Clay Soil

Gardening in Clay Soil is often regarded as somewhat of a handicap by most gardeners, especially those gardeners that have preference for growing plants that do require a well drained soil. Most of the popular West Australian natives and South African Proteas that naturally grow in sand and well draining gravels and loams have a preference for soils with good drainage.

These plants are always very popular to grow as many have large, exotic, showy flowers. Therefore if you are a gardener with a liking for these plants it begs to ask the question…..can you still grow these types of plants in a clay soil?

Well being a gardener who has gardened in clay soil for over 10 years I can honestly say, yes, and basically it just comes down to following a few rules.

Firstly though can I just say this. Recently I was listening to a gardening program on the radio where a gardener asked the question about planting into a clay soil. The answer given by the gardening commentator was to dig down into the clay and try and break it up and maybe add some gypsum. Now this is not the first time I’ve heard this type of response to this question and in some respects this answer does bother me. Why? Well consider this.

The biggest problem with clay is the fact it doesn’t allow water to pass through it very easily. Therefore once you start digging into it you really do need to be prepared to keep digging all the way through the layer of clay until you find a layer of soil that is free draining so the excess water has a means to drain away. Now does this sound like a viable exercise for every plant you plant into clay soil? Not really, the hole you dig may have to be quite deep to make it effective.

Therefore once you start digging into clay all you’re really doing is providing an area for water to accumulate after rain. This is not an ideal situation. Now you must understand this, many areas of South Eastern Australia have been in drought up until recently so using the above mentioned method of planting hasn’t really been a problem as there hasn’t been the rainfall to make it a problem. Therefore many plants has survived for years planted into a hole dug into a clay soil.

At the end of 2009 SE Aust started getting lots of rain again and then all of a sudden plants that had survived the drought for years started to die and mainly it was caused by bad planting in unsuitable areas where excess water all of a sudden became a problem.

Therefore the number one rule when gardening with a clay soil or a clay subsoil is make sure excess water has a means to drain away. This also applies not only for water on the surface but below the surface as well. After all, if you dig a hole into a clay soil and then replace it with a freer draining soil, plus the root ball of a plant, do you really believe the excess water will drain away? No it won’t, the hole will just act like a bucket.

One solution to avoid this is to plant plants with smaller root balls such as those grown in tubes. In most cases these plants will quite often outgrow a larger plant anyway.

So what is the best solution for gardening in clay soil?

Well to start off with the obvious solution is to use plants that are tolerant of clay soils. Callistemons, Melaleucas and some Banksias, Grevilleas and Eremophilas all have some species and hybrids that are suitable.

But what if you want to plant plants that require a well draining soil into a clay soil?

Well the easy solution is to garden on sloping terrain. The excess water will easily drain away and not become a problem. Just make sure you don’t dig a large hole in the clay to your plant your plant.

But what if you haven’t got a sloping garden, what if it’s flat?

Well this is where planning your garden and good landscaping can come into play. Use raised garden beds and you can go about this in two different ways. Firstly you can import lots of suitable garden soil that is free draining or you can do what I did. I excavated an area of my garden and mounded the excess clay into raised garden beds. I then used compost and gypsum and hired a small cultivator and then mixed all the compost and gypsum into the clay mounds which were to form my garden beds. What I ended up with was a friable, well draining soil that I could plant all manner of plants that require a well drained soil.

Now if you decide to take this option just make sure the areas you excavate aren’t too deep. You can turn then into pathways and provide underground drainage to direct the water away from the garden beds.

Sound like too much work? Well remember this……….you only have to do it once.

The most important thing to remember though is you must provide a means for excess water to drain away. Correct landscaping is essential, whether it be natural or man made. At the end of the day though, there are many ways to go about gardening in a clay soil and not every plant will grow in clay but if you employ some of these basic principles you will great increase the number of plant you can successfully grow, in a clay soil.

