Watering Fuchsias in Pots or Baskets
The optimum temperatures for growing fuchsias are 20-250C during day and 18-200C at night, but these are often exceeded in summer – correct watering is crucial for good results.
Plants lose 97-99% of the water, absorbed via the roots, by evaporation through stomata (pores) on the undersides of their leaves, and the rest from the soil surface and the permeable sides of coir baskets and clay pots. When this loss exceeds uptake by the roots the plant loses turgor and wilts.
Soils fulfil several functions – anchorage for the roots, nutrient retention, aeration as roots need air/oxygen for normal root function, and water retention to sustain plants between waterings. Roots are the heart of the plant and a balance between water retention and adequate drainage, thus aeration is absolutely essential: as water drains from soil air takes its place and vice versa.
Two forces cause water to move through the soil – gravity and capillary action: that latter is a function of the natural forces of adhesion and cohesion. Adhesion is the tendency of water to stick to solid objects like soil particles and the sides of the pot, forming a thin film. Cohesion is the tendency of water to stick to itself - leading to droplet formation. Aeration and drainage are inversely linked to particle size; the smaller the particles, the greater the total surface area and thus water retention, and thus the composition of the soil mix is all important. The soil components also need to retain their structure for extended periods of time to avoid compaction, which leads to poor drainage.
Containers have a natural water table – water is retained in a layer of soil at the bottom and does not drain out, as the capillary pull of the soil particles equals the pull of gravity. This layer remains saturated. Watering or rain will temporarily raise the water table or it can evaporate or be used by the plant, but physical forces will not allow it to drain further. The smaller the soil particles (heavy clay soil), the higher this water table will be and the less the aeration.
Practical point: A drainage layer of pottery shards in the bottom does NOT improve drainage: the perched water table will just be higher in the pot (and less soil is available for use by the roots) – since this depends on the balances between gravity and the capillary actions in the soil and not on the drainage layer.
If five containers of different heights and diameters are filled with the same soil mix and saturated with water until it runs out, after the draining stops, the water table will be at exactly the same height in all the pots. This (perched) water table (the saturated layer that does not drain out) is independent of the height or diameter of the pot, but is dependent on the soil particle size. Large particle soils drain better and hold more air and the water table is lower as there is less surface area and less adhesive attraction of water.
Practical point: I used to use seedling punnets for the first potting up of rooted cuttings and always lost some 7-10 days later, or they failed to thrive. Punnets are 2-3cm lower in height than the 7-8cm square pot, and in punnets the roots of a cutting are almost always exposed to or are very near the water table. My results have much improved since switching to7-8cm square pots for the first potting-up. The young 3-4cm roots are initially well above this non-draining water table, so drowning the new roots is much less likely. Commercial growers pot up rooted cuttings straight into 15cm pots for labour saving reasons; they rarely lose plants at this stage!
Signs of overwatering: Wilted plants in a heavy pot do not need water: they are already overwatered and the root hairs are at serious risk of dying if not dead already due to lack of air. The sick/dead root hairs are unable to absorb water and the plant wilts. Giving more water to a wilted plant in a heavy pot is fatal. Wilted plants in a light/dried out pot DO need water.
To rescue an overwatered plant try the following:
• Place the pot at an angle: if water drips out of the lowermost drainage hole it has been overwatered. Allow the excess to drain away. The water table will drop as it shifts to remain horizontal at the same depth over the now lowermost drainage point.
• De-pot the plant and place it on newspaper to dry out the soil mix, but not for longer than a few hours so as not to further damage the roots through exposure. Roots can regenerate if not too far gone, but the plant may not thrive for a while and drop some leaves.
• Insert a wick, like a strip of synthetic chamois cloth, synthetic shoelaces, twine etc folded over the end of a screwdriver and pushed 3-4cm into the soil through a drainage hole and allow it to hang free 5-10cm below the pot. Excess water will drip out and air will replace it.
How to water correctly:
• Look at weather report and adjust your watering schedule accordingly.
• Assess the weight of the potted plant frequently so as to be familiar with it, and water accordingly.
• If the surface of the soil mix is greyish and water does not readily seep into a soil when watered, it confirms the surface is crusted and the plant is likely dry.
• Sticking your finger or a kebab stick into the soil mix is not so practical but can be tried: dry soil does not stick.
• Water meters inserted well into the soil mix to measure the water content are expensive, may injure the roots and are not all that reliable.
• The risk of overwatering is greater in small plants; always water for the size of the plant and not the size of the pot.
• Wet the floor or mist to increase the humidity and cool the environment.
• The growing area should be well ventilated.
• Keep drainage holes open by using plastic mesh or coffee filter over the holes on the inside. Place pots standing on solid surfaces on a plastic mesh to ensure drainage.
• Use polyacrylamide crystals: Stockosorb is a cross-linked acrylamide and potassium polyacrylate co-polymer. It retains water and dissolved nutrients in gel form and releases both water and nutrients to surrounding compost as it dries, making them available to the plant. It reduces losses from leaching, evaporation and surface run-off, thus reducing the need for watering. The repeated swelling and shrinkage of the hydrogel creates pore spaces for aeration, water permeability and root growth, thus improving soil structure. Recommended dosage is 1gm per litre of compost: it must be mixed into the growing medium just before use.
• Horticultural vermiculite is used in its exfoliated form (Cape Agricutural Products, Sergeant Street, Somerset West medium grade R104.50 for 8kg and fine grade R108.50 for 9kg). The concertina-shaped granules are insoluble and provide both water holding capacity and aeration through its large surface area in the layers. Water and air are stored within the inter-laminar voids as well as between the particles. It holds >70% water at saturation and is mixed in with the other components of the growing medium. Vermiculite is sterile, extremely lightweight but has no nutritional value. Absorbent rock will increases aeration and drainage.
• Perlite is volcanic glass which when superheated expands greatly. Perlite aerates the soil better, but is less water-retentive than vermiculite: it may be used as an alternative.
• Saturaid lowers the surface tension of water, thus allowing it to distribute more evenly throughout the pot or basket and with it the dissolved nutrients– resulting in less water run-off and leaching of nutrients, and it decreases the need for watering. It lasts for a few months and is best mixed with the growing medium, but can be sprinkled on the compost surface – 2 level teaspoons for a 20cm pot or 3 teaspoons for a 25cm basket.
• Baskets are more likely to be under watered. To conserve water, place a small saucer in the bottom of the coir basket or, if lined with plastic, make the drainage holes a little above the lowest point.
• Fuchsias do not like their roots hot: in very hot weather use double potting with an insulating material such as vermiculite and or sand, compost or even newspaper between the outer and inner pot. Clay pots keep roots cool by evaporation form the porous sides. Set baskets or pots on floor where it is cooler during very hot weather.
• A pebble saucer is useful to increase immediate humidity, taking care the pot is placed on top of the pebbles and not in the water.
• Avoid the plant becoming root bound, as the root bulk restricts the water holding capacity and will stunt the plant. Compaction and a root-bound plant need to be re-potted at least once every three years.
• The chemicals in tap water and fertilisers accumulate as water is removed by the plant or by drainage. The resulting increase in osmotic forces will prevent the plant from absorbing water and dissolved nutrients, causing ‘fertiliser burn’. It is best to water thoroughly from time to time, until it runs out, so that excess chemicals and fertilisers are leached out. I water thoroughly the night before the weekly fertilising of plants, and the next day I only give enough for the size of the plant and try avoid it running out, this is more economical and avoids too much concentration of chemicals.