Gardenia shrubs require nitrogen-rich fertilizers that help to maintain an acid soil with an approximate pH of 5.5. Cottonseed meal, blood meal and fish emulsion are good choices. Gardeners need to apply enough fertilizer to supply approximately 1 pound of nitrogen per 1,000 square feet of garden space.
Gardenia gardeners should apply fertilizer to shrubs a minimum of twice annually. They should make the first application at the first sign of new growth after the dormant season and the second during the height of the growing season. Some gardeners choose to fertilize monthly from the appearance of new growth to about one month before the first killing frost.
When applying fertilizer to these shrubs, gardeners should keep it at least 6 inches from the plant stems, as it can burn them. Broadcasting the product over the area where the roots grow provides the best method of application. Once the fertilizer is in place, it requires watering so that the plants can absorb it.
Container grown gardenias also require regular feeding. Owners need to select fertilizers the manufacturer formulates for acid-loving potted plants. Because the chance of damaging a container-grown plant is higher and the directions for use vary by product, it is essential for owners to read and follow the label directions for the product they select.