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16 Responses to Clay Soil

  • Liz Willimott says:

    Hello Rebel Gardener,
    I live in Queensland just north of Brisbane and want to grow Proteas in a raised bed. The border material of the bed will be concrete blocks. Will this affect the plants which are acid loving as the concrete blocks are alkaline in nature. Liz

    • Rebel Gardener says:

      The concrete blocks shouldn’t be a problem. In fact some growers of fussy Proteaceae plants, that like excellent drainage, bury old bits of concrete as the lime can help to protect the roots from Phytophthora.
      If you live in Brisbane make sure the air flow around your Proteas is good as they don’t like hot, humid conditions.
      Just one extra point about the concrete borders ………….. The raised beds is an excellent idea but make sure the borders don’t trap the water. The water must have somewhere to escape and flow to. If the water is flowing for a short period that’s ok but if your border turns into a “dam wall” your plants will perish. This is especially critical in climate like yours.

  • aaron says:

    I dig a hole twice as big as i need then fill with potting mix and the plant. Also put gypsum on the bottom. It seems to work ok but it’s still a bit early to say.
    When the roots grow strong enough will they penetrate the clay? Or will the roots end up spiralling around in the bucket like hole?

    • Rebel Gardener says:

      It depends a lot on the plant. I only plant, plants that are suited to clay INTO clay. I make sure the hole is square to stop the roots from coiling. Plants not suited to clay, I mount up and plant ON TOP. Gypsum will only penetrate for a certain depth so in effect all you’re doing is making the hole slightly larger. Water always needs somewhere to go, especially during heavy and prolonged rainfall. You can either set your garden up so it runs away to a drain (not someone else’s property) or if you have a well draining soil it will soak into the sub soil. Clay will only soak up a small amount of moisture. The rest will just sit and cause root problems for plants that don’t like to sit in stagnant water.

  • Ally72 says:

    Hello rebel gardener I am working in the Pilbara with clay soils. Can you recommendany species inparticular that will do wellthere. The Grevillia hybrid is doingwell What would be a complimentary shrub?

    • admin says:

      Hi Ally, I dare say you get some pretty harsh conditions up there so I’d start by sourcing some Eremophilas that will tolerate clay. E Maculata variants would be a good place to start. Many bottlebrushes tolerate clay. I’d recommend seeking advice from a local nursery as at the end of the day it may be a case sticking with what you can source. Also I suspect that you’d get some fairly heavy rainfall from time to time so make sure you use raised beds or give the water somewhere to run off to.

  • kath andrews says:

    Hi rebel, we hav a heavy clay block so appreciate your wisdom, originally was going to plant strelitzias after losing 30 ixoras but decided to do some googling instead of listening to the nursery staff and now am on the hunt for eremophilas chheers ktz

    • admin says:

      Hi Kath, Recommending plants for a situation isn’t always easy as not all plants are available in all locations. I always think the best way to go is to use whatever plants you can source locally and then check them against a reference such as “Grow What Where” or “Australia’s Eremophilas”, to what is suited for your conditions.
      That’s why a recommend these books here on this site. I own them both and have found they have more than paid for themselves many times over.
      You’ll find not all Eremophilas will be suited to clay. Maculata’s should do. Other plants suited to clay are Callistemons, Some Melaleucas, Banksias from the eastern states such as ericafolia and there are loads of Grevilleas you could try.
      Remember, when gardening in clay, always give the excess ware somewhere to run off to. In you’re on a slope, that’s ideal. Otherwise if your block is flat build up some raised beds, behind retaining walls if possible. Also never build your retaining walls like dam walls. Always give the water somewhere to drain away to. Best of Luck.

  • Katrina A Veitch says:

    Hi, having read all there is about clay soil, I have a problem. I live in the sunshine coast and would like to plant a feature plant by the pool, yes in clay soil, the problem I have is there is no drainage as surrounded by the pool on two sides and a conctrete path on the other two sides. I have tried planting plants built up with good soil, but of course the water is trapped, I have lost palms, pandanus and lomandras. Unfortunately nothing can be done about surface and ground drainage. So I am looking for a plant suggestions that can handle clay. I have planted loads of natives in other areas which are growing well, almost too well, but as this is an area that is in a prominant position I would like to to be a feature. Can you please help.

    • admin says:

      What I’d do is get a large decorative pot that suits your decor and then plant something into it that is very drought tolerant. There are loads of plants such as cactus, succulents, euphorbias, agaves, yuccas etc that are architectural and make a fantastic feature. Just find a specialist nursery in your area and see what they have got. The trick is to not overplant them into a pot that is too large. Therefore if your feature pot is large just use a smaller pot inside that is suitable for the size of the plant and then over time increase the pot size to suit the growth of the plant.

