guys (or other landscaping guys) to KNOW what to do or even to tell the truth. A previous one wanted to put berms around my lavender, which I don't think is right (lavender like pretty sharp drainage, right?)


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RE: help w/ clay soil and penstemons, crocosmia, etc.

Aimy don't get too frustrated. This is actually how we all learned to garden.

Instead of digging up the entire bed, I would suggest another technique. With any garden implement, punch in as many holes as you can around plants etc.. I like using a my large garden fork for this purpose. The fork will actually help to break up hard surfaces. Now mix in more of that new soil. it will work, I promise you. If there are spaces you can dig up -- I would still recommend the double digging method. Perennials do require a minimum of 6 inches or more of good soil so probably if you can amend a bed to 1 foot deep, it would be good. It doesn't have to be all that but as you go along working on this bed, do this task gradually. Little bits at a time. Some folks will mix in their kitchen compost directly into the bed - but you need to take care that such things do not attract pests like raccoons.

To soften clay (I have clay too) use a mix of 2 things. Brick sand and triple mix top soil. Brick sand or cement sand can be found in any garden centre. I assume it's much more cheaper than pumice. (Perhaps pumice is more widely available in your area, if not, I think your nursery just wanted to sell you the more expensive alternative) You need to dig this mix into the soil. It doesn't work by just layering it on top. I alos like to amend using peat moss however without knowing the garden's PH, I hesitated to recommend it. Do not over do any of the mix. Don't use play sand. Sand & clay = cement. Sand, triple mix, peat moss +clay = a great bed.

The thing about clay is that it holds plenty of good nutrients. It's just getting the bed aerated enough so roots can penetrate it and oxygen can get to the roots. So breaking the soil is probably your most important task to do.

Take as many photos of the yard as you can, even where the plants are thriving so we can see what's happening. There may be other factors we just don't see in the one photo you provided.

The plants you have mentioned like lavenders etc.. will do well in harsh circumstances. I have lavenders growing in aspalt cracks. These mediterranean plants are known to survive in rockery areas under very dry conditions. My lambs ears are also similarly tolerant.

The crocosmia is browning at the tips, meaning it hasn't received as much water in the spot. Perhaps that's a clue. Perhaps water is rushing out too fast that it doesn't get absorbed in that very spot. Or perhaps you added some fertilizers that burned the roots. Have you been fertilizing BTW?

Ianna


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RE: help w/ clay soil and penstemons, crocosmia, etc.

Thanks, Ianna, I really appreciate the in depth response.

Maybe I amended the area the crocosmia were in TOO much so that they aren't getting enough water...?

what is triple mix and where can I get it?

I fertilized this spring and haven't since. I'm assuming I should fertilize again this fall?

I took a lot of photos of my back yard this morning to help explain my situation better, I'd be very grateful for any direction you can give me. This fall when it starts to cool down I'm really hoping to improve things.

please see link below.

Here is a link that might be useful: PHOTOS AND EXPLANATION


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RE: help w/ clay soil and penstemons, crocosmia, etc.

Aimee, I think you are not watering enough for some plants and too much for the crocosmias. Crocosmias like to be on slopes where they get almost no water. I would just throw in the towel with crocs and penstemons, since they are troublemakers for you. I couldn't keep crocosmias alive here in Simi either, but they grew like weeds at my college dump in the hills of Highland Park, where they were never watered.

Twenty minutes a week in the summer here is not enough water, but my soil drains and yours does not. You should dig down with a screwdriver to see if the soil is moist. As you know, once your clay dries out, it is very hard to get it wet again. I would say thirty minutes a week is minimum. I water forty minutes a week (20 min 2X)in the summer at a minimum, and my zone is one step less extreme than yours. I think Hoovb waters 3x a week in summer.

Oh, and your soil is not soil, it is the subsoil exposed when the developers graded away the topsoil to make the lots on the hillsides there. Many gardeners say to forget about amending the subsoil. My mom amended her sub-soil for thirty years and it didn't do a thing. Once plants get established, though, they do well as long as they are getting enough water.

