To bloom regularly, fertilize agapanthus twice a year, either after blooming, in early fall (September in the Upstate, October in the Lowcountry), or in early spring (early March in the Lowcountry and April Upstate). A low-nitrogen, complete fertilizer that includes phosphorus is best, such as 5-10-15 or 8-8-8.
Fertilizer. Since agapanthus plants are frequent bloomers, it's a good idea to fertilize them twice a year—in early spring and again two months later. Give them a balanced granular fertilizer such as 10-10-10 or one slightly higher in phosphorus than nitrogen to keep the blooms going all season long.
Give agapanthus lots of sun, plus extra water when its really hot and dry and they'll bloom abundantly. Agapanthus plants that fail to flower are usually growing in too much shade.
If you want the best success with fertilizing your agapanthus then use several different kinds. Rotate these fertilizers throughout the year for the best success. If you would like to use alternatives to commercial fertilizer then purchase Kelp Meal, Alfalfa Meal, or Epsom Salt.
Insect-eating plants such as Pitcher plants, sundews and Venus flytraps are other plants that do not like Epsom salt. They've adapted to growing in poor soils and even a little can kill them.
Agapanthus thrive in full sun and need 6-8 hours of sunlight each day. However, they do better in partial shade in hot climate areas. Agapanthus perform best in fertile, moist and well-drained soil. They show no preference for pH, except Agapanthus africanus which prefers an acid soil.
Without deadheading, the plant goes to seed and the blooming season is shortened considerably. To deadhead agapanthus, simply use pruners or garden shears to remove the faded flower and the stalk at the base of the plant.
Anthracnose
Overwatering and too much moisture on the leaves can contribute to this infection. Symptoms include brown spots on the leaves that can sometimes have purple edges. In the case of a severe infection, the spots turn black as the tissue dies and foliage can turn yellow, eventually dropping from the plants.
While the agapanthus is a low-maintenance plant, you will need to follow a few tips on agapanthus care to get the most out of your blooms. Mulch your agapanthus plants in autumn and feed twice during the growing season from early spring onwards. Water your agapanthus plants regularly.
Light pruning at strategic times of the year can keep your agapanthus healthy and in bloom over the summer. Cutting back the spent foliage in early spring allows room for new growth to emerge and maintains a tidy appearance.
Feeding. Feed border agapanthus flowers in spring with a balanced fertiliser, such as Vitax Q4, Growmore or fish, blood and bone. For agapanthus in containers, use a liquid fertiliser – such as Phostrogen or seaweed feed – and feed fortnightly until the flowers begin to show colour.
Potash-rich fertilizers include tomato fertilizer (either in liquid concentrate or granular form) such as Vitax liquid tomato feed or fertilizer for flowering plants such as Vitafeed Flower and Fruit Soluble Feed (Thompson & Morgan) 'Straight' or potash-only fertilizer comes in powder form.
Sun: Full sun or partial shade. Water: Drought tolerate however will benefit from regular watering. Soil: Well drained soil. Improve soil with soil conditioner or cow manure when planting.
Dividing and transplanting agapanthus
However, if left untouched for any length of time, they will become overcrowded and may flower poorly. Lifting and dividing agapanthus every 3 to 4 years will promote better flowering.
It is a perennial plant that can live for up to 75 years. Its evergreen leaves are 2 cm wide and 50 cm long. Its inflorescence is an umbel. The flowers are blue, purple or white and bloom from late spring to summer, followed by capsules filled with black seeds.
“Agapanthus stems can be pruned at ground level when the flower has gone over unless you want to leave them in the garden for winter structure,” says Patrick Fairweather, the Managing Director of Fairweather's Nursery.
The Agapanthus plant leaves will turn yellow when put under direct light of very high intensity. Provide some shade for them during the afternoon hours at least. Overwatering will also turn the leaves of this plant yellow, soggy and plump.
Agapanthus are best planted in a moist but well-drained soil of sand, clay, chalk or loam within an acidic, alkaline or neutral PH balance. They are best positioned in full sun. As they prefer their roots to be restricted, they make great pot plants.
Verdict: Unless you have a magnesium deficiency in your garden, there is no need to add Epsom salts. Doing so could even be harmful to soil, plants and water. Find out more about healthy soil and getting a soil test.
In gardening, Epsom salt can work as a plant fertilizer for garden plants and houseplants and can reverse a magnesium deficiency in the soil.