Most gardeners today are aware of the dangers of chemical use in the garden. Whilst many of the harsh chemicals we once used are no longer available, and a lot of the newer products are generally safer – we still tend to rely on them too much. Nevertheless, there are a lot of things you can do to avoid problems without using chemicals. Most of these measures involve making informed choices about what plants you grow and managing the soil and environment in which they grow.

There are lots of things you can do but whatever you decide, it can’t be a ‘one-size-fits-all’ approach. That won’t work – your approach should be integrated and diversified: 

Soil is the first and most important aspect to attend to. There are many ways you can improve your soil: 

Some plants are more susceptible to pests and diseases than others. Using problem plants creates problems. However, plants that are problematic in one place might not be a problem elsewhere.  
 
There are many cultivars, of many species, that are more disease resistant. For example, roses are very prone to blackspot, but many newer cultivars are resistant. Check out which pests and diseases are common in your locality and choose species that are less susceptible to them.  
 
Weeds are seen as problematic – but a weed is just a plant growing where it isn’t wanted. Consider, all weeds are indigenous to somewhere. Wildflowers usually grow in harmony with the ecosystem in their natural home, and they attract pollinators. 

When you grow a lot of the same plant together, the visual effect may be good. But if a pest or disease invades a mass planting, it can quickly damage everything. When lots of different plants are grown together, it is far less likely that any one pathogen can devastate all the plants. This is because the plants which a pathogen species attacks are often within the same genus, or even family. If you mix plants from different families in a garden, you will lose fewer plants to a specific disease. 

You cannot easily change the existing microclimate of an area. The walls and fences that stop airflow will always be there, and the soil, slopes and drainage will only change very slowly over time. Similarly, light and temperature conditions tend to change slowly as plants grow or die.  Be mindful of these things. Consider how these subtle changes might occur. Choose plants that are suited to the prevailing conditions and resilient enough to adapt to future changes and still grow well. Use a range of plants that grow well in similar environmental conditions.

Controlling pests and diseases without harsh chemicals requires a little more thought. Whilst aphids may be effectively controlled with a toxic poison after they have swamped your plants, softer options like traps and predatory insects might only work if used continually to prevent pest populations exploding. 

Pathogens, like other living things, have preferred environmental conditions and patterns of growth. If you understand their lifecycles, you can control them by doing something to break the lifecycle and attack them when they are most vulnerable. If you understand their preferred environments, you may be able to disrupt that environment e.g. avoid splashing water onto plant foliage or remove leaf litter from the ground and compost it before returning to the soil.  

Different plants prefer different soil conditions. Some need constant moisture whereas others prefer free-draining soil. Some tolerate extreme wet or dry. Some need very fertile soils, but others grow in poor soils. Every species is different.  
 
Species grown in optimal soil conditions for their needs will resist diseases and be healthier. Choose appropriate plants to match the soil, then manage the soil with mulching, watering, and feeding as required. 

 
Right plant right place - if you want to grow plants that are unsuited to the locality be conscious that this is a challenge. It may require more effort, cost, time and knowledge to achieve good results. Challenging plants are so-called for a reason. 
 
Encourage beneficial insects - biodiversity (discussed earlier) can also be used to attract ‘beneficial’ insects some of which predate on pest species. Create a diverse planting scheme using a range of annuals and perennials in the garden to provide a ‘home’ for fauna such as insects, birds, and frogs which control insect pests.  
 
Companion planting – a method that is used to enhance and improve the health of plants living alongside each other. Although not scientifically proven, companion planting is used by many gardeners who claim it improves the health of their gardens.  It also helps to create biodiversity by using a range of different companions. It can be used to attract pollinators and repel pests from crops (Calendulas are often used for this purpose). Mustard is used as a natural soil fumigant when dug into the soil.  
 
Crop rotations – a sustainable garden practice to improve soil health. If you consistently plant the same crop in the same space, it can encourage a build-up of pests and diseases because each crop attracts certain enemies. Rotations prevent the build-up of pests and pathogens. They also help maintain soil fertility. Since each crop has specific nutrient needs, rotating crops avoids depleting certain soil nutrients. Include occasional deep-rooted crops in rotations to improve soil aeration and use nutrients lower in the soil profile.  
 
Mulching – using organic mulch on top of the soil helps to conserve water, encourage soil life, and keep the soil cool or warm depending on the season. The right mulch – such as pea straw, compost, lucerne hay – can improve soil structure, texture, and health over time. This boosts plant health making them less prone to pathogens and insect attack.  
 
Soil solarisation - a method that can be used to kill some soil pathogens (e.g. verticillium wilt) and weed infestations. The soil needs to be damp and covered with clear plastic for around 2 to 3 weeks during sunny weather. This kills pathogens in the top 7 – 10 cm of the soil (can be harmful to beneficial soil life, but recovery is usually fast).  
 
Row covers - a simple but effective way to exclude certain pests such as cabbage white butterfly. Use a fine mesh to deter these pests.  
 
Garden hygiene - clear debris, gather and compost leaf litter, remove non-diseased crops after harvest and compost them, remove or prune diseased plants and destroy, remove snails and slugs.  
 
Natural sprays – there are many alternatives to chemical treatments available.  Alternatively, make your own – there are many recipes available online. They include neem oil, garlic oil, baking soda, chilli pepper, or diatomaceous earth. To avoid unwanted damage, only use proven recipes. 
 
The best methods focus on creating a balanced ecosystem within the garden to naturally support plant growth and prevent pest and disease issues. 

Rosa Bonica, a floribunda rose with resistance to black spot. Many roses are resistant to black spot, and others are not. Avoid red and yellow flowers, and hybrid T roses if black spot is an issue. 

Aloe Venus  Aloes are super hardy plants that can grow well from Southern to northern Australia, don’t need particularly good soil conditions and will flower wherever they can get direct sun for 6 or more hours a day. They also attract birds which can help control pests. Choosing plants that grow easier, with less attention like this can help increase biodiversity too, reducing the likelihood of issues with other plants.

Bromeliads don’t require any great depth of soil to grow; and don’t tend to get many health issues unless roots are sitting in water and begin to rot. Some are susceptible to foliage burn in direct sunlight. Those with spiky edges are often more tolerant to stronger light.

There are all sorts of deterrents that can be used to reduce the incidence of pests attacking plants. Rough surfaces such as diatomaceous earth, wood shavings or wool waste are uncomfortable for snails and slugs to crawl over.

Prepare the soil well and the chances of later problems reduce.

Better soil quality keeps plants heathier.

Biodiversity in a vegetable patch.

Netting keeps cabbage white butterflies laying eggs on brassicas.

Row covers to keep pests at bay.

Not all insects are bad, this one can attack and eat plant pests.

Solarisation can be used to destroy pests and diseases in soil before planting.