Geraniums are usually the toughest, most enduring plants in any garden. In one place I was living, we had a geranium actually growing through the concrete around the house. With a bit of local research, I discovered that it was a remnant of a previous cottage garden from the 1920s that had outlasted the entire neighborhood.
Geraniums are grown all over the world. They are perennials with some characteristics of succulents, having soft, fleshy leaves, and the unpredictable growth habits that make them true architectural plants. Members of the pelargonium family, they’re particularly easy to manage, with no bad habits in the garden.
Geraniums are usually grown from cuttings, although some cultivars are grown from seed. Cuttings root easily and establish best in well-drained soil, preferably raised slightly. They can also be grown in hanging baskets and pots. One of their most useful attributes is their adaptability to various conditions in the garden, and they are a good choice for a trustworthy plant for problem areas, except particularly wet places.
Preparation of beds for geraniums is pretty easy. The soil should be friable, not impacted, and an all-purpose fertilizer, preferably seaweed, is suggested for basic nutrition for the seedlings or cuttings, particularly in normal soil where basic nutrition levels can vary considerably. (I’ve never lost a plant using seaweed.)
As the plant matures, a basic regime of regular fertilizer application is required. Geraniums require a reliable supply of nitrogen during the growing season, and fertilization each month. Slow-release nitrogen fertilizer is recommended to avoid the effects of nitrogen leaching after heavy rain.
Mature plants take up a bit of room, so allow roughly as much space for a full-grown geranium as you would for a rosebush. A layer of mulch, preferably heavy types of mulch with a slow breakdown, will keep down weeds and stabilize the soil surface, adding “body” to the basic soil mix. It also helps prevent water splash on the plants and formation of fungal cultures on the leaves by transfer.
This is personal taste, but geraniums should not be bunched together. They prefer open space and have a surprising growth rate that can create difficulties if they have to compete for territory. There’s an added risk factor in that when too many plants of one type are in one place, pests and diseases can spread much more easily. This can become a serious problem if one plant is shading another, and the weaker plant becomes infected.
They require sunlight, about 6-8 hours, and shelter from strong winds. Check the prevailing wind in your location, and plant the geraniums in sheltered positions relative to it. They’ll get some wind, but air circulation is necessary because the air removes dust and pathogens from the plants. They can tolerate dry periods but should be watered regularly. When watering, it is advisable not to saturate the soil or splash water on the plants. Use a small watering can with a gentle flow of water.
In pots and baskets, regular water and appropriate fertilizer will deal with most of the plant's needs. Do not (ever) allow the plant to become pot-bound. The same basic practices of sunlight, watering, and care apply to container-grown geraniums. Be very wary of any appearance of fungal blights. (See below)
Fungi are the biggest, most frequent danger to geraniums. Their effect is rapid and pernicious. Discoloration of leaves or degradation and shriveling of stems is almost certainly fungal infection. Remove all affected parts of the plant. If the plant doesn’t recover fairly quickly, like in a week or so, remove the plant.
Be ruthless, because diseased plants can infect the soil too. If that’s the case, dig up the soil around the plant, and remove that as well. Sterilize garden equipment used to remove diseased plants and soil. Fungi can remain in soil for some time and will definitely create problems for other plants, particularly seedlings, given a chance. They can also transfer from the spade or secateurs to new locations.
Fungal infections are prevented by removing dead leaves and anything around the plant that can get wet and allow fungi to attack the plant. Weeds should not be permitted to grow near the stems, because they can help transfer fungal spores and insect pests.
Geraniums can suffer from mosaic virus, leaf spot, and some quite bizarre distortions of the plant that make it look “twisted.” Other growths or deformities also indicate infection. Remove the plant immediately, and incinerate all plant material. Soil replacement may also be advisable, as per the fungal infections.
Fungal and viral infections of plants can destroy gardens. No amount of effort to avoid contamination is too much. Strict sterility of gardening equipment, including gloves, clothing, and boots, is highly recommended.
