Clay soil can be both a curse and a blessing. It’s naturally rich in minerals but often sticky in winter, hard as concrete in summer, and easily waterlogged. The right plants will persist and thrive in clay so we've made a guide at the end of this article.

For Northland gardens where clay is common, the key is learning how to work with what you’ve got, steadily improve it over time, and in the meantime work around its limits so you can still grow successfully. Of all the 3 main soil types (sand, clay, silt), clay soil consists of the tiniest and densest particles which can lead to drainage issues and easy compaction.

Healthy soil is a dynamic mix of air, water, minerals, and organic material from plants and animals - both living and long gone. These elements fall into two key groups. The biotic components are the living and once-living parts of the soil, like roots, microbes, and insects. The abiotic components are the non-living elements, such as minerals, water, and air. Among the minerals, nitrogen, phosphorus and potassium are the big players that fuel plant growth, while smaller but still important amounts of calcium, magnesium, and sulfur help keep plants healthy. Together, these living and non-living factors create the unique composition that makes each soil thrive.

How to Identify Clay Soil

Many of the hills in around Northland are clay bases as a start. If your land gets mushy in winter but rock hard in summer, you've probably got clay soil. If you dig down past any compost and surface material, you may notice a relatively uniform texture and colour, if you've felt clay around a pottery wheel - this isn't much different. Clay soil is:

• Heavy and sticky when wet.
  - Cracks and sets hard in dry spells.
  - Water puddles on the surface instead of draining quickly.
  - When rolled in your hand, clay soil can form a sausage shape that doesn’t break apart easily. There's not too much difference between the texture of your clay in your soil and some you may have played with in a pottery class.
  
  You can click the links below for the Soil Type Map Tool here as a broad starting point for your property but remember that your property is likely to be unique with its own soil makeup that differs slightly.
  
  - Mangawhai-Warkworth (Bream Tail to Mahurangi)
  
  - Maungatoroto-Kaipara (inc Langs, Waipu)
  
  - Hukerenui-Whangarei (Ruakaka, One Tree Point, Whangarei Heads)

Garden Tip: If you can't beat 'em, build 'em and fill 'em. Raising your garden with planter boxes or hard landscaping features then filling with well draining garden mix is just one way to work around clay soil quickly.

Clay Soil Planting Solutions; Working With What You’ve Got

Clay holds nutrients well, so you’re starting with fertile ground. To make the most of it:

• Plant into raised ridges or mounds to improve drainage around roots.
  
• Choose tough, clay-tolerant plants to tart with such as pōhutukawa, cabbage trees, camellias, citrus, feijoa, apples, and plums. Hedging plants like griselinia, pittosporum, or viburnum also cope well. Many leafy veges like silverbeet, kale, and broccoli can handle clay with some preparation.
  
• Mulch thickly with organic matter to keep moisture steady and stop the topsoil baking hard. Autumn leaves, grass clippings, manure, worm castings, compost and any almost organic matter in small pieces you can find will help change the composition of the soil over time and create a microhabitat for your plants.
  
• Time your digging. Work the soil when it’s moist but not sticky. If it clings to your spade, wait.
• Aerate your clay soil when its soft - note you should be using a fork tool that pokes holes rather than tills your soil - tilling can actually make the soil worse if done incorrectly by compacting it.

Above Image: Take a long term approach to increasing organic matter to the soil and let nature do a lot of the hard work for you by planting deep-rooted cover crops and hardy pioneed species that deposit leaf litter over time. Each time making gradual changes to ensure the success rate of the next stage of planting.

How to Improve Clay Soil Over Time

Clay soil can be transformed over time into rich garden loam:

• Add organic matter often. Compost, rotted manure, leaf litter, or lawn clippings build humus that opens up the clay.
  
• Grow pioneer species. Plants like tagasaste, kōwhai, and fast-growing wattles drop leaf litter that slowly changes soil structure.
  
• Use cover crops. Lupins, mustard, and oats punch roots into the clay, break it open, and add organic matter when dug back in.
  
• Dig trenches and refill. For new trees or shrubs, dig a wide trench and backfill with compost-rich soil to create a “basin of niceness” for roots to establish in before hitting heavier clay.
  
• Think in decades. Every season of mulching, planting, and composting chips away at the density until the soil is more forgiving.

Above Image: Cross section of a trench, essentially this could be a trench with gravel chip or scoria through it but wrapping the geotextile around the chip with a drainage pipe will be a more robust long term solution that doesn't get clogged as easily.

How to Work Around Having Clay Soil Immediately

Sometimes improvement takes too long or isn’t practical for every corner of your section. That’s when you can bring in the big guns and why smart workarounds matter:

• Raised beds. Import good soil or mix in compost, and keep the growing zone above the sticky subsoil. Perfect for veges and strawberries.
  
