3 key tips for fertilizing your garden with potassium

Potassium is required for proper growth of fruits and flowers, ensuring good size, colour and number. Find out the best ways to provide the plants in your garden with this important nutrient.

Potassium, also called potash, is listed on fertilizer labels by its chemical symbol, K. It's the third essential nutrient, indicated last in the N-P-K fertilizer analysis.

• It helps plants build proteins and sugars, aids them in taking in other nutrients and helps them withstand cold weather and other types of environmental stress.
• Plants need potassium when the leaves turn grayish, yellow, mottled or brown and their edges curl; lower stems and leaves are often affected first.
• Symptoms usually occur late in the season, when potassium is in high demand by developing fruits.

• For a fast solution, spray plants with fish emulsion or liquid kelp.

Many gardeners use seaweed or kelp sprays monthly through the growing season to prevent possible potassium deficiencies. Potatoes and other root crops need abundant potassium.

Greensand and granite dust are good organic sources of potassium; both are slow acting and long lasting.

• Dig them into soil in fall so they'll be available when you plant in spring.
• One application often lasts for several years.

While organic fertilizers often supply secondary nutrients and trace elements, including calcium and zinc, their primary purpose is the same as that of synthetic fertilizers — to provide nitrogen, phosphorus and potassium.

• Select an all-purpose fertilizer that contains all three elements or use a single-nutrient type to correct a specific deficiency.

Granite dust

• Source: By-product of quarrying
• Content: 5 to 7%
• Application rate: 4.5 kg per 9 square metres

Greensand

• Source: Marine sediment
• Content: 3 to 5%
• Application rate: 4.5 kg per 9 square metres

Kelp meal

• Source: Processed seaweed
• Content: 12%
• Application rate: 450 g per 9 square metres

Liquid kelp

• Source: Extract of kelp meal
• Content: 12%
• Application rate: 30 ml per 4 L of water