If a plants leaves are yellow, then it is suffering from a condition known as chlorosis, which is a lack of chlorophyll. Chlorophyll is what gives a leaf its greenness, and is a fundamental componet photosynthesis, the mechanism which plants use to obtain energy from light. However the experienced gardener will be used to dealing with the issues of chlorotic leaves, will know what avoiding steps to take, and will be able to restore a sickly plant back to full verdant magnificence. These are some of the more typical causes of mellow yellow leaves.

Water. Too much or too little and you very quickly get yellow leaves. But with proper preparation of the ground before planting, drainage problems can be pretty much avoided. What you are looking for is adequate drainage, but with the ability to hold moisture like a sponge without getting water-logging, a particular problem if you have a clay soil, or draining too quickly as with sandy soils. Simply digging in organic matter before planting will promote a good soil pore structure, allowing excess water to drain off while retaining enough moisture for healthy plant growth. Manure is one option, a product such as Levington Organic Blend Farmyard Manure is a recommended commercial product. Purpose made soil conditioners are another way of achieving the same result, Miracle-Gro produce a wonderful Eco Sense Soil Conditioner, which is a peat free blend. Having dug in organic matter, don't forget to mulch to slow down evaporation and suppress weeds. There are plenty of options for mulching such as composts or barks like the Miracle-Gro Moisture Control Natural Pine Bark which helps retain moisture 6 times longer and stays functional for up to 3 years.

Creating a suitable pH balance in your soil is also important. As part of your soil preparation regime, you should find out whether your soil is alkali, acid, or neutral. This is called its pH. It's extremely important as it influences nutrient intake by roots, and can be found by using a commercially available test pack, easily obtainable from any horticultural centre. Having discovered the pH of your soil you might then realise that you're growing the wrong types of plants for the soil type, and this is causing the chlorosis, or it may be that you need to tweak the pH of your soil. For general gardening purposes, an optimum pH is about 6.5 which is slightly acidic. Should modification be required, then an organic mulch will help decrease alkalinity, while liming will bring down acidity. Also, working in organic matter will help to create a humus rich soil, which will have a high buffering capacity, that means a strong ability to resist change in pH. If you want to grow ericaceous plants (acid loving) but have the wrong soil type, perhaps switch to growing them in containers of Miracle-Gro azalea, camellia and rhododendron compost. Alternatively, if you want to grow these plants directly in your garden soil make sure you regularly feed them with an ericaceous plant food. Miracle-Gro have a choice of suitable liquid and granular feeds.

When the gloriously green leaves of a previously healthy plant start to yellow, nutrient deficiency is probably the main reason. And prime suspect is a lack of Nitrogen, which is crucial for plant growth. Once the vigorous growth of spring has slowed, the plant may have used up what nitrogen it could access. Deficiencies of iron, magnesium, sulphur, and molybdenum will also cause a yellowing of leaves. Fortunately, nutrient deficiency is easily avoided by a good feeding regime. In the spring, give established plants a suitable feed using a product such as Miracle-Gro Slow Release Plant Food. And treat your lawn with similar care, as without TLC, it will yellow too. A lawn feed and weed product like Evergreen Complete will provide the right nutrients at the same time as getting rid of mineral sapping weeds.