How to Grow Geranium Pelargonium
From the Greek pelargos, a stork, referring to the resemblance between the beak of the fruit and that of a stork (Geraniaceae). This is the correct name for the plant which is grown in public parks and our gardens and greenhouses. The zonal pelargoniums have in the past 70 years mostly been called ‘Geraniums’ which is a complete misnomer. The true Geraniums were described in an earlier article.
Within the past 10′ years the horticultural public has been made aware of the misnomer, mainly by the efforts of the specialist societies throughout the world, and are now using the correct term for the zonal and regal pelargoniums in increasing numbers.
To help to sort out the confusion that has existed, it is worth stating that the cultivars of the genus Pelargonium, both regal and zonal types, have definitely been bred from the true Pelargonium species and not from the genus Geranium; this is the key to the correct definition.
In the genus Pelargonium there are over 300 recorded species; this does not include the sub-species and other varieties not recorded yet, of which there must be a considerable number.
The species are identified in one way by the fact that the plants breed true from seed, although some have individual races within the species which also breed true from seed, and a lot of cross-pollination is done by insects on plants growing in their natural habitat, causing much confusion among taxonomists. Many of these natural hybrids are very closely identified with the original plant but may have slightly different leaves, form or flowers.
The species were mainly brought to Europe from many parts of Africa, although several places in other parts of the world such as Australia, New Zealand and Tasmania have also contributed during the last three centuries. They are not hardy in cooler zones and have to be protected during the winter months, although a wide range of species is grown out of doors in some places.
What is remarkable is that such a large number of colourful cultivated varieties could ever have been bred from plants that have only very small flowers. It shows the tenacity and enthusiasm of the breeders who performed this task, mainly during the last century, although this work has been carried on into the present era.
The species are fascinating to explore, and there is no doubt that they are more important than the cultivars in many ways, especially in their use for hybridizing purposes and also for experimentation and research.
There are many kinds of fantastic shapes and forms among the various kinds and a great number have perfume in their leaves. Although this scent is often clearly defined, it cannot be assessed absolutely in all varieties because so many factors which contribute to the amount of volatile oil in the tissues have to be taken into consideration. Variations of this can be caused by environment, feeding, soil structure, age of plants, time or season of year, etc., all of which can vary from county to county and country to country. One of the main reasons why smells or perfumes seem to vary is because the sense of smell varies widely between one person and another.
The volatile oil is distilled from many of the species to be used in cosmetics and perfumes.
The scented-leaved kinds are listed here because they are mainly species and thus they are easy to classify.
The leaves of the pelargonium are edible and are used a great deal in cooking and can add at least ten different flavours to any cake or sweetmeat. It is, therefore, worthwhile growing certain species for this purpose alone.
The following is a list of the species
Species cultivated P. abrotanifolium, flowers white or rose veined with purple,
P. angulosum, plant hairy, leaves 5-lobed, flowers purple, veined maroon. P. australe, flowers rose or whitish, spotted and striped
The ‘Uniques’ are another group that have sprung up in recent years and are stated to be P. fulgidum hybrids. P. fulgidum, a sub-shrubby species with bright red flowers, is prominent in their ancestry. They are best grown in pots and hanging baskets. There are many different perfumes in the leaves of the varieties listed below:
‘Crimson Unique, red and black flowers; ‘Scarlet Unique’, lemon scent, red flowers, parent of ‘Carefree’ and ‘Hula’ ; ‘Paton’s Unique’, verbena scent, rose flowers; ‘Purple Unique’, peppermint scent, purple flowers; ‘Rose Unique’, rose scent, rose flowers; ‘White Unique’, white flowers with purple veins. Cultivars: one of the most important sections of the cultivars are the regal or domesticum Pelargoniums which have very beautiful flowers and green leaves, but recently some sportA have been discovered with golden and green bicolor leaves which should make these beautiful plants much sought after if hybridizers are successful in breeding these coloured leaves into this section.
The main parents of the regals are P. cucullatum and P. betulinum which are indigenous to the coastal regions of South Africa. Hybridization started on the species mainly in England and France and also in central Europe well over a century ago. These plants should be grown under glass or in the house throughout the year in cool areas, although they may be grown out of doors in summer in exceptionally protected places. Two lovely cultivars have been produced that will grow well out of doors in all kinds of weather during the summer months. These are ‘Hula’ and ‘Carefree’ from America. These two are the result of crossing the cultivars back to the species. ‘Hula’ and `Carefree’ do not have flower umbels as large as the true regals but have the advantage of being able to stand up to bad conditions out of doors.
