If a plants leaves are yellow, then it is most likely ailing from a condition called chlorosis, where the plant has insufficient chlorophyll. Chlorophyll is what gives a leaf its greenness, and is vital for photosynthesis, the process plants use to obtain energy from light. However the attentive, knowledgeable gardener will be used to dealing with the issues of chlorotic leaves, will know what avoiding steps to take, and will be able to return an unhealthy plant back to full verdant magnificence. Here are some common 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 thecapacity to hold moisture in the way a sponge does without getting water-logging, a particular problem if you have a clay soil, or draining too quickly as with sandy soils. Simply supplementing organic matter before planting will ensure a good soil pore structure, allowing excess water to drain off while retaining enough moisture for good plant growth. Manure is a great choice, a product such as Levington Organic Blend Farmyard Manure will most certainly do the job. Purpose made soil conditioners are another good option, Miracle-Gro produce a wonderful Eco Sense Soil Conditioner, which is a peat free blend. Once you have added organic matter, don't forget to mulch to reduce water evaporation and keep the weed down. 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 lasts for up to 3 years.

Poor soil through pH imbalance is another issue. As part of getting your soil ready for planting, 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 adjust the pH of your soil. For general gardening purposes, an optimum pH is about 6.5 which is slightly acidic. Should modification be needed, then an organic mulch will help decrease alkalinity, while liming will reduce acidity. Also, digging in organic matter will help to create a humus rich soil, which will have a high buffering capacity, in other words strong ability to resist change in pH. If you want to grow ericaceous plants (acid loving) but have the wrong soil type, try 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 toturn yellow, nutrient deficiency is the most likely cause. 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. Thankfully, nutrient deficiency is simple to fix using a good feeding regime. In the spring, provide established plants a suitable feed using a product such as Miracle-Gro Slow Release Plant Food. And don't forget your lawn, 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.