Yellowing leaves are the sign of lack of nitrogen. Immediate application of fertilizer is required, with a strong percentage of nitrogen in the NPK mix, or a nitrogen-specific fertilizer. Recovery from the deficiency can be slow, and it also increases the risk of disease. Same procedure as for fungal disease if the plant is dying or dead. (You can assume that some opportunistic pathogen has taken advantage of the weakened state of the plant.)
Root-knot nematodes can affect geraniums, usually in hot weather. I’ve read that relocation of the plants to a sterile pot or another garden bed is the usual method of control. Fine, as far as it goes, but you’ve still got a problem in the original garden bed and may be spreading it, or the area may have a high population of nematodes. My view is that plant-parasitic nematodes are entirely unacceptable in a garden. I’m not entirely sure why these well-known pests are considered ineradicable, but they’re not likely to go away.
The geranium has in fact given you useful information in finding the nematodes. If a nematode attack affects them, it will also affect related plants, like pelargoniums. It also tells you that annuals, which are dependent on their life cycle running more or less according to plan, are potentially at risk. Early warning of the presence of the nematodes is extremely helpful for the garden as a whole.
Nematodes are a persistent plague, at their worst. If you do nothing, you’re stuck with them. They’re highly destructive and likely to give you a bed full of weak, suffering, poorly rooted plants. Healthy plants can fight nematodes, but those infected are simply adding to the problem.
I suggest complete eradication of the nematodes, either by soil removal or by specific anti-nematode treatments, which greatly reduce their numbers. Soil solarization is the method recommended for home gardeners. Planting nematode resistant plants is another tactic. Some tomatoes, for example, are bred specifically for their resistance to nematodes, commercially known as “V” cultivars. The nematode resistant plants inhibit the population of nematodes from exploding.
One of the reasons I so often emphasize various degrees of plant and soil removal in gardens is because I’m a horticulturalist. I simply do not believe that pathogen-infested soil is tolerable. It’s certainly never safe, and re-infestation is almost certain. Unfortunately, cultivation methods can drastically increase the spread of pathogens.
It’s a regular feature of all forms of gardening that there are places where plants don’t grow. As a matter of fact, the pre-existing dead zones in gardens are a good map of where to expect problems. You can safely assume that if even weeds won’t grow in an area of your garden, there’s some good reason. You’ll note that formal gardens are actually grown from scratch, with their own bedding, and a cultivation regime specifically designed for them.
The only real defense against fungi, viruses, and nematodes is healthy soil biota, and infected soil, by definition, is not healthy. Severely infected soil is a liability to everything around it. Local measures often aren’t enough. Anti-fungal treatments are only temporary, viruses are sporadic, but nematodes are endemic and can infest whole gardens. It’s a question of the scale of the problem.
Insect pests of geraniums include whitefly, mites, caterpillars, and subterranean termites. Commercial sprays are usually adequate, but severely affected plants are also susceptible to disease, and the same considerations apply.
Be extremely careful of strong pesticides, and always use them strictly as directed. They are toxic and can do serious damage. Wear gloves, and do not allow skin, nose, mouth, or eye contact.
Geraniums are inclined to be vulnerable to weeds that are too close to them. A weed mat is the easiest and most thorough method of preventing and removing weeds. It will smother weed growth and allow the geranium some space around its roots and stem.
Geraniums will grow in most climates. Common wisdom in cold climates is that they will survive over winter, but that they will also shelter diseases, so they should be replaced annually. That may be the case, but the logic could take another look. If a perennial plant has survived a winter, why is it somehow less viable than it was, purely because it survived?
Geraniums can live for many years in variable conditions almost anywhere on Earth. I don’t quite see the rationale. On that basis, you’d get rid of the trees, too. The only thing I would suggest is that in cold zones, the snow melt could have some unwanted effects if water sits around the plants.
The geranium is one of my favorite plants. The more different varieties you grow, the more interesting they become. They have an aesthetic of their own and are a joy in the garden—a trustworthy flowering plant that creates its own palette and enhances wherever it’s planted. Don’t be surprised if the geranium zone becomes one of your favorite places in the garden, and you find yourself naturally drawn to geraniums wherever you see them… perhaps with a pair of scissors for impromptu cuttings…