To add potassium use a chemical fertilizer that has a high last number or an organic amendment like Greensand.
Vegetables also need a wide variety of trace minerals and nutrients to grow well. These include: Boron, Copper, Iron, Manganese, Calcium and Zinc all of which can be found in Essential Micro-Nutrient Granular Package.
Water is the most important thing for your garden and it required for proper cell structure, stability and growth.
Too little water will drastically reduce productivity and could kill the plant if withheld for prolonged periods.
Too much water is equally damaging and could result in leaf diseases or root rot.
Too wet an area attracts snails and slugs as well as causing needed nutrients leach out of the soil.
Irregular watering can stress your plants leading to low productivity or bolting.
When to Water
The best time to water your garden is in the early morning hours to provide the soil and roots time to absorb the water fully before the heavy afternoon evaporative processes begin.
Watering in the evening can lead to mildews, rusts and other diseases as the water sits over night on your plants.
Rule of Thumb - water thoroughly and deeply. A shallow watering drives the roots up instead of down resulting in a shallow root system leaves.
Tip - quality soil is an important consideration to the watering program.
Veggies grown in sandy soil the water will run out of the soil profile leaving the plants wanting water.
If growing in water-retaining clay the soil may become water logged causing other sorts of growth issues. Get that soil healthy with a generous amount of organic matter and mulch it thickly to conserve water in the garden.