Geraniums are extremely tolerant plants and known for being reliable, sturdy growers that perform well with very little care needed ... which is ideal! However, from time to time problems can crop up and we have put together the following 'troubleshooting' section to help you get the very best from your plants. Thankfully there aren't many pests that are attracted to geraniums and most problems are easily treatable so don't panic if you encounter any problems - you don't have to throw your lovely plants away!
Click on the heading below which best describes the problem:
This is usually caused by caterpillars – there is a moth that can appear about August or September that will chew the leaves of the zonals which needs catching in the evenings or eradicating with a systemic insecticide. Geraniums are rarely affected by slugs and snails.
Whitefly can be a problem with the regal and sometimes the scented pelargoniums, though they do not actually damage the plant. Garden Centres are loaded with insecticides to combat this pest, but it is a case of persevering during the warm weather, as they breed very rapidly. We spend a huge amount of money to keep this pest under control – and it still pops up again! Try using "Provado", it could help here!
Greenfly are more of a problem than Whitefly, as these DO damage the plant as they can distort the leaves and spread quickly. Obtain a ‘systemic spray’ from the hardware shop (systemic just means the spray gets into the plant system and the fly eat the leaves and get the insecticide into them). Spray the whole plant, particularly under the leaves and the compost too. Best to isolate the plant if possible to stop them spreading or spray all plants so they are all protected.
These are small black flies which you will see on the surface of the compost, and their larvae can damage the roots. They can thrive in peat composts, but are not normally so active that they kill the plants. Once their life cycle moves on, they disappear, so are only a nuisance for about two months in the year. Drenching with a weak solution of Jeyes Fluid will usually put an end to them. Correct watering - keeping the soil moist but never wet - will help to keep them away.
Pelargonium rust can affect the zonal varieties, and it is getting everywhere nowadays – it first came into the country in 1964 and has gradually spread from Eastbourne, where it was first detected. It only affects the zonal types, and particularly thrives during a damp summer or autumn. However, it is not "life threatening" to the plants, and luckily it does not seem to infect the plants very rapidly, so simply removing the affected leaves will be a good control. We would also advise spraying with a suitable fungicide usually availlable at Garden Centres. Make sure you spray the underside of the leaves and the compost too so that all spores are treated. Within a day or two take off the affected leaves and either burn or put into the dustbin - do not put them on the compost heap. We do not recommend destroying your plants, as pelargonium rust is only a fungus, much like grey mould or botrytis, and is now endemic in this country, so any new plants you get will most likely suffer from it sooner or later. Ivy leaf geraniums never have rust, only zonals are ever infected.
If you see brown marks on the backs of the leaves of your ivy leaved geraniums, what you have got is not a disease at all, but a physiological disorder called Oedema. This often affects the older leaves of the ivy or hybrid ivy types and is caused by erratic watering. If the plants have got rather dry and are then watered the stomata on the back of the leaves cannot always cope, and they burst. Afterwards they callous over, so what you see is like a scar. We would suggest removing any leaves that look unsightly – the new leaves that grow will not have it. Be careful to keep the roots of the plants moist at all times, especially at the times of the year when they are growing rapidly and are transpiring a great deal. Moist, but never waterlogged, is the golden rule.
Grey mould, or botrytis, to give it it’s proper name, is a nuisance once autumn arrives. Damaged leaves or dying flowers will begin to rot once the cold, damp days arrive, and petals falling on to leaves can cause damage. The answer is threefold, one is to make sure there are no damaged leaves or flowers on the plants, the second is to supply adequate ventilation so that there is movement of air, and the third is to visit the Garden Centre to buy a fungicide designed to combat grey mould. Smokes are preferable in a greenhouse, because they do not increase the humidity, but are not practical in a porch or conservatory.
If plants are not flowering, check the following:
If plants are not thriving, check the following:
Alas, this is something that geraniums are prone to, and we find that it is more likely to happen in very hot weather. It is caused by a soil-borne fungus, and if the pot gets hot it seems to give rise to the trouble. From our experience, it also seems to occur if the plant has dried out too much, and is then copiously watered.
If you spot yellowing of the bottom leaves of your geranium plants this can occur for any of several reasons:
This is a strange, cauliflower-like growth that occurs where the stem enters the soil, and can occur on any of the pelargonium family. This problem is a complete mystery, as nobody has yet found the cause, so therefore there is no cure. It occurs completely indiscriminately – the first time we found it, in our early days of growing pelargoniums, we rushed off to a nurseryman and said "Look what we’ve found!" "Oh yes," he said, "I just break that off and throw it away." And this is still the only thing one can do. The plants continue to grow quite normally once it is removed, and cuttings taken from those plants do not necessarily have it – it just occurs as and when it feels like it!
Sometimes geranium plants suddenly collapse and die. This is know an 'Plant collapse' and has two main causes:
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