Potassium is great for the production of fruits, vegetables and flowering plants. However it must be present in sufficient but not overly abundant quantities at the right times in the plants life cycle.
Potassium facilitates the development of buds, flowers, and subsequently the fruits and vegetables that grow from them. Potassium also plays a key role in root development and is a constituent of plant cellular development. Potassium is needed for plants to metabolize other nutrients as well.
Towards the late phases of a plants life cycle it generally requires more potassium. The late cycle is when flowers and fruits are forming. When plants begin flowering adding potassium significantly increases yield and quality. In some instances maturity is expedited.
Potassium Deficiency Symptoms [potash deficiency]
1. Slower Growth Rate of both foliage, fruits and roots.
2. Susceptibility to disease, pests, temperature extremes and fluctuations. Increased potassium levels will decrease the intensity of many plant diseases.
3 . Browning and curling of leaf tips - leaf tip burn. Usually appears on lower leaves first.
4. Purple - purple-red spots sometimes appear on the leaf undersides.
5. Chlorosis - The most prominently isual symptom - leaves lack any luster, appear dull and frequently have a Deep green or blue-green tone along the veins. Differing slightly from the chlorosis that appears with other nutrient deficiencies..
6. Stems of certain plants, particularly solanaceous [Potatoes, Tomatoes, Peppers, Eggplants] are more woody than usual and at times hollow.
7. Die-back of shoots and new growth is common in brambles and small fruiting plants.
Excess Potassium - Potassium toxicity
Potassium is needed for plants to metabolize and take up other nutrients, but too much can also hamper other nutrients. Potassium and magnesium compete with each other for uptake, the potassium in over abundance usually wins.
If the plant is taking up too much potassium one of the first symptoms to appear will be a magnesium deficiency in the older leaves towards the plants bottom. The veins of lower leaves will retain their green color while the rest of the leaf will turn yellow.
Rectifying a magnesium deficiency is not overly difficult adding Cal-Mag generally does the trick. Magnesium Sulfate can also be used as a foliar spray.
Ideally potassium supplements are soluble and specifically formulated for hydroponic growing. Potassium Nitrate [KNO3] and Potassium Sulfate [K2SO4] and Potassium phosphate or Monopotassium phosphate [MKP] are the most commonly used. Potassium silicate is at times used in some crops when they are grown for their essential oils - such as herbs and wacky weed.
These nutrients generally come in soluble crystalline powder, but can also be an in solution formula which can be diluted and used as a foliar spray.
Boosting Harvest - Potassium Supplements
If your plants seem to be stalled in their growth particularly durring the flowering and fruiting phase there's a good chance your potassium is depleted. Look for other symptoms described further up in this article but in the interim boosting with a potassium supplement will in all likelihood be advantageous. The worse case scenario is that you create a magnesium deficiency which is easily rectified.