Optimum pH for Common Plants
While soil pH is something most gardeners don’t worry about, it can significantly influence your plants' productivity. Levels of pH not only affect the availability of nutrients in your soils, but they can result in stunted growth or sensitivity to disease. Nutrient deficiencies in plants may not be caused by the lack of a specific nutrient in the soil but are often due to inadequate pH levels.
What is soil pH?
Soil pH is a measurement of hydrogen ions in the soil. The pH is an abbreviation for the “power of hydrogen” and is measured on a scale ranging from 1 to 14. This can otherwise be thought of as a measurement of acidity or alkalinity. Things lower on the pH scale are considered acidic, while things higher on the pH scale are considered alkaline. The pH of 7 is considered neutral.
What is the best pH for soil?
Generally speaking, a soil pH of around 6.5 is considered the best for most cultivated fruits and vegetables. At this pH, nutrients are easily dissolved into the soil water and are maintained in a form that is accessible to plants. When soils are too alkaline or too acidic, soil nutrients are locked up into the soil particles or are kept in a chemical state that is not available for water.
This being said, some plants prefer more acidic soils. They are specifically adapted to thrive in these soils and have the proper biological mechanisms to obtain their nutrients in these soils. These are few but include plants like blueberries, cranberries, and azaleas. Some plants in nature also prefer alkaline soils, but these are not commonly cultivated species.
Thought Experiment
Consider this. Have you ever been somewhere with mineral-rich water and seen a plaque of what looks like calcium build-up on water kettles, pots, or in the sink? This plaque is hard to remove with water, but if cleaned with vinegar or lemon juice it easily dissolves. The same thing happens in soils. At certain levels of pH, soil nutrients are bound to soil particles like a tough plaque. When the soil pH is changed, this nutrient dissolves into the water where it is easily accessible by plants.
Should I worry about soil pH?
The truth is if you have a small home garden and you're using organic practices then this is not something you need to worry about. Regenerative practices like amending heavily with compost and not using synthetic fertilisers will help buffer pH disbalances. Organic matter in particular is extremely useful at buffering pH and keeping it at a healthy level. After all, most soils are generally within a range of pH that plants will adapt to.
Furthermore, soil pH is often a lot more complex than it’s made out to be. Soil is not usually a homogenous environment; thus pH can greatly vary throughout the soil profile. Even a couple of centimeters of distance can change the levels of pH. Plants too will manipulate the soil pH by releasing hydrogen ions and anions into the soil profile. This gives them access to a diverse range of nutrients only available at distinct levels of pH. Thankfully, this is not something you need to worry about because the plants do all the work!
When To Consider Testing pH
+ Before planting your garden bed to gain an understanding of your soil’s health.
+ If your plants look unwell, despite knowing they’re receiving adequate water and nutrition.
+ You have large areas of land you are cultivating.
+ To improve the production and health of fruit trees.
+ If you live in climates with heavy rainfall like the tropics.
+ If you live in a place with unique geology and calcareous rocks.
+ Land history of acid rain, industrial agriculture, or other forms of pollution.
The level of pH can be tested with at home kits or by professional laboratories. If you're concerned about the productivity of your soil, using The Carbon Garden 3-in-1 meter is a great way to get an understanding of your soil’s pH levels. Most issues arising with pH are due to soils with low pH. This can be remedied by the application of dolomite lime found in most garden centres.
Decorative Plants Optimum pH Ranges
| Plant | Optimum pH Range |
| Acacia (Wattle) | 6.0 - 7.0 |
| Agapanthus | 6.0 - 7.5 |
| Banksia | 5.5 - 6.5 |
| Bottlebrush (Callistemon) | 6.0 - 7.0 |
| Camellia | 5.5 - 6.5 |
| Eucalyptus (Gum Tree) | 6.0 - 7.0 |
| Grevillea | 5.5-6.5 |
| Kangaroo Paw (Anigozanthos) | 6.0-6.5 |
| Lavender | 6.5-7.5 |
| Lemon Myrtle (Backhousia citriodora) | 5.5-6.5 |
| Lilly Pilly (Syzygium) | 5.5-6.5 |
| Melaleuca (Tea Tree) | 6.0-7.0 |
| Oleander (Nerium oleander) | 6.0-7.5 |
| Protea | 5.5-6.5 |
| Rhododendron | 4.5-6.0 |
| Roses | 6.0-6.5 |
| Strelitzia (Bird of Paradise) | 6.0-7.5 |
| Viburnum | 5.5-7.0 |
| Westringia (Native Rosemary) | 6.0-7.0 |
| Wisteria | 6.0-7.0 |
| Xanthorrhoea (Grass Tree) | 6.0-6.5 |
| Yucca | 6.0-7.5 |
| Gardenia | 5.0-6.5 |
| Hibiscus | 6.0-7.5 |
Fruits Optimum pH Ranges
| Plant | Optimum pH Range |
| Apple | 6.0 - 7.0 |
| Apricot | 6.0 - 7.5 |
| Avocado | 6.0 - 6.5 |
| Banana | 5.5 - 6.5 |
| Blackberries | 6.0 - 6.5 |
| Blueberries | 4.5 - 5.5 |
| Cherries | 6.0 - 7.5 |
| Figs | 6.0 - 7.5 |
| Grapes | 6.0 - 6.5 |
| Kiwi | 5.5 - 7.0 |
| Lemon | 6.0 - 7.5 |
| Lime | 6.0 - 7.5 |
| Mango | 5.5 - 7.5 |
| Nectarine | 6.0 - 7.5 |
| Orange | 6.0 - 7.5 |
| Papaya | 6.0 - 6.5 |
| Peach | 6.0 - 7.5 |
| Pear | 6.0 - 7.0 |
| Plum | 6.0 - 7.5 |
| Raspberry | 6.0 - 6.5 |
Vegetables Optimum pH Ranges
| Plant | Optimum pH Range |
| Asparagus | 6.0 - 8.0 |
| Beans | 6.0 - 7.0 |
| Broccoli | 6.0 - 7.0 |
| Cabbage | 6.0 - 7.0 |
| Carrots | 5.5 - 7.0 |
| Cauliflower | 6.0 - 7.0 |
| Celery | 6.0 - 7.0 |
| Cucumber | 6.0 - 7.0 |
| Eggplant | 5.5 - 7.5 |
| Garlic | 5.5 - 7.0 |
| Kale | 6.0 - 7.5 |
| Lettuce | 6.0 - 7.0 |
| Onion | 6.0 - 7.0 |
| Peas | 6.0 - 7.5 |
| Peppers (Chilli/Capsicum) | 6.0 - 6.8 |
| Potato | 5.0 - 6.0 |
| Spinach | 6.0 - 7.0 |
| Squash | 6.0 - 7.0 |
| Tomato | 6.0 - 6.8 |
| Zucchini | 6.0 - 7.0 |
If you have any questions relating to plants and their optimum pH levels, don't forget to head over to the community and chat with one of our horticulturalists or one of the many experienced gardeners that reside there! Visit the Community Here