Some recommended cultivars are as follows (dominating colours only are mentioned): `Annie Hawkins’, pink; strawberry pink and white; `Blythwood’, purple and mauve; ‘Caprice’, pink; ‘Canisbrooke’, rose pink; `Doris Frith’, white; ‘Grand Slam’, red; ‘Marie Rober’, lavender; ‘Muriel Hawkins’, pink; ‘Rapture’, apricot; `Rhodamine’, purple and mauve; and the outstanding sport from ‘Grand Slam’, ‘Lavender Grand Slam’.
The flowering season of the regals has been greatly lengthened within the last five years by the introduction of the new American cultivars.
A great advantage in growing plants in this section is that they are rarely troubled by disease. The worst pest is the greenhouse white fly which appears at all times and can spread rapidly. It can, however, easily be controlled by using a good insecticide.
The section which dominates the genus consists of the hortorums, usually referred to as zonals. These are divided into many groups which are classified as follows (selected cultivars are listed under each heading):
Single-flowered group (normally with not more than five petals):
‘Barbara Hope’, pink; ‘Block’, scarlet; ‘Countess of Jersey’, salmon; ‘Doris Moore’, cherry; ‘Elizabeth Angus’, rose; ‘Eric Lee’, magenta; ‘Francis James’, bicolor flowers; ‘Golden Lion’, orange; ‘Highland Queen’, pink; ‘Maxim Kovaleski’, orange; ‘Mrs E. G. Hill’, pink; ‘Pandora’, scarlet; ‘pride of the West’, cerise; ‘Victorious’, scarlet; ‘Victory’, red. Semi-doubles :
American Irenes of various shades and colours are extremely useful for bedding purposes; many named cultivars are very similar to each other. Other cultivated varieties include `Dagata’, pink; ‘Genetrix’, pink; `Gustav Emich’, scarlet; ‘King of Denmark’, pink; ‘Pink Bouquet’, pink; ‘The Speaker’, red.
‘Alpine Orange’, orange; ‘A. M. Maine’, magenta; ‘Blue Spring’, red-purple; ‘Double Henry Jacoby’, crimson; ‘Jewel’, rose; ‘Jean Oberle’, pink; lerchenmuller’, cerise; `Monsieur Emil David’, purple; ‘Maid of Perth’, salmon; ‘Mrs Lawrence’, pink; ‘Paul Reboux’, red; ‘Rubin’ red; ‘Schwarzwalderin’, rose; Trautleib’, pink. Cactus group (single or double flowers with quilled petals):
‘Attraction’, salmon; ‘Fire Dragon’, red; ‘Mrs Salter Bevis’, pink; ‘Noel’, white; ‘Spitfire’, red with silver leaves; ‘Tangerine’, vermilion.
Rosebud group (flower buds tight and compact, centre petals remaining unopened, like small rosebuds):
‘Apple Blossom Rosebud’, pink; ‘Red Rambler, red; ‘Rosebud Supreme. red.
‘Aide’, pink; ‘Caligula’, red; ‘Cupid’, pink; ‘Goblin’, red; `Jenifer’, carmine; ‘Grace Wells’, mauve; ‘Mephistopheles’, red; ‘Mandy’, cerise; ‘Pauline’, rose; ‘Piccaninny’, red; ‘Taurus’, red; ‘Timothy Clifford’, salmon; ‘Wendy’, salmon; ‘Waveney’, red.
`Blakesdorr, red; ‘Emma Hossler’, pink; `Fantasia’, white; ‘Miranda’, carmine; `Madam Everaarts’, pink; ‘Pixie’, salmon. Fancy-leaved group (the colours given are those of the flowers):
Silver leaves: ‘Flower of Spring, red; ‘Mrs Mappin’, red; ‘Mrs Parker’, pink; ‘Wilhelm Langguth’ (syn. ‘Caroline Schmidt’), red. Golden leaves: ‘Golden Crest’ ; ‘Golden Orfe’ ; ‘Verona’.