• Bunds and berms. For landscaping, build up soil into low ridges or mounds to plant into, keeping roots above the wettest clay.
  
• Drainage trenches. Simple “soakaway” trenches filled with scoria or stones let excess water move away from plant roots.
  
• Planter boxes, pots or tubs. For plants you want to keep out of the clay like sensitive crops (like blueberries or capsicum), skip the clay altogether and use large pots with premium mix.

Preventing Compaction in Clay Soils

Clay structure is fragile and once it’s squashed, it stays that way. Once you've put all this effort into improving and transforming your garden bed, don't squash your progress by trampling over your garden. Protect it with these habits:

• Don’t work wet clay — wait until it’s crumbly, not sticky.
  
• Lay down planks or boards when walking or moving gear across the soil
  
• Create permanent paths with gravel, woodchip, or stepping stones to direct foot traffic
  
• Avoid heavy vehicles on wet ground - keep to one track if you must drive.
  
• Keep vege beds “no dig” with permanent paths between them. Over years, those untouched beds will loosen while the paths carry all the weight.

Above Image: Landscape Designer Jeremy Levine shows this meandering partly paved garden path - Use pavers, defined pathways or temporary boards to limit compaction while moving around your garden to improve the Clay Soil by limiting compaction of it.

Plants That Thrive in Northland Clay Soils

Here's our tried and true shortlist of plants for Clay Soil in Northland - There are plenty more that suit clay, especially if planted on a slope or raised mound to keep the roots 

Groundcovers & Low Growers

• Hebe species (NZ) – tough native groundcovers and small shrubs; tolerate clay well.
• Coprosma kirkii, Coprosma acerosa – native ground-hugging forms, stabilise clay banks.
• Prostrate Coprosma repens 'Poor Knights' (Mirror Bush, NZ) – glossy leaves, thrives in exposed clay sites.
• Ajuga reptans (Bugleweed, exotic) – forms dense mats, good under trees in moist clay.
• Thyme, Oregano & prostrate Rosemary (herbs) – aromatic groundcovers, best on slopes or free-draining clay.
• Grevillea groundcover forms (exotic) – hardy Aussie natives, need free-draining spots like banks or raised beds.

Above Image: Prostrate Rosemary is a fantastic addition to clay banks, rocky walls and as underplanting in sunny areas on clay soil

Grasses, Flax & Strappy Plants

• Phormium tenax (Harakeke / NZ Flax) – thrives in heavy clay, wet or dry, dramatic foliage.Phormium cookianum (Wharariki) – smaller, arching form, great on banks.
• Carex secta, Carex virgata, Carex testacea (Sedges) – excellent in boggy clay areas, stabilising stream edges.\
• Austroderia (Toetoe) – big statement grass, tolerant of clay soils.
• Lomandra longifolia (Mat Rush) – bulletproof Aussie plant, thrives in clay (even seasonally wet).
• Lomandra cultivars (‘Tanika’, ‘Katie Belles’) – landscaping favourites, tidy form.
• Dianella caerulea, Dianella tasmanica (Flax Lilies) – strappy, blue berries; cope well in clay unless waterlogged.
• Rengarenga Lily (Arthropodium cirratum, NZ) – great for shady clay banks, adds white summer flowers.
• Dietes grandiflora, Dietes bicolor (African Iris) – iris-like flowers, hardy in clay; avoid stagnant water.

Above Image: Flower of NZ Flax Harakeke Phormium tenax - one of our toughest natives and a great pioneer species to plant in clay soils when transforming bare farmland to garden to act as a shelter.

Small Shrubs & Perennials

• Hebe cultivars – colourful foliage and flowers, clay tolerant.
• Coprosma repens (Mirror Bush, NZ) – glossy leaves, thrives in exposed clay sites.
• Manuka (Leptospermum scoparium, NZ) – good for clay hillsides, attracts bees.
• Kanuka (Kunzea ericoides, NZ) – hardy native, improves soil over time.
• Lavender (exotic) – aromatic, likes clay if on a sunny slope or raised bed.
• Rosemary (exotic) – same as lavender; excellent culinary use.
• Hydrangea macrophylla (exotic) – clay tolerant in shaded, moisture-holding areas.
• Camellia sasanqua (exotic) – thrives in heavier soils; great screening shrub.
• Grevillea species: Drought-tolerant exotics, feed tūī (need free-draining)
  
• Abelia × grandiflora: Glossy exotic, fragrant flowers (happier in free-draining spots)
• Bottlebrush (Callistemon): Aussie exotic, hardy and bird-friendly.

