Fuchsias, like all plants, require light, air (carbon dioxide) and water to produce sugars by photosynthesis. These sugars, together with water and dissolved nutrients absorbed from the soil, are used to make up the building blocks of the plant.
In nature the root system searches for water and nutrients. Potted plants are dependent on being fed and watered regularly.
Fertilisers are either of organic origin, that is, derived from once-living plants and animals, or inorganic and chemically synthesised. Organic fertilisers in the soil are released slowly over months, by bacterial and fungal action. Soluble inorganic fertilisers are usually given weekly; they are available immediately but are leached out with watering.
The major nutrients (macronutrients) NPK needed for optimal plant growth are Nitrogen (N), Phosphorus (P) and Potassium (K for Kalium). Essential micronutrients (trace elements) such as Magnesium (Mg), Calcium (Ca), Iron (Fe) and Boron (BO), Manganese (Mn), Zinc (Zn), Molybdenum (Mo) and Copper (Cu) are required in much smaller quantities, and are sufficiently present in growing mixtures.
Nitrogen is needed for green bulk growth like stems and leaves. Phosphorus is necessary to develop a strong root system and to promote good general health, while Potassium hardens the branches to carry the flower load and deepens the colour of blooms.
The relative proportions of nitrogen and potassium required change with the season. In spring, rapid green growth requires more nitrogen, whereas in the flowering stage, from early summer onwards, more potassium is required. In the dormant winter stage, after pruning and re-potting, minimal feeding is needed.
Newly potted-uprooted cuttings and plants do not require feeding for the first few weeks as the usual growing mixture of compost, kraal manure, potting soil and vermiculite/perlite (2:1:1:1 parts) will contain sufficient nutrients.
By law, the proportions of NPK in inorganic (synthetic) fertilisers have to be given on the container e.g NPK 3:2:1 is a high nitrogen feed, whereas NPK 3:1:6 contains more potassium. Balanced fertilisers NPK 1:1:1 are not in much use during the long growing season in South Africa.
Fertilisers such as Multifeed Classic NPK 19:8:16 (43), Multifeed Flowergro NPK 3:1:6 (46) also contain the essential micronutrients, as do most other general use fertilisers. The figure in brackets is the percentage by weight available as plant food: >40% is quite high and has more risk of burning the roots if overdosed. Fuchsias are not too fussy about which fertiliser is used, as long as the seasonal requirements are kept in mind.
Nitrosol (NPK 8:2:5.8) is a high N liquid organic plant food made from animal residues and is immediately available like the above. It also contains a growth stimulant gibberellic acid and is very easy and safe to use.
Methods of feeding
Foliar Spray: Cuttings are initially rooted in nutrient-free media such as seedling mixture, palm peat, or perlite and vermiculite to encourage a good root system in the search for nutrients. It is advisable though to foliar-spray rooting cuttings with a dilute fish emulsion (Seagro) and Kelpak, a seaweed growth hormone, once or twice during the 4-6 weeks rooting period. This is also useful for small plants that do not as yet have a good root system. Sprays of any description tend to stain buds and blooms and are not used once flowering starts.
Watered in: This is the usual method: it is best to water the plant the night before and then give the dissolved fertiliser the next morning – never fertilise a dry plant. Fuchsia are heavy feeders and are fertilised every 7-10 days, or more often in an appropriately diluted form with every watering.
At all times it is most important to follow the instructions on the container. Too concentrated a solution makes it difficult for the plant to absorb water and dissolved nutrients against an osmotic gradient.
Nurseries fertigate daily i.e. the fertiliser is added to the irrigation water and they often use soilless growing media that may or may not contain a slow release fertiliser. It is advisable to repot such plants into your own growing mixture or plant them out into the garden soon after they have been bought.
Organic & Slow Release Fertilisers
The nutrients in organic fertilisers such as bone meal (P and Ca), hoof and horn (N), blood meal (N, K), worm casts and home-made compost are released slowly and are safer to use, but are less predictable in their effects and never solely relied on. Experienced growers often mix one or more into their growing mixture before use.
Bounce Back and Seamungus (with added seaweed, fishmeal, humic acid) are mostly chicken manure in pellet form and may be incorporated in the growing mixture or sprinkled, like other organic fertilisers, on the compost surface once or twice a season: a little is dissolved with every watering.
In synthetic slow release fertilisers like Osmocote, the granules have a semi-permeable resin coating which, once watered, releases the fertiliser gradually over specific periods of 3, 6 and 9 months. They are mixed into the growing medium, and the rate of release increases with the soil temperature. They are especially useful in baskets. The Osmocote NPK ratios are approximately 3:1:2.
Overfeeding with nitrogen (N) results in lanky lush plants with dark green leaves, but few flowers, whereas an excess of potassium (K) produces smaller, woodier plants with colourful flowers. One dose of potassium sulphate (5gm in 5 litre water) at the budding stage is acceptable in order to improve the colour of the flowers.
Nutrient deficiencies in general will result in stunting, and the plant does not look healthy, but there are few specific signs. Leaves that turn yellowish with the veins retaining their normal colour may be indicative of magnesium or iron deficiency, but this may also be due to old age or the plant has not received enough light inside the foliage. Epsom salts (MgSO4) one tablespoonful/5 litres water given once or twice a season and Iron chelate (Fe 5gm/10 litre water) once per season may be given to prevent this, especially if plants have been in the same pot for more than one year.