The Vernon Geranium Nursery

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Caring for Geranium Plants

We are sometimes asked for advice as to why some plants have died or failed to thrive, but it is unlikely that we can pin-point exactly what the trouble was from our desk here. Plants are living things, and like animals and people they can suffer from a myriad of physical ills. It is always disappointing when animals or plants do not do well, but a one hundred per cent success rate is sometimes difficult to achieve. As to why some plants should die and others next to them thrive, this is the mystery of life! Why does one cat in a litter die? Or one person contract an illness while the next person does not? We try to be as helpful as possible, so we hope these indications will help to identify what might have caused trouble.

The Ideal Growing Environment

The pelargonium family originated mainly from South Africa, where they enjoy high light levels and a dry atmosphere. The main things to consider are compost, light, feeding and watering.

It is essential to keep the plants in a dry, frost free atmosphere, because if they are cold and damp they are likely to rot. However, this does not mean keeping them dry at the roots. When you see long stalks that have a little bit of growth right at the top on people’s windowsills, you can be sure that you are looking at a plant that was kept bone dry in the winter! We do find that watering can be a problem. Because the pelargonium family do not like cold and damp conditions, we find that lots of people are very sparing with the water. In the growing season they do, in fact, need to be well watered, but in a situation where the pot is well drained, and where water is not going to be splashed all over the foliage.

Some of the peat composts sold in Garden Centres stay rather soggy, so it is always a good idea to add some grit, and always make sure the holes in the pot are left clear of any obstructions so that excess water can drain away. The problem might well have been in the compost, because it really needs to be freshly made for all the nutrients to be active.

Of course, garden soil is not sterilised, so anything can be lurking there. The ornamental leaf type are more difficult to grow than the green leaved ones because there is much less chlorophyll to support the growth of the plants, which means they are slower to develop and need high light levels. Sometimes the reason for growing these plants is to enjoy the colour of the foliage, especially the tricoloured ones – the flowers are a bonus. Because there is no chlorophyll at all in the white or cream parts of the leaf, they are vulnerable to scorching in bright, hot sunlight, such as might arise on a sunny windowsill, or in a greenhouse or conservatory. So shading in the middle of summer is a good idea. In the winter they need the best light you can give them, and never let the roots dry out. Dry roots equals stressed plants!


When we have a summer of low light levels and cold, wet soil, it certainly does not help. The varying weather conditions is why it is not always possible to get the same results every year. We always say that if it is a bright, warm summer the geraniums do well, if it is dull and wet the fuchsias do well, and if it is a mixture, then they both do well!

Feeding your plants

If they are given too much nitrogen, the plants make plenty of leaf, but few flowering buds. They also tend to make soft growth, which is more susceptible to rotting in damp conditions. We once had leaf damage on our regal pelargoniums because we had put slow release granules in the compost, and then continued to use liquid feeds, both of which had trace elements included. They then showed signs of boron poisoning i.e. we had given too much of the trace elements needed by the plants.


  • Mice! - We once had a letter from a frantic customer who said her plants in the conservatory were keeling over from above the soil level. In fear and trepidation, in case we upset her, we phoned and suggested she might have mice in the conservatory. "Do you know! I think you might be right!" she said. Phew!
  • Vine weevil - This is a pest which seems to be on the increase and is difficult to eradicate. We know that fuchsia growers are very concerned about it. A garden centre is the place to go to for advice on suitable chemicals to combat the pest. We think they will probably recommend a product from PBI called "Provado", but they might have other suggestions. We know of one nurseryman who recommends letting bantam chickens loose in the greenhouse! Levingtons do now produce a compost that will kill vine weevil, but that would entail washing the roots and repotting everything. We are sorry there is no magic remedy to this problem.
  • Whitefly - These pests can be a problem with the regal and sometimes the scented pelargoniums. 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!
  • Caterpillars – There is a moth that can appear about August or September that will chew the leaves of the zonal geraniums which needs catching in the evenings or eradicating with a systemic insecticide.
  • Sciarid fly larvae – These 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.

Other Possible Problems Affecting Your Geraniums

  • Stem Rot - Alas, stem rot 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.
  • Leafy gall - 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!
  • Pelargonium rust - This can affect the zonal varieties, and it is getting everywhere nowadays – it first came into the country in 1968 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 advise spraying with a fungicide called Bio Dithane945, or with Tumbleblight, both of which are obtainable at most Garden Centres. 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.
  • Grey Mould (botrytis) - This can be 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.
  • Oedema - Ivy leaf geraniums never have rust, only zonals are ever infected. If you see brown marks on the backs of the leaves, 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.
  • Yellowing of the bottom leaves - This can occur for a number of reasons:
    1. Insufficient light is reaching the lower part of the plant. This is probably the cause of the problem if the plants are too close together, or are too far from a good source of light. If you use a photographer’s light meter, you will discover that three feet in from a window will reduce the light level by 50%!
    2. The plants are receiving insufficient water at the roots. Although all of the pelargonium family will rot in a humid atmosphere, it is a mistake to think that they need to be kept dry at the roots. They are never dormant, so require moisture all the year round to transpire, but less, of course, in winter and in dull weather. When bone dry the stems go hard and woody, and the plant never grows as well – it is always best to renew the plant with fresh cuttings when this has occurred.
    3. The plants are drowning! Too much water will exclude the oxygen from the roots, causing them to die. It is said that 90% of house plants are killed from over watering. Never be afraid of taking a plant out of it’s pot to see what is happening to the roots. Sometimes it is possible to take a cutting off the top of a plant if it is only rotting at the bottom.
    4. The plants have been moved recently and are adjusting to their new environment.

Expert Advice

Another point to watch is that it is never a good idea to put the same plants in the same spot every year – it is good farming practice to rotate crops, which is better for the soil.

Do not worry too much about removing leaves from pelargoniums, they will always grow new ones, but it might give the plant a "leggy" appearance. The answer to this is to either take cuttings to make new plants, or to cut the plant back to make it shoot out from lower down (and take cuttings from the top pieces!). If a plant looks unwell, it is always a good idea to take it out of its pot, or the ground, to see what is happening down below. Plants can often be saved by taking off all the soil and re-potting into fresh, and sometimes a cutting can be taken from the upper part that will root successfully.

No end of times when people bring dead plants for an assessment we find that they have been potted up into rock-hard compost. Our advice is always to keep the compost light and fluffy – and we are very much in favour of adding 20% in volume of perlite. Our expert's comment was, "People have been watching too many gardening programmes where the plants have been placed in the ground and then firmed in with the heel of the boot." However, this is not the way to deal with pot plants. "Fill and tap – NEVER push the compost down round the roots. We once had a high number of plants rotting off in the nursery – the problem was traced back to one of the "potters" – so it was back to the training session!

Ensure that the compost is not too soggy, try mixing in some grit to improve drainage

Ensure that the compost is not too soggy, try mixing in some grit to improve drainage.

Overfeeding your plants can make plenty of leaf, but few flowering buds

Overfeeding your plants can make plenty of leaf, but few flowering buds.

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