Planting in difficult conditions Part 1 – Clay Soils

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We get a lot of questions from our customer but one of the most common type of question we get is “will this plant cope in certain conditions”. Clay\sandy soils, coastal positions, high wind, frost, dry areas and shaded positions all take their toll in varying degrees on each variety of plant. We’ve put together a series of tutorials to you show how to deal with these difficult conditions and which plants may suit a given condition.

The first in this series will be dealing with difficult soils. We’ll talk about clay soils and how to improve the condition of your soil to get great results. This is by far the most common problem we get asked about.

Contrary to popular belief, clay itself can be very good for plants, it contains an abundance of nutrients that plants can use to thrive, the problem is that it doesn’t allow water to drain away from the roots. Most plants don’t like to sit in wet, boggy soil so clay will cause all sorts of problems.

The best course of action is to choose plants that are clay tolerant and will thrive in such conditions, such as the varieties listed below. But if you’ve got your eye on a variety that’s not so suited to clay, don’t despair, there are things you can do to improve your soil to allow for such plants. What you need to do will depend a lot on the type of clay you have and how much work you’re prepared to do to remedy the problem.

Testing

There are quite a few different tests you can do to work out what type of clay you’re dealing with but for the purpose of this tutorial, we’re going to try to keep it as simple as possible.

The first thing is testing for texture. Take a small lump of clay from your garden and add some water and work it in like you’re going to use it for pottery. Roll it into a ball in your hand. Next, flatten out between your fingers in the shape of a ribbon, if you can flatten it to more than 50cm before it starts breaking up then you have a heavy clay.

Another test is the percolation test, this will determine how compacted the clay is. First dig a hole about 60cm deep and 30cm wide. Fill the hole with water and let it drain out completely. Once it’s empty, fill it again and take note of how long it takes to drain out. If it takes less than 12 hours to drain, the soil should be able to support plants that require well draining soil. If it takes 12-24 hours to drain, the soil is best suited to plants that tolerate heavy or clay soils. If it takes more than 24 hours for the hole to completely drain only trees that withstand occasional flooding will survive.

Note: If you find Earth worms in your soil, then this is usually a great indicator of healthy soil

Action

The aim is to improve soil structure by breaking down the clay to achieve looser, more granular particles and allow water to drain away but at the same time retain moisture and nutrients. The best way to do this is add as much organic matter as possible and as deeply as possible to the clay. Organic matter doesn’t only add to the nutrient content of the soil, it coats the clay particles and physically separates them from each other.

Another option is to add Gypsum to the clay to help break it down. This is somewhat less effective as not all clay types respond to Gypsum but there is a way to test it. Remove a small sample of clay from the garden and place it in a glass jar with clean water in it. Don’t touch the jar but take note of the water after an hour then after 24 hours. If the clay begins to disperse in the water making the water cloudy then your soil will respond to Gypsum, the cloudier it becomes the better the Gypsum will work. Gypsum can be added to the soil at a rate of around 1kg per square meter and should be worked into the soil, it would probably be a good idea to add in some organic material such as compost while your turning the soil.

Of course the best course of action is to try and find plants that will thrive in clay soils. Here is a list of suggestions we’ve found work. Some of these we sell on our site, some we don’t.

Groundcovers
Brachyscome Multifida (Cut-Leafed Daisy)
Campanulas (Bellflower)
Grevillea Curviloba (Curved-Leaf Grevillea)
Grevillea Lanigera (Woolly Grevillea)
Hosta varieties (Hosta)
Polygonatum hirtum (Glossy-Leaf Solomon’s Seal)
Rhodanthe anthemoides (Chamomile Sunray)
Viola hederaceae (Native Violet)

