Plant growth will become far too luxuriant and sappy, resulting in weaker plants that are more susceptible to damage weather, diseases and insect pests. Young plants have a rapid intake of phosphorous, so it is important that seed beds and seed composts have a plentiful supply. Root crops such as carrots, potatoes, onions, parsnips, beets, etc. will all decrease in yield if there isn't enough available phosphate. Phosphate is also vital for the movement and storage of food reserves in plants, and is the main nutrient involved with the proper development of seeds and fruits. This gradually turns to a bronzy shade of green as the deficiency worsens.
Growth slows down and the plant gives a poor yield of fruit and seeds.
Generally, an excess of phosphate is not detrimental to most plants, as the root system closely regulates the uptake. Gardeners frequently use potassium or potash to improve the brightness of flowers as well helping cut flowers last longer. Potassium also helps toughen up plants, making them more resistant to pests and diseases. Potassium can also help, but not eliminate, problems caused by excess nitrogen. Potassium also plays an important part in the formation of sugars and starches.