QUESTION: What is the best fertilizer for leeks? Do I need to prepare the soil before planting? -Tim W.
ANSWER: Leeks should be fertilized regularly as well as planted in soil that’s been prepared and fertilized, and the best fertilizer to use is different in each instance. Before you plant your leeks, work plenty of rich, well-rotted compost into the soil where they will grow. If your soil has a pH level under 6.0, making it too acidic for the leeks, spread lime to correct the pH level and bring it into a range between 6.0 and 6.8. (If you don’t know the pH level of your soil and aren’t sure how to find out, read our article How to Test pH in Your Soil.) Apply a 10-20-10 fertilizer blend at half a cup for each 10-foot row (in other words, half a cup per 10 linear feet), and work the fertilizer down into the top four to six inches of soil.
Because leeks feed heavily on nitrogen, you’ll need to continue supplying them with fertilizer once they’re growing even though you’ve prepared the soil with fertilizer before planting them. About three weeks after planting the leeks, apply a liquid fish emulsion or other nitrogen-heavy fertilizer. Continue to feed the leeks with this fertilizer every three to four weeks for best results.
If the fertilizer you use is a dry granular variety, make sure to water it in well after sprinkling it on the soil. You can also use well rotted poultry manure sprinkled around the roots of the leeks to give them a boost of nitrogen.