Small Shrubs (Up to 1m)
Berberis thunbergii (Japanese Barberry)
Eriostemon myoporoides (Long-leaf Waxflower)
Grevillea Poorinda Royal Mantle (Grevillea Royal Mantle)
Grevillea Robyn Gordon (Grevillea Robyn Gordon)
Grevillea Gingin Gem (Grevillea Gingin Gem)
Myoporum montanum (Emu Bush)
Prostanthera rotundifolia (Round-leaved Mintbush)
Prostanthera ovalifolia (Purple Mintbush)
Prostanthera Poorinda Ballerina (Mint Bush)
Westringia fruiticosa (Coastal Rosemary)
Westringia Wynyabbie Gem (Westringia Wynyabbie Gem)

Medium Shrubs (Up to 3m)
Banksia marginata (Silver Banksia)
Banksia ericifolia (Heath-leaved Banksia)
Banksia spinulosa (Hairpin Banksia)
Banksia robur (Swamp Banksia)
Baeckia virgata (Tall Baeckea/Twiggy Heath Myrtle)
Buddleia (Butterfly Bush)
Callistemon citrinus (Crimson Bottlebrush)
Cercis canadensis (Eastern Redbud)
Dodonaea viscosa purpurea (Purple Hop Bush)
Alyogyne huegelii (Lilac Hibiscus)
Grevillea victoriaea (Royal Grevillea)
Grevillea rosmarinifolia (Rosemary Grevillea)
Grevillea Superb (Grevillea Superb)
Grevillea Ivanhoe (Grevillea Ivanhoe)
Hakea laurina (Pincushion Hakea)
Jacksonia scoparia (dogwood)
Kalmia latifolia (Mountain-laurel)
Kunzea ambigua (White Kunzea, Poverty Bush or Tick Bush)
Leptospermum laevigatum (Coastal Tea Trea)
Melaleuca decussata (Totem Poles)
Melaleuca nesophila (Showy Honey-myrtle)
Melaleuca hypericifolia (Honey Myrtle)
Melaleuca Gibbosa (Slender Honey Myrtle)
Prostanthera lasianthos (Victorian Christmas Bush)
Syringa varieties (Lilac or Common Lilac)
Thuja Occidentalis – Hetz Midget (Dwarf Northern Whitecedar)

Large Shrubs and Trees
Aesculus hippocastanum (Horse Chestnut)
Acacia Floribunda (Gossamer Wattle)
Acacia Baileyana (Cootamundra Wattle)
Acacia Howittii (Sticky Wattle)
Acacia Melanoxylon (Australian Blackwood)
Agonis flexuosa (Willow Myrtle)
Betula nigra (River Birch)
Callistemon viminalis (Weeping Bottlebrush)
Callistemon salignus (White Bottlebrush)
Callistemon King’s Park Special (Hybrid Bottlebrush)
Eucalyptus forrestiana (Fuchsia Gum)
Eucalyptus leucoxylon (Yellow Gum)
Grevillea robusta (Silky Oak)
Hymenosporum flavum (Native Frangipani)
Leptospermum petersonii (lemon-scented teatree)
Magnolia soulangiana (Japanese Magnolia)
Malus John Downie (Crab Apple)
Melaleuca diosmifolia (Rosey Paperbark)
Melaleuca armillaris (Bracelet honey myrtle)
Melaleuca linarifolia (Narrow-leaved Paperbark)
Melaleuca squarrosa (Scented Paperbark)
Melaleuca ericafolia (Swamp Paperbark)
Pyrus calleryana ‘Bradford’ (Bradford Flowering Pear)
Syzygium australe (Brush Cherry Lilly Pilly)
Thuja Plicata (Western Red Cedar)

Grasses
Carex Oshiemensis Evergold (Variegated Japanese Sedge)
Hemerocallis varieties (Daylily)
Dianella Tasmanica (Tasmanian Flax Lily)
Dianella Revoluta (Flax Lily)
Isolepis nodosa (Knobby Club-rush)
Lomandra longifolia (Mat Rush)

Climbers
Billardiera longiflora (Purple Appleberry)
Hardenbergia violaceae (Happy Wonderer)
Pandorea Jasminoides (Bower of Beauty)
Pandorea Pandoreana (Wonga Wonga Vine)
Sollya heterophylla (Bluebell Creeper)

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