It is important to ensure that your plants have food in order to grow.
Insufficient nutrients in the soil can lead to all sorts of issues from tiny vegetables to blossom rot.
Signs of nutrient deficiency are as follows:
•Light or yellowed leaves
•Purple or red colored spots
•Leaves that are curling, brittle, or dry
•new leaves dropping off
•growing point (Terminal bud) dies
•Prominent showing of the leaves veins
•Fruit develops rot at the blossom end
I am certainly not an expert in the area of soil management but basic science tells me that if you are growing in a pot or container the plant will eventually drain the soil of nutrition.
Most commonly the deficiencies in your garden will be one of the following:
Nitrogen – This is one of the most familiar deficiencies causing yellowing and making the plant weak and spindly.
Give plants. Compost enriched with manures, tea and coffee grounds, soy bean meal, feathers, garden wastes, and kitchen wastes makes an excellent long-term source of nitrogen.
Too much nitrogen is as bad as too little. The most obvious signs of excessive nitrogen include plants with weak and has stems that break easily during windy conditions. Aphid infestation is another symptom. Studies show that these pesky insects prefer to feed on plants that receive excessive nitrogen
Nitrogen is abundant in the world, but most of the nitrogen in the world is a gas and most plant cannot use nitrogen as a gas. Most plants must rely on the addition of nitrogen to the soil in order to be able to use it. There are a few plants that love nitrogen gas, though. They are able to draw the nitrogen gas from the air and store it in their roots. These are called nitrogen fixing plants.
Nitrogen fixing plants do not pull nitrogen from the air with the help of a bacteria called Rhizobium. The bacteria infect plants such as peas and beans and use the plant to help it draw nitrogen from the air. The bacteria convert this nitrogen gas and then store it in the roots of the plant.
When the plant stores the nitrogen in the roots, it produces a lump on the root called a nitrogen nodule. This is harmless to the plant but very beneficial to your garden. As the plant dies, decomposition release the stored nitrogen into the soil, making it available for other plants.
In this way you can use crop rotation, placing broccoli and cabbage in a spot where bean and peas have grown the year before. Or you can use them as a companion plant such as the 3 sisters from Incas where beans, corn, and pumpkins are grown together.
Below are a few text book pictures to explain the science stuff
Phosphorus – is needed for photosynthesis, plant maturity, healthy roots it should also be supplied to the compost pile. Good sources are wood ashes, citrus wastes, egg shells, chicken manure, and some animal products such as fish bones (if you wish to use these).
Potassium - increases photosynthesis by increasing the amount of chlorophyll in leaves. That results in plants that better utilize available light. Excellent natural sources of potash for a summer quick fix include liquid seaweed, well-rotted cow manure, chicken manure or banana tea (see below).
Bananas are packed with nutrients, and that includes their peels. To make it, fill a large jar with water, and add a sliced banana peel. Let it sit for 48 hours.
Water your plants as usual with your banana tea.
Dried banana peels are :
42 % potassium
3.25 % phosphorus
Banana peels do not contain nitrogen but do contain Calcium
Calcium, Magnesium, & Sulfur - are often thought of as secondary elements.
Your tomato plant's upper leaves yellow from a calcium deficiency. That symptom differs from a lack of nitrogen, which causes yellowing of lower leaves. Stems of tomato plants that lack calcium feel soft to the touch, and fruits exhibit blossom-end rot.
Artificial fertilizers are not sustainable so I would strongly encourage you to use natural fertilizers such as self-made compost. As I live in the city I usually use store bought organic liquid fertilizer and I use Epsom salt to add magnesium sulfate, egg shells for calcium, and banana peel tea for potassium.
There are too many potential problems to list but most of these things can be found online. If you cannot find the answer please feel free to email me and I can try to help.