Above Image: Hydrangea adapt to clay soils and lavish the additional moisture some landforms create. Be strategic with your plantings for maximum impact. (Miki Yoshihito)

Shelter & Large Trees

• Pittosporum tenuifolium (NZ) – fast-growing hedge or shelter; thrives in clay.
• Kowhai (Sophora microphylla, NZ) – stunning yellow flowers, clay tolerant.
• Puriri (Vitex lucens, NZ) – glossy evergreen, feeds birds; fine in clay.
• Titoki (Alectryon excelsus, NZ) – handsome shade tree for clay.
• Totara (Podocarpus totara, NZ) – handles heavy soils, long-lived.
• Eucalyptus species (exotic) – many are clay tolerant but prefer slope/free drainage.
• Casuarina (She-oak, exotic) – good for windy clay hillsides.
• Pōhutukawa (Metrosideros excelsa, NZ) – coastal native icon, happiest on slopes.
• Karo (Pittosporum crassifolium, NZ) – very tough native shelter tree.
• Rewarewa (Knightia excelsa, NZ) – native with striking red flowers, best on slope or free-draining.
• Liquidambar (Liquidambar styraciflua, exotic) – autumn colour, avoid waterlogging.
• Plane tree (Platanus × acerifolia, exotic) – urban-tough shade tree.
• Oak (Quercus robur, Q. palustris, exotic) – clay-tolerant, strong canopy.
• Alder (Alnus glutinosa, exotic) – nitrogen-fixing, great for wet clays.
• Poplar & willow hybrids (exotic) – fast shelter belts, good for slope stabilisation.

Above Image: Liquidambar trees put on a mighty show during autumn and are one of the best-looking deciduous options for clay soil, just don't put them in a gully or soggy patch like your hydrangeas!

Fruit Trees & Edibles

• Citrus (lemons, mandarins, oranges) – do well in clay if drainage is managed (raised mound or slope).
• Feijoa (Acca sellowiana, NZ favourite) – one of the best for clay, prolific crops.
• Persimmon (Diospyros kaki) – adapts well to clay soils.
• Plum & Plumcot – generally tolerant of clay, reliable cropping.
• Apples (esp. on semi-dwarf rootstocks) – good in heavier soils.
• Pears – thrive in clay, traditional orchard tree.
• Kumara (Ipomoea batatas, NZ staple) – do best in sandy loam, but can be grown in raised beds over clay.
• Chilies & Tomatoes (annuals) – fine in clay if beds are raised and amended.
• Pumpkin & Squash – clay tolerant once established, need space.
• Silverbeet & Kale – tough leafy greens that handle clay soil’s moisture swings.

Above Image: Citrus do well in Northland's climate and our clay soils often prove no challenge for them.

Palm Trees 

• Nikau Palm (Rhopalostylis sapida, NZ) – native palm, thrives in clay and shade.
  
• Kentia Palm (Howea forsteriana, exotic) – handles heavier soils in sheltered spots.
  
• Chamaerops humilis (Mediterranean Fan Palm, exotic) – slow grower, clay tolerant if not waterlogged.
  
• Queen Palm (Syagrus romanzoffiana, exotic) – fast exotic palm, prefers free-draining clay.
  
• Phoenix canariensis (Canary Island Date Palm, exotic) – rugged statement palm, avoid soggy sites.
  

Above Image: Nikau palms underplanted with Carex buchananii, Carex testacea & Poa cita.

Pioneer Species (for long-term soil improvement)

• Manuka & Kanuka (NZ) – colonise clay, improve topsoil via leaf litter.
• Tagasaste / Tree Lucerne (exotic) – nitrogen fixer, improves soil for future planting.
• Alders (Alnus, exotic) – nitrogen-fixing, soil improvers, great for shelter.
  
• Cordyline australis (Cabbage Tree, NZ) – iconic clay-buster with deep roots.
• Phormium tenax (Harakeke / NZ Flax) – thrives in heavy clay, wet or dry, dramatic foliage.Phormium cookianum (Wharariki) – smaller, arching form, great on banks.

Above Image: Manuka in bloom - These tough characters thrive in equally tough conditions and you're rewarded with flowers, bees and birds throughout summer. Try different varieties to suit the space, there are Red, Pink, White flowering types as well as dwarf types (Usually with names starting with Wiri or Nanum or a range of NZ native birds like Kiwi, Tui, Weka or Ruru etc) and prostrate varieties for groundcovers like Pink Cascade or Liliput.

Free-Drainage Notes

• Slope or raised beds are best for: Lavender, Rosemary, Grevillea, Citrus, Eucalyptus, Mediterranean palms.
• True clay-lovers that thrive in boggy sites include: Carex sedges, Phormium, Lomandra, Nikau, Hydrangea.

Above Image: It's the little things that make all the difference. NZ native Titoki not only have a beautiful leaf form, feed native birds, they can be used as a hedge or small windbreak in Clay Soil and put on an impressive display of their root flare when mature.