Get the garden fit for spring: Healthy eating for plants

By Andy McIndoe

Health and fitness is high on the agenda: exercise, healthy eating, weight loss, stress reduction. These subjects are even higher profile during the first few weeks of every New Year when many are determined to make changes for the better in their lifestyle. Sometimes its maintained, and sometimes those good intentions.......well let’s just say the good intentions were good!

Rose flower power

It’s often the same in the garden. Its spring and we head off to the garden centre and stock up with lawn food, vegetable fertiliser, tomato food, something for the roses and a few bags of smelly stuff to sprinkle around, just to let the neighbours know we are out there gardening. By the end of the season some are still in the shed; maybe that regime has not been adhered to as intended.


With this in mind I thought it would be worth reminding ourselves about the basics of plant nutrition and its importance. To get the best from your plants healthy eating is just as important as it is for you.

I should say that most plants will grow on most soils, and that most soils contain adequate nutrients to support plant life. However in a lot of cases this is a bread and water regime, rather than the nutritious and balanced diet of an athlete.

Rhododendron Colonel Coen' single

Just remember that healthy eating is essential for growth and development in the early stages of life, also to maintain health when we reach maturity. Sometimes we need to eat more when we need an extra boost, when our level of activity accelerates. That’s how I like to think of the plants in my garden, as the season gets under way. They all have their challenges ahead: growth, fruit, flowers and the need to resist pests and disease. I want them to perform at their peak, so I think about what they need in the way of food.

The self-sufficiency of plants

Unlike animals plants have the ability to manufacture their own food. Remember photosynthesis? - The process that goes on in leaves and stems, making food from carbon dioxide and water in the presence of sunlight. Well that’s the basic diet, but what about extra requirements?

In the wild plants choose where they grow. They thrive where the soil is right for them and they struggle, and may fail where it isn’t. The garden is different; an artificial environment. We choose what we plant, and where. If your garden is anything like mine there are far too many plants crammed in close together, all competing for available food and water. Therefore I need to provide more of both essentials.

The three main plant nutrients

There are three main plant nutrients; I think of these as the carbohydrate, fat and protein of a plant’s diet. Each is essential for the development of a certain part of a plant.

Nitrogen is responsible for leaf and stem growth. It is vital to nearly all plants in the early stages of growth. It is essential to leaf crops, for example lettuce, cabbage and spinach. The lawn needs plenty of nitrogen when it starts to grow in spring, but beware, overdoing it may mean you are out there with the mower every couple of days for the rest of the year.

Phosphorus, usuallyreferredto as phosphate, is responsible for root growth. As all garden plants are dependent on their roots and this is essential in plant establishment. ‘Bone Meal’ is a traditional source of phosphate used at the time of planting in the UK, although other slow-release, more complete fertilisers have superseded it.

Potassium, usually known as potash,is responsible for flower and fruit production. Potash is very soluble so is easily washed away, it needs regular replenishment for crops that need it. Tomatoes and peppers need plenty of potash to fruit well. Roses need potash to bloom; additional potash in midsummer guarantees a bold autumn encore.

How do I know what’s in a fertiliser?

Packaging usually tells us the proportion of each of the plant nutrients that a fertiliser contains. In the UK this is expressed in letters and numbers (indicating the percentage of each main nutrient) always in the same order: Nitrogen (N), Phosphate (P), Potassium (K). For example the nutrient content of “Growmore” is 7:7:7, equal percentages of each nutrient. Growmore is a chemical fertiliser. It is a fast release product, useful for a boost on the veg. plot, but there are better options such as organic Fish Blood and Bone.

Organic or inorganic?


Organic means a fertilisers derived from something that was once living, in other words plant or animal remains. Naturally occurring minerals, although not organic are usually also acceptable in organic food production. Chemical fertilisers are man made and usually contain higher nutrient levels and these are quickly released into moist soil.

Organic fertilisers usually contain lower concentrations of plant nutrients, but these are released slowly into the soil over a long period as the organic material breaks down. This means there is less risk of overfeeding delicate plants.

The consequences of overfeeding

When we apply a fertiliser it dissolves in the water that surrounds the soil particles next to the plant’s roots. Plant roots are delicate structures. The root hairs are the active parts: single cells where water and nutrients pass from the soil into the plant. If the solution of nutrients in the soil water is too strong water may be drawn out of the plant into the soil’s nutrient solution rather than passing into the plant. The results: the plant wilts and the root hairs may be permanently damaged. This is a more common problem when quick release chemical fertilisers are used excessively.

To avoid overfeeding never feed when the soil is dry, use an organic feed, a dilute liquid fertiliser or a controlled release fertiliser.


The other elements of a healthy dietVitamins and minerals of the plant world

In addition to the 3 main nutrients there are others needed in both large and small amounts. Plant requirements vary and to make matters more difficult there is a complex relationship between soil pH and the availability of certain nutrients to certain plants. The best example of this is iron which is unavailable to ericaceous plants on an alkaline soil: this results in a deficiency, and the plant struggles to grow.

Fertiliser formulations

Liquid: a concentrated liquid fertiliser is diluted in water and applied to soil or compost in the growing season. It is fast-acting and used regularly to provide the nutrients the plant needs. For example liquid tomato fertiliser.

Soluble: a powder or crystalline solid that is dissolved in water and used as a liquid fertiliser. It is fast acting and either general or specific to a certain crop.

Granular: Solid fertilisers made into easy to handle granules. They can be slow or fast release and most are general fertilisers supplying the main, and sometimes minor, plant nutrients.

Slow release solid: Fertilisers that gradually break down in the soil releasing nutrients over a long period. Organic based fertilisers fall into his category, for example Fish, Blood and Bone, widely available in the UK.

Controlled Release: Fertilisers in specially coated granules that only release nutrients into the soil when there is sufficient moisture, and the temperature is warm enough; ideal in pots and hanging baskets.

Choosing a fertiliser

A slow-release fertiliser supplying balanced quantities of the main nutrients and trace elements is the best choice for general use. You can supplement this with fertilisers that have a higher content of a specific nutrient for certain crops. For example use tomato fertiliser for tomatoes: this has lots of Potash for fruit production.

Soil types and plant nutrition

As I said at the beginning most soil contains sufficient nutrients to support plant growth. Soils with fine particles, such as clay, are usually the most fertile. They hang on to nutrients in the soil water, keeping them available for the plants. Soils with larger particles, such as sand are free draining and lose nutrients more quickly; therefore the plants growing on them probably need more feeding. This is true also true in containers: we water pots regularly so nutrients need replenishing as they are washed away.

37. Backfill with compost and soilI hope this answers a few of your questions about feeding, but it’s a big subject. Do post your questions and comments below – I will be happy to answer them. Also let’s have your secrets of a healthy lifestyle for plants wherever you are in the world. Once we get the diet right maybe I’ll move on to the benefits of gardening as a form of exercise. Hope your back isn’t aching yet................

Andy McIndoe

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