How to Improve Shop-Bought Potting Soil

To grow well, the roots of your plants need:

Air
Moisture
Nutrients

Air - In general, most potting mixes sold commercially around here have good aeration. You can tell by how light and crumbly the mix is. If you are using a container with potting mix from last year, it may have compacted a bit. It's a good idea to fluff it up with a fork and combine with some new mix to ensure your roots don't suffocate once they reach the lower half of the pot.

Moisture- Your potting mix must drain water well but also retain moisture efficiently. Most especially in the growing season here that sees little rain and a lot of sun, watering needs of plants can be huge and quite demanding. At times, potting mixes dry up very quickly despite regular watering and stress your growing plants. I like to add some Perlite, a naturally occurring volcanic glass with several excellent characteristics. It is sterile, lightweight, odourless and retains moisture and nutrients within your growing medium while improving aeration.  It also reduces extreme soil temperature fluctuations. So in order to keep those pots light and to make your water last longer, add a few handfuls of perlite to your container along with potting soil and fertiliser. You can find perlite in Warsan nurseries in Dubai.

Nutrients/ Fertiliser

NPK is no longer the mystery to me that it used to be. It's really quite simple, even if you have the most vague memories of the periodic table.

N- Nitrogen, P-Phosphorous and K-Potassium stands for the three major elements needed for plant growth. Plants also need micronutrients such as iron and magnesium.

This is how the nutrients work:

N for leafy growth
P for root growth
K for flower and fruit set

Compost - Compost is an excellent soil conditioner and fertiliser. It creates organic reserves within the potting medium that release nutrients slowly over time. You can therefore add as much compost as you want to your container without running the risk of 'burning your plants'. Humic substances in compost help nutrients become more readily available to your plants. However, quantities of phosphorous, nitrogen, potassium, sulphur, calcium and other micronutrients present in your compost can vary from batch to batch. In some cases, plants may need an additional dose of fertiliser to grow well. You can use any of the fertilisers detailed below in combination with compost to ensure healthy growth and a good harvest from your vegetable plants.

Commercially, there's very few 'compost' brands available in the UAE. However, most potting mixes available are actually compost-based containing more than 50% organic matter.  So you may not know it but you are already starting out with some compost. You can also make your own compost at home using the Bokashi system.

Cow manure- Using manure is another way to add valuable organic matter and fertiliser to your soil. Locally, I have seen heat-treated cow manure sold in plant nurseries in Warsan. Fresh manure must be treated and aged before it can be used in the vegetable garden. Cow manure is not as rich in nutrients as say, chicken manure, but that makes it safe to use in large quantities. It has a high ratio of nitrogen which is great for giving young plants a good start. You may however have reservations about using manure if you want to use purely vegetarian or strictly organic growing methods. There are alternatives such as Alfalfa meal, Seaweed and Kelp. Shalimar Herbals has recently introduced a Cocopeat fertiliser that includes seaweed. However, I have not personally tried it yet.

Bone meal - Bone meal is a mixture of crushed and ground animal bones, often used in organic gardens. It is a great source of phosphorous and is commonly added to planting holes before putting in transplants as it encourages strong and healthy root growth. However, used on its own, it is not a sufficient source of nitrogen and potassium. Bone meal is hard to come by locally but you may just chance upon it in a plant shop or garden centre.

Fish Blood and Bone- Fish Blood and Bone is an excellent multi-purpose fertiliser with just the right balance of nitrogen, phosphorus and potassium for your vegetable plants. I recently came across organic fish-based fertiliser pellets in Satwa and Dubai Garden Centre (Dhs 15-19).

Neem fertlizer-  Neem-based fertilisers are a great vegetarian source of nutrients for your plants. Locally, I have only found Shalimar to sell a Neem Herbal fertiliser which has a high ratio of nitrogen along with other nutrients and of course, Neem's incredible capability to repel pests such as nematodes.

NPK - 'NPK' is usually used to refer to synthetic fertilisers with very specific quantities of nitrogen, phosphorous and potassium alongwith trace elements such as magnesium and iron. Most vegetable plants need a fertiliser high in potassium, which aids flowering and fruiting. Be careful to read the label on any fertiliser you buy, organic or synthetic. Products such as GrowFast or Phostrogen can be added to the potting mix in recommended quantities to fertilise your plants. They don't do anything in the way of improving soil structure and introducing healthy microbes.

Different plants have different nutrient needs

Leafy vegetables such as spinach, lettuce and herbs will appreciate an all-purpose fertiliser or one high in Nitrogen for good green growth.

Fruiting plants such as tomatoes, aubergines and beans benefit from a high potassium fertiliser, especially one they begin to flower.

Root vegetable plants such as potatoes need to be fertilised with fertilisers high in both phosphorus and potassium.

Some vegetables such as carrots and radishes are actually not too bothered about being fertilised. Indeed, they don't much like it. If grown in soil too rich, they will produce abundant leafy growth but misshapen, woody roots.

Do leave your comments and experiences with fertilisers below. I look forward to hearing from you!