Cultivation techniques for new large-flowered geranium varieties
The large-flowered geraniums 'Coral', 'Ice Cave' and 'Scene' have a plant height of 30 to 40 cm, with round and large flower heads, good mass planting effect and few pests and diseases, making them excellent material for landscape applications. Geraniums of this type are all award-winning varieties from European flower trials.
Growth habit
They prefer a cool climate, with a suitable growing temperature of 5°C to 25°C. The plants enter a semi-dormant state during the high-temperature period in summer, and in cold winter regions they can overwinter with only slight protection. They prefer a location with ample light, tolerate dryness and dislike waterlogging, and require a loose growing medium with good drainage that is rich in organic matter.
Sow from late winter to early spring, and the flowering period runs through the entire summer. When sown in late summer and kept at an overwintering temperature above 5°C, they can flower in spring.
Sowing method
The seeds require darkness during germination, so sowing must cover them with a 3 to 5 mm thick layer of growing medium or 2 to 4 mm of coarse vermiculite. Sowing can use 128-cell plug trays, with imported peat as the growing medium, adding 10% large perlite with a diameter of 3 to 5 mm, keeping the medium moderately moist but not overly wet; germination occurs in 5 to 10 days.
Seedling management
The seedling-raising cycle is 5 to 6 weeks and is divided into 4 stages. The first stage runs from sowing to the appearance of the radicle; the second stage runs from the appearance of the radicle to the unfolding of the cotyledons, when germination is complete and one true leaf has grown. After emergence, the moisture level of the growing medium should be reduced to favour root development. The third stage runs from the appearance and beginning of growth of one true leaf until the transplanting standard is reached. The fourth stage is preparation for transplanting or storage and transport. In the first stage the germination temperature is 21°C to 24°C, requiring 3 to 5 days, and the medium must be moderately moist. In the second stage the temperature is 21°C to 24°C, fertiliser can be applied once a week, alternating fertilisers with an N:P:K of 15:0:15 and 20:10:20 at a concentration of 50 to 75 ppm, requiring 5 to 10 days, with the medium moderately moist. In the third stage the temperature is 18°C to 21°C, the fertiliser concentration is 100 to 150 ppm, fertiliser is applied twice a week, requiring 14 to 21 days, basically reaching four leaves and one heart. In the fourth stage the temperature is 17°C to 18°C, requiring 7 days, with the same fertiliser concentration as the third stage, after which they can be planted into 14 cm x 12 cm pots.
pH value The pH of the water should be adjusted to slightly acidic, preferably 5.5 to 6.5, and the pH of the growing medium is best kept at 6.2 to 6.5.
Temperature Throughout the seedling-raising period, the growing medium temperature should preferably not be lower than 18°C; too low a temperature hinders the growth and development of the seedlings.
Light After germination, the seedlings should quickly receive light to prevent leggy growth. During the seedling-raising period, 16 to 18 hours of light per day can be maintained for 4 weeks, with a light intensity of 3200 to 5400 lux. Geraniums like light, and the more light there is, the more they grow. Fertiliser Fertiliser is imported American Miwo, with an N:P:K of 20:10:20; to obtain a 100 ppm fertiliser, 0.5 g of this fertiliser should be added per litre of water, and other concentrations are adjusted accordingly. If Miwo has an N:P:K of 15:0:15, to obtain a 100 ppm fertiliser, 0.67 g of this fertiliser should be added per litre of water, and other concentrations are adjusted accordingly.
Water Keep the growing medium in a moderately moist state, and keep the medium in a dry state between two waterings, while also keeping the air humidity low to reduce the occurrence of disease. If the chlorine concentration in the growing medium exceeds 1 ppm, it may cause toxicity to the cotyledons and produce immature leaves, so care should be taken to avoid using tap water with excessively high chlorine.
Pest and disease control After the cotyledons have grown, spray once a week with a 1000-fold dilution of chlorothalonil or thiophanate-methyl to prevent damping-off, spraying 2 to 3 times in succession.
Seedling stage management
For the potting medium, peat and garden soil can be mixed at a ratio of 1:1, and adding a certain amount of organic fertiliser gives better results. Immediately after planting, water with a 1000-fold dilution of thiophanate-methyl to settle the roots, which can prevent the occurrence of root rot. During cultivation, the plant shape can be made full without pinching.
