Garlic enjoys a good spring feeding when plant foliage is about 3 inches tall. Some areas of the country will be ready to apply fertilizer in March, while other areas with colder growing climates may need to wait until April.
Tip #1 — Choose What's Right for Your Garlic and Garden
There are several organic fertilizers you can use, including liquid sea kelp, powdered kelp, fish meal, or blood meal.
While there is some debate about which option is best, powdered kelp is a good, cold-hardy fertilizer that does well in early spring when hard frosts are still likely.
Foliar sprays work best if applied a day or two after an irrigation or rainfall. If you'd rather apply fertilizers to the soil, you can do a side dressing along the rows or broadcast across the bed. Dried blood meal is a great organic source of nitrogen that becomes available slowly over 1–6 weeks as it decomposes naturally in the soil.
Tip #2 — How Often Should You Feed Your Garlic?
You can apply a foliar feeding every two weeks from about mid-March to early May, with a total of 3–4 applications. Once the leaves quit growing, stop applying any foliar nutrients (mid to late May). At this point, due to mounting heat, additional applications could cause the leaves to yellow, and the plant can no longer utilize the nutrients.
Regardless of the fertilizer you choose, it should be applied in early to mid-spring, avoided during late spring, and never applied to water-stressed plants.
Tip #3 — Apply the Right Amount
Make sure to read and apply fertilizer according to the directions on the package.
Tip #4 — Do NOT Feed Garlic in Late Spring
Garlic leaves stop growing in late spring. At this time, the plant's energy begins to move toward bulb development. Adding high nitrogen in late spring can actually delay the bulbing process and result in reduced garlic size and yield at harvest.
Tip #5 — Dry or Yellow Tips
Many gardeners notice yellow or brown on the tips of leaves, but not the rest of the leaf. This is most likely frost or wind damage from when the foliage was first sprouting — and is normal for most garlic across the country. These dried tips will not affect bulb development, nor does it mean you need added nutrients.
Yellowing of the entire leaf in April or May, however, could be an indication of water or nutrient deficiency.
Garlic Gods refers to, and sources information in this article from the book "Growing Great Garlic" by Ron L. Engeland.