Fertilizer is weird here too. The alkalinity prevents plants from taking up phosphorus and other trace elements, so some experts say save some money and don't bother with anything but nitrogen in SoCal clay. You can get the soil tested to see what it lacks. There is nothing to be done about the alkalinity. It is in our water. You would have to use bottled water in the garden.

If it was my garden, I would mulch heavily with compost (assuming money is no object and you have a strong back). Keep the mulch away from the irises. Ditch the non-performers, unify your plantings by choosing a few dominant groundcovers like lamb's ear, Santa Barbara Daisies, and lantana. Each garden is its own universe, and we can only learn its ins and outs through trial and error. You are a great gardener. It's the magazines that are wrong!
Renee


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RE: help w/ clay soil and penstemons, crocosmia, etc.

I can see now why you've had so much problems. You live in desert like conditions. That soil looks like it's been filled with builder's backfill. It's quite limey. Given that its a rather challenging area, I would suggest looking around your neighborhood to see what thrives and use many of those plants. Roses and lavenders will thrive in your area, as do lamb's ears. Crocosmia is already borderline in a zone 9 and you mention being closer to zone 10. It is also tolerant of mildly alkaline soil. That the plant is suffering is probably a good hint that it's not coping. You could replant it in a container if you like crocosmias that much.

I would suggest that you try out an experiment. Water as you would normally. Wait for 10 minutes and dig a hole. See if the water penetrated. If not, it tells you water isn't reaching below surface and so you will need to break up the soil and amend with organic soil like triple mixes. You may also consider drip irrigation - the system is easy to set up. You can find these in online catalogs like Lee Valley tools.

Here's a little bit of info I obtained about alkaline soil...What Causes Soil to become Acidic or Alkaline?
1. Parent Material - Soils are made up of ground up rock and the type of rock dictates the natural pH of the soil. Basic rock like limestone creates alkaline soil and acidic rock, with acidic rock, rock containing more silica, creating acidic soil.
2. Rainfall - Rain leaches basic elements such as calcium and magnesium from the soil. Therefore you will find areas with high rainfall generally have acidic soil while dry areas tend to have alkaline soil. In fact the work for deserts in Arabic is al khali.

3. Fertilizers - Some fertilizers tend to make the soil acidic. Ammonium urea is an example.
How Does Soil pH Affect Plants?

Most plants like a soil pH close to neutral or just a little on the acid side. A very high or very low pH can be toxic to the plants.

In Acid soils calcium (Ca), and magnesium (Mg) are less available to plants. Aluminum (Al) and manganese (Mn) may reach toxic levels. Phosphorus is tied up by iron (Fe) and aluminum (Al). Bacteria grow poorly as well.

In Alkaline soils phosphorus (P) gets tied up by Ca and Mg. Iron (Fe), zinc (Zn) and manganese (Mn) are less available. Sometimes excess salts accumulate and potatoes are subject to bacterial diseases.

How Does Compost Help?

Compost is useful to add to soils regardless of whether you have acidic and alkaline soil. How can it do this? Compost is a buffering agent.

A buffer is a substance that tends to lessen the change in pH. Compost allows the soil pH to effectively range to one point above and below the pH reading for your soil. So for example, for me with a pH of 8 adding compost gives me a range of 7 to 9 pH. As 7 is in the ideal range for plants I've solved a good part of my pH problem with the compost.

How to Lower the Soil pH of Alkaline Soils
I've found that many gardening sites and books throw up their hands in defeat when faced with soil pH in the alkaline range. Personally I think it's that there are fewer people here in the dry areas where soils tend to be basic. These garden experts are not terribly motivated to solve this problem because they don't happen to have any experience of it. So they simply write soils with high pH off as impossible.

So - please do your soil tests before you try to fix your soil and then go slow in effecting changes. Give your soil biology a chance to adjust and adapt to the new conditions.

Your first line of action is compost. It does work to change the actual pH and to minimize the difficulties arising from a high pH.

To lower your soil's pH sulfur is your friend. It takes very little but it takes some time. The equation is sulfur + time + soil bacteria = a lowered pH. Again you will need less sulfur in sandy soils than in other soils so know your soil texture. Follow the directions that come with the material you purchase and don't try to change things more than one pH point per season."


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