  • Mel says:

    Hi, I have made the mistake of doing just about everything you have said not to do above…but (obviously) before I read this! I have planted a Blueberry Ash with a very large hole (dug by a digger) and filled with garden soil, unfortunately when I planted it we also had a huge constant deluge of rain for a few weeks, thankfully we haven’t had any rain in over a month and the tree is starting to show signs of life and has a few leaves sprouting through. I am located in inner north Brisbane and our soil is all clay. The tree is relatively large and cost $120, I really don’t want to lose it but am afraid when the rain starts again it might go backwards? I have already lifted it up a bit and filled underneath it (whilst it was raining). The only way I could increase the drainage would be to try and make a slope around it, but would that then be too high around the trunk of the tree? I don’t really want to move it now as it seems to be happy at the moment. I also have a lemon myrtle that is in a state of disrepair, I planted it – it got soaked with water, I moved it, it didn’t like the heat, I put it in a pot and moved it to a shadier spot, then tried adding epsom salts….but maybe overdosed? as it is all wilted, I don’t know whether to move it back to a sunnier spot or just hope for the best? again it is a relatively large tree :-( Big Rookie errors!!!!

    • admin says:

      Mel the number 1 rule with water and drainage is this, you always need give the excess water somewhere to run off to, especially if the soil is clay and will not let the water drain down through it sufficiently. This is even more essential in the tropics and sub tropics. This is always a problem with advanced trees planted in clay. Don’t pile soil around the trunk though as this will cause problems as well. I’d lift the tree out fill in the hole with the same clay back to the same level then build the soil up on top and plant the tree in that. Unfortunately things might be good now but problem most likely won’t go away.

  • Andrew says:

    Hi, I am living in inner north Brisbane and have very heavy clay soil. WE are doing some a back yard makeover and have a large amount of crushed gravel we are removing to lay turf. I was trying to kill two birds with one stone, improve the drainage of the semi raised garden beds and get rid of this crushed gravel.
    The idea is was to dig a deep trench alone the garden edge, bury the crushed gravel and cover it with a rocky garden edging. I was looking at lining the garden with shallow rooted plants that would hopefully be more tolerant of any extra moisture around the garden perimeter. Can you see any problems I may cause by doing this? Thanks, Andrew

    • mikeb says:

      Andrew the golden rule with drainage is you need to give excess water somewhere to drain away too. This even more important in the tropics. If you can dig through the clay to a sublayer of soil that will let the water drain deeper into the soil you might be ok. Taking into consideration your climate and high rainfall you could quite possibly be creating a problem. Your trench may simply act as an underground mote that just captures the water and causes a problem under the ground. If you get a lot of rain in a very short time it will probably fill quite quickly and then the only problem you’ve solved if hiding the gravel?

  • Sam says:

    Hi, we are planning to put in 28 advanced plants to provide screening from our neighbours. We also have the dreaded clay soil (Eastern-Brisbane) and have planned to have a digger come in and make long trenches into which we can plant, so there is opportunity for drainage. However, while one side of our house is on a slope so should work well with the trench, the other is largely level. We have planned to plant Acmena Smithii along the sloped (better drained side) and Syzygium Australe (either Reslience or Hinterland Gold) along the level side. I have read they are suitable for well drained clay soil – not sure what that really means :-) Would appreciate your comments on our plant choice for clay soil.

    • Administrator says:

      You will always get your best results when you plant small plants and let them grow naturally. However I suspect you’re probably in a hurry to make your neighbours disappear? Therefore your first consideration is this . . . . Ensure you always give the water somewhere to drain away to. Digging a trench that goes nowhere will not work. Secondly be aware that tree roots can grow into drainage when it’s dry looking for water and then block it so when it does rain it might not work anymore. You will have to talk to the nurseryman about the suitability but I suspect you might possibly have problems with the choice. I’d select something that will grow happily in clay. OR another option might be to introduce soil and make a bank the height of the rootball and then plant into that. Make sure you disturb the top of the layer of the clay so the roots will grow into it as they grow.

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