Acid-Loving Plant Care

All plants react to soil pH, which is a measure of acidity or alkalinity on a scale between 0 and 14. The lower the number, the more acidic the soil; as you move up the scale the soil becomes more alkaline or "sweet." When the soil is partnered with a plant suited to its pH level, the plant will be able to accept the nutrients in the soil, allowing it to grow and be healthy.

Most plants grow best in a pH range close to neutral, with a slight touch of acidity, or 6.5 on the pH scale. Some plants, such as lavender and rosemary, prefer a sweeter soil, a pH above 7. Others prefer more acidic conditions, about 5.5; these plants are referred to as "acid-loving plants," as they require an acidic soil in order to take up the necessary nutrients that make them grow, bloom and produce fruit.

Popular acid-loving plants include rhododendrons, azaleas, blueberries, potatoes, strawberries and heathers. When planting and caring for acid-lovers it is important that their soil pH desires and acid-humus diet are met. There are several easy ways to accomplish this.

First, determine your soil's pH using a pH thermometer. A more elaborate way to test pH is at a soil lab, which is beneficial as the test also measures nutrient levels, and will quite often include handy tips to improve any deficiencies.

If the pH is higher than 6.5, it's time to acidify the soil. Pine needles, peat moss, bark mulch and leaf mould are all organic components that will lower pH. You can add these to the soil when preparing your garden beds, or use them once a year as a mulch to maintain soil acidity. Sulphur is another natural way to lower pH. To reduce the level by one full point, you'll need to add a little more than a kilogram of sulphur per 30 square metres (reduce this amount by one half if you have extremely sandy soil).

When watering is also the perfect time to maintain your acidic soil. Three times a year, water your plants with leaf mould tea, which will not only lower the pH, but also add potassium, promoting strong root growth, disease resistance and abundant flowering. Save your coffee grounds, which are rich in nutrients and tannic acid, and sprinkle them lightly under your shrubs to help keep the pH down. Another tip from the kitchen is to recycle leftover pickle juice (vinegar-based), mixing it with 20 parts water and pouring it over the soil. Or simply put all pickle juices, tea bags and coffee grounds into the compost - and be sure to use it often.

A common sign that plants are planted in too sweet a soil is when leaves or needles take on a yellow-green hue, a condition referred to as chlorotic. Plants become chlorotic when they cannot access nutrients (usually iron or manganese) due to the soil's high pH level. If a plant struggles too long, it may suffer from death of leaves, dieback of branches and lack of vigour. Left untreated for several seasons, the plant could die. To correct the problem simply lower the pH level and fertilize.

Acid-loving trees and shrubs often have shallow root systems. When planting, remember to dig a wide and deep hole, and amend heavy clay soils thoroughly. It is also important not to over-fertilize as the roots, being so close to the surface, will easily burn. To encourage long feet, water infrequently and deeply; the plant will reach farther through the cool soil to seek its water.

The perfect soil for acid-loving plants is an organically enriched, well-draining garden loam. If the soil becomes waterlogged and the plants sit with wet feet, they develop leaf scorch, resulting in wilted leaves with brown patches. Amend heavy soil with sand and organic matter, and if the problem is severe, planting in a raised bed could be helpful. Generally the soil in gardens planted near forest is naturally acidic from years of decaying forest debris. It is also common for these gardens to be invaded by weevils, as they appear to migrate from the forest into our gardens and are much attracted to acid-loving plants, particularly rhododendrons and primulas. An annual application of beneficial nematodes will help control their population.

Plants that prefer a lower pH will require similar care when it comes to feeding, mulching and pest control. When designing your garden, plan to keep the acid-lovers together in the garden bed, which will make their special care easier to provide.

Each spring begin your gardening with a simple pH test of your soil and plan your soil amendment around the results. Your rhodos, azaleas and camellias will thank you with bright-green leaves and huge, colourful blooms.

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