Early Potassium Tips for Healthy Tomatoes and Peppers

By Blake Jackson

Early-season potassium management is crucial for producing high-quality tomatoes and peppers while minimizing packing house losses. Often, the first fruit show yellow shoulders, a sign that potassium demand starts about two weeks before the first flowers appear.

Applying extra potassium early sometimes referred to as “banking” potassium can help maintain adequate levels for the initial fruit set.

Before increasing potassium, ensure your irrigation or fertigation solution is at the proper pH. Tomatoes and peppers absorb nutrients most efficiently at a pH of 6.2-6.5. For growers using water from limestone aquifers, this may require constant acidification to reduce pH.

Test water in a laboratory for pH and alkalinity in ppm bicarbonate. Because pH is logarithmic, even small deviations from the ideal range can cause significant nutrient deficiencies.

Common acids used include sulfuric or citric acid, with citric acid suitable for organic operations. Use an online alkalinity calculator for accurate dosing and follow instructions carefully.

Tissue testing should begin once plants are large enough to provide full-sized mature leaves without harming growth. Shift to a higher potassium fertilizer roughly two weeks earlier than usual and start weekly foliar potassium applications, ensuring the fertilizer is foliar-compatible.

Maintaining tissue potassium levels above 3% from flowering to harvest maximizes flavor and prevents yellow shoulders or gray wall.

Other key nutrient targets include tissue nitrogen around 4% during fruit development to avoid soft fruit and excessive foliage. Calcium should be near 3% and magnesium between 0.8-1% to prevent cracking and ensure durable fruit for shipping. While bi-weekly tissue testing was previously recommended, weekly sampling is now preferred for more precise management.

If you have incorporated 30-50% of your soil test-recommended potassium, calcium, and magnesium during soil preparation, maintaining these levels throughout the growing season can increase yields and reduce post-harvest losses.

Careful nutrient management, particularly early potassium application, supports consistent, high-quality tomato and pepper production while enhancing marketable fruit.

Photo Credit: gettyimages-bastetamn