Butterfly leaves: ‘A Happy Thought’ ; Crystal Palace Gem’ ; ‘Madame Butterfly’. Bronze bicolour leaves: ‘Bronze Corrine’ ; ‘Bronze Queen’ ; ‘Gaiety Girl; ‘Dollar
Multi-coloured leaves: ‘Dolly Varden: ; ‘Lass o’ Gowrie’ ; ‘Miss Burdett-Coutts , ‘Henry Cox ; ‘Mrs Pollock’ ; ‘Sophie Dumaresque . Ivy-leaved group:
One of the best in this group is P. peltatum, the original species from which this section has been derived. Cultivars are: ‘Abel Corriere’, magenta; ‘Beatrice Cottington’, purple; ‘Galilee’, pink; ‘LaFrance . mauve: L Elegante’, leaves cream and green with purple markings; ‘Madame Margot’, white and green leaf; and two with green leaves and white veins, ‘Crocodile’ and ‘White Mesh’.
In general the large-flowered cultivars described above will grow under normal garden and greenhouse conditions as will the coloured-leaved cultivars, which benefit from being left out of doors during the summer months to get full sunshine and rain.
The miniature and dwarf sections are best grown in the greenhouse in pots, or they are very useful plants to grow out of doors in containers such as window boxes or urns. They are especially good for hanging baskets when used in conjunction with ivy-leaved kinds.
Hanging baskets are very useful for enhancing a display out of doors, especially under porches. One of the best cultivars for this purpose is ‘The Prostrate Boar’, a newer introduction which grows very quickly and produces an abundance of flowers throughout the summer. Make sure that you get the prostrate type and not the ordinary `Boar’ which does not grow so vigorously, nor flower so freely. `The Boar’, or P. salmonia, is inclined to grow vertically.
P. frutetorum has had in the past, and shouldhave in the future, a great influence on the pelargonium genus because of its great vigour and its ability to influence the pigments in the leaves of the many cultivars crossed with it.
Hybridization merely consists in taking thepollenfrom one flower andtransferring it on to the stigma of another compatible cultivar. This method will give some good results, but if you are going to go in for a proper breeding programme, you should isolate those plants intended for breeding purposes and keep clear records of each individual cross. This is very necessary should any of your seedlings turn out to be good ones and you wish to register them as new introductions. The miniatures and the dwarfs are very adaptable for cross-breeding, so it is advisable to work on these for primary experiments.
Cultivation In general pelargoniums grown in pots will do well in most good potting composts, though it is advisable
Pelargoniums should never be over-potted. When repotting becomes necessary it is often possible, by removing old compost and slightly reducing the size of the root-ball, to repot into pots of the same size; otherwise the plants should be moved into pots one size larger only.
They should always be potted firmly.
Although plants should be watered freely during the growing period in spring and summer, they should never be over-watered and, in any case, the pots in which they are grown should be properly crocked and the soil mixture should be free-draining so that surplus moisture can get away quickly, otherwise various root-rots and stem-rots may be encouraged. In winter plants will need little water, though the soil in the pots should not be allowed to dry out.
Some shading will be required in the greenhouse from late April or early May onwards. A light application of `Summer Cloud’ or other proprietary shading compound to the glass will be sufficient.
In order to prevent damping-off of the flowers the atmosphere in the greenhouse should be kept as dry as possible during the summer. This means that proper use should be made of the ventilators and that every attempt should be made to keep the air circulating to avoid an over-humid stagnant atmosphere. During the winter, when it is equally important to keep the air dry but warm, good circulation can be provided by using an electrical blower heater.
To keep the plants growing freely and to maintain good leaf colour it is necessary to feed them during the growing season. Regular weak applications of proprietary liquid fertiliser should be given from about a month after the plants are in their final pots, until September. It should be noted, however, that plants in the fancy-leaved group should either not be fed at all, or the feed they are given should not contain nitrogen. These kinds should, in any case, be given less water than others.
A number of zonal varieties can be induced to flower in winter, when blooms are always welcome. The method is to take cuttings in the spring, by normal propagation methods described below. The young plants are grown on steadily during the summer and all flower buds are removed until late September. Plants treated’ in this way should flower throughout the winter months. It is best to maintain a minimum temperature of 60°F (16°C) and the plants should be given as much light as possible. During the summer the plants may be placed in a sunny cold frame or the pots may be plunged in a sunny, sheltered place out of doors. They should be brought into the greenhouse in September.