Light Keep the growing environment in a full-sun state so that the plants grow well and flower as early as possible; taking advantage of the characteristic that geraniums need to accumulate a certain amount of light to flower, the flowering period can be regulated by adjusting the light, and the specific operation must be carried out according to the actual growth condition of the plants.
Temperature Geraniums prefer a cool environment and fear high temperatures; the suitable growing temperature is 5°C to 25°C, and spring is the most suitable for growth. When cultivated in autumn and winter, the night temperature should not be lower than 5°C, so in the north geraniums need the protection of a greenhouse or plastic tunnel, otherwise they are prone to cold damage. In winter, when the indoor daytime temperature is not lower than 10°C and the nighttime temperature is not lower than 5°C, they can flower continuously. In the south, summer weather is mostly hot, and geraniums are in a semi-dormant state with poor flowering; during this period the temperature needs to be appropriately lowered to below 30°C so that they can pass the summer safely. When the temperature drops in autumn, supply sufficient water and fertiliser to make them branch and flower. The leaves of geraniums have high ornamental value; removing withered and yellow leaves and spent flowers at any time and applying timely topdressing can promote a second flowering and extend the ornamental period.
Water During growth, keep the growing medium in a moderately moist state. Geraniums do not tolerate waterlogging and require the growing medium to have good aeration, otherwise the root-to-stem ratio is easily thrown off balance. Excessive water easily leads to root rot and grey mould caused by fungi; however, the growing medium should not be overly dry either, otherwise salts will accumulate around the roots and cause burning. When the medium is too dry, the lower leaves of the plant often turn pale red to yellow. The stems and leaves of geraniums have soft hairs, so when fertilising and watering, avoid getting fertiliser water on the leaves; after fertilising, rinse the leaf surface with clean water and let it dry.
Fertiliser 7 days after planting, a 600-fold dilution of a compound fertiliser with an N:P:K of 15:20:20 can be applied, once every 7 to 10 days. During growth, fertilisers mainly containing potassium, calcium nitrate and phosphorus should be used. Geraniums are very sensitive to ammonium, and the concentration of such fertilisers should not exceed 10 ppm, but in warm regions with strong light, it may be necessary to apply a fertiliser with an N:P:K of 20:10:20 to make the leaves spread out and colour well.
Disease control
(1) Grey mould
a. Main symptoms: It mainly harms leaves and flowers. At first a "V"-shaped lesion appears on the veins, on which nearly round to irregular water-soaked yellow-brown to dark-brown concentric-ringed spots appear, and the lesions sometimes produce a grey-white mould layer. When the disease occurs on the petals, they show faded spots, irregular, at first with sparse grey mould; when the weather is clear or dry the grey mould shrinks, and when humid it grows again, and the flowers turn dark red to dark brown.
b. Control method: Pay attention to ventilation and light transmission at the cultivation site, and the humidity should not be too high. In the early stage of the disease, spray the whole plant with a 1000-fold dilution of 50% iprodione or an 800 to 1000-fold dilution of 28% grey mould control agent.
(2) Brown spot disease
a. Main symptoms: It mostly occurs on the leaves, as round, nearly round to irregular lesions, light brown or grey-white to reddish-brown, with dark brown edges. The lesions on the underside of the leaf are slightly raised, with an obvious yellow halo on the outer edge; the lesions often merge with each other into larger dead spots, and finally a grey-black mould-like substance appears on both sides.
b. Control method: Keep the cultivation site ventilated and well lit; during the plant's dormant period, fertiliser and water should be controlled and not applied in excess. In the early stage of the disease, use an 800 to 1000-fold dilution of 75% thiophanate-methyl or an 800-fold dilution of 50% carbendazim or a 1000-fold dilution of 25% benomyl, spraying the whole plant, about once every 10 days, for 2 to 3 successive treatments.
(3) Bacterial leaf spot disease
a. Main symptoms: Water-soaked round to irregular sunken spots appear on the leaves, dark brown to black-brown; the lesions merge less, and in the later stage the diseased leaves wilt and curl up, hanging on the stem, and sometimes the lesions form larger necrotic angular spots at the leaf margin. Black patches are produced on the stem, while the vascular bundles and pith turn black, and the plant wilts and rots.
b. Control method: When watering and fertilising, try to avoid the growing medium splashing onto the stems and leaves, and control the medium and air humidity so they are not too high. For chemical control, a 1000-fold dilution of 53.8% Kocide 2000 dry flowable or a 2000-fold dilution of 72% agricultural streptomycin can be sprayed on the whole plant.