Agapanthus 'Back in Black' will put in a good performance both in the border or  as a potted patio plant. However, a little extra care is necessary to enjoy it year after year in cooler regions.

Hardiness
A semi-hardy deciduous variety, 'Back in Black' can survive unprotected to 40°F (+5°C). For temperatures down to 23°F (-5°C), plants can remain planted in the border if covered with 2-4" (5-10cm) of  leaves or straw, which can be kept in place with some sand.  This will also protect from dry frost, which is very harmful to the plants.

If temperatures are likely to fall below 23°F (-5°C), the solution is to overwinter it indoors. If you are going to do this the best way is to grow the plants in pots. These may be decorative outdoor containers, or you might want to consider sinking a plain pot into the border for easy removal for winter. For details see below "Growing in Pots".

Positioning
Agapanthus prefers a position with lots of sun and little or no shade. Soil should be rich in humus with good drainage. It is important that the soil is kept moist during spring and summer.

Growing in pots

Select a size of pot large enough for the plant to grow in for up to 3 years. This would probably be 3 gallon / 7.5 litre. It's a common myth that growing Agapanthus in a small pot helps to stimulate flower production - this isn't true! Re-plant every 3 years in a larger pot, or divide the plant.  This can be done in spring, when they have started to grow, or after flowering.

The best soil is a mix of humus rich soil with 20% clay (to retain moisture) and some sand or grit for drainage. Organic or other basic fertilizer can be mixed in the soil. A layer of sand or bark can be used to help to prevent evaporation.

Plants in pots can be brought inside for the winter, but not too early, as they need to feel some cold in order to bring on winter dormancy. The plants need to be stored somewhere cool, preferably 32°F to 50°F (0°C  to10°C), in order to produce flowers for the following season. As ‘Back in Black’ loses its foliage in winter, it doesn't matter if the storage area has sunlight or not.

The pots can be brought outside again from early April, but still need to be protected from severe night frosts.  However, don't bring the plants outside too late as that might cause the leaves and stems to be pale and weak.

Water and fertilizer

It is important to keep the soil moist during growing season, so daily watering will be probably be necessary on warmer days for container-grown plants. After flowering, watering should gradually be reduced, and during winter the plants can be kept rather dry, so watering is not needed then.

Plants should be given fertilizer in spring, and again in August, during flowering. The fertilizer used in August should contain a high potassium content in order to build the plant's strength up before winter.

You can leave the spent flowers on the plants, as the black seed heads are very ornamental. They also look great in dried flower bouquets.

Early in the season slugs can eat some of the young leaves, but this is not a serious problem and the plant will easy grow over it.
Viruses can occur in Agapanthus, but usually cause no harm to the plants.