The common geranium belongs to the genus Pelargonium and has been a garden favourite since its introduction to Europe from South Africa in the 1600s. More than 200 species of Pelargoniums and many hybrid varieties exist, providing us with a wide variety of colours and leaf shapes. The geranium's attractive flowers bloom from mid spring through summer and are prized as both landscape and indoor plants. How long does it take to grow them? Several factors enter into the answer.
Types of Geraniums
Three major types of geraniums are available for sale as starter plants or seeds. Zonal geraniums are hybrids that have scalloped leaves, which also can be variegated. This type is easily grown from cuttings or seed. Ivy-leaved geraniums behave more like vines and their flowers are often smaller than other geraniums. Regal geraniums are small shrubs that sport flowers resembling azaleas---they prefer cooler temperatures than the other geraniums.
Whether you buy a young geranium at your nursery or grow one from seed or a cutting, it needs a slightly acidic soil pH---around 6.0 is recommended for most geraniums. You can lower the pH with an acid based fertiliser. To raise pH, add dolomitic limestone or hydrated lime to the soil. Do not over fertilise because this can limit flowering. Geraniums like to dry out between deep waterings but do not like to wilt, which can occur if you over water them.
Temperature Can Influence Growth Rate
Geraniums are a bit particular about the temperature in which they thrive and produce the best flowers. They are a warm weather crop that prefer night temperatures from 15.5 to 18.3 degrees C and daytime temperatures between 21.1 and 23.8 degrees C. Below 15.6 degrees C, their growth slows down and below 55 temperatures will prevent blooming. Temperatures over 26.6 or 29.4 degrees C can cause heat stress, which causes a decline in the plant's growth rate.
Growing From Seed
Many geranium varieties are available for sale as seeds. They are easy to start and grow quickly, with some varieties beginning to bloom when they are 13 to 15 weeks old. The Elite Red Hybrid can produce blooms when the plant is only 6 inches tall, according to Park Seed Company. Start your seeds indoors from January to March---use fluorescent lights 16 to 20 hours per day and keep the temperature at around 23.9 degrees C.
Growing From Cuttings
You can start more geraniums from an existing plant by taking cuttings. However, this process can be lengthy. Choose a healthy parent plant and then take 2- to 3-inch cuttings in spring or summer. Place them in vermiculite or a sterile soil mix---putting cuttings in a glass of water is not recommended because this causes the stem to rot before it roots. Use pots with drainage holes and keep them in a warm area that receives filtered sunlight.
Deficiencies Can Stunt Growth
Nutritional deficiencies also affect geranium growth rate. A lack of nitrogen will cause slow growth and stunting---it also can cause leaves to turn yellow. Too little phosphorus causes stunting and dark green leaves. A potassium deficiency will cause weak stems and stalks and death of the lower leaves. If your plant doesn't get enough calcium, its terminal buds and roots will blacken and die. To prevent any of these conditions, start your plant in soil that is rich in compost or other organic matter.