Plants which are to be used for summer bedding purposes are raised from cuttings taken in August or September, rooting several in each 5-inch pot, or in boxes, spacing the cuttings 2 inches apart. In February the rooted cuttings are potted into individual 3-inch pots and kept in a temperature of 45-50°F (7-10°C) until April. They are then hardened off in a cold frame before planting them out of doors in late May or early June, when all danger of frost is over. Do not plant shallowly; it is best to take out a hole large enough and deep enough to take the plant up to its first pair of leaves. Leggy plants may be planted more deeply. Remove dead leaves and flowers as soon as they are seen and pinch out long, unwanted shoots from time to time to keep the plants bushy. Keep the plants well watered in dry weather. A gentle overhead spray in the evenings in hot weather is beneficial. In September, before the first frosts, the plants should be lifted and brought into the greenhouse for the winter. The shoots should be cut back, long roots trimmed and the plants potted into small pots. The minimum winter temperature in the greenhouse should be around 42°F (5°C).
Propagation of regal pelargoniums is by cuttings, which, like those of the other types, root easily. They should be about 3 inches long, taken from the top of the lateral shoots. They are trimmed back to a node and the bottom leaves are removed. They will root quickly in a sterile rooting compost, in pots or in a propagating frame in the greenhouse. Bottom heat is not required. Cuttings of this type are usually taken in July or August.
Propagation of the hortorums or zonal pelargoniums may be effected in several ways. Cuttings of the type described above may be taken and either rooted singly in 24-inch pots or three cuttings may be inserted round the edge of a 3-inch pot. If large numbers are to be rooted they may be inserted in a suitable rooting compost in a frame, or 2 inches apart in shallow boxes. Cuttings are usually taken in June, July or August in this country, to enable them to form roots early. If they are taken later they may not root properly before the end of the season and thus may be lost. However, they may be rooted later in a propagating case in the greenhouse, and commercially they are rooted in quantity by mist propagation methods, using bottom heat.
The leaf-axil (or leaf-bud) method of taking cuttings has become popular in recent years. This consists in taking a leaf and 0.5 inch of stem from the parent plant, inch above and below the node or joint. The stem section is cut vertically through the centre of the stem. The cuttings thus formed are inserted in rooting compost in the normal way, just covering the buds. If some bud growth is seen in the leaf axils you are more certain of rooting the cuttings. Such cuttings are normally taken in the summer months.
Whichever method you adopt, make sure that you use clean stock only. Almost any piece of a zonal pelargonium containing stem and leaves can be used for propagation purposes, provided the conditions are right. It is quite normal to root stem cuttings of these plants out of doors during the summer months, in the open ground.
Plants may also be raised from seed obtained from a reliable source. It is unwise to buy unnamed seedlings as they may produce large plants with few flowers. Seeds should be sown 1/16 inch deep in light sandy soil, in pans or boxes, in the greenhouse, from February to April, in a temperature of 55-65°F (13-18°C).
Tuberous-rooted pelargonium species may be divided in spring for propagation purposes.
The principal pests of pelargoniums grown under glass are aphids and greenhouse white fly. These may be controlled by insecticidal sprays or by fumigation methods. The disease variously known as black leg, black rot, black stem rot or pelargonium stem rot, is very liable to attack cuttings and sometimes mature plants. It first appears on the lower part of the stem, which turns black. It spreads rapidly up the stem and soon kills the plant. It seems to be encouraged by too much moisture in the compost and in over-humid conditions. Some control may be obtained by spraying or dusting plants with captan in the autumn. It is also important not to damage the skin of the stem when taking cuttings, otherwise disease spores may enter through the skin at this point. Always use a sharp sterile knife or razor blade when taking or trimming cuttings.
Grey mould (Botrytis cinerea) will attack plants under glass, especially in close, humid conditions. It appears as a grey furry mould an stems, leaves or flowers. Proprietary fungicides based on copper or thiram will control this disease, but it is more important to maintain the correct conditions in the greenhouse, with ample ventilation and a dry atmosphere. When plants are overwintered remove all dead, furry leaves, but make sure that the leaf is quite dead. When taking away discoloured leaves do this by removing the leaf only at first, leaving the stalk intact until the abscission layer has formed between stalk and stem, when the stalk may be removed easily. To attempt to remove it before the abscission layer has formed will result in the stem being damaged with the consequent risk of disease spores entering.