Clear Mountain Garden Treasures

Clear Mountain Garden TreasuresCulture and Germination - Giant Geranium

Giant Geranium

Family Geraniaceae
Name Geranium maderense
Common Names Giant Geranium, Giant Cranesbill

 More pictures

This evergreen aromatic biennial is the largest geranium in the world. Everything about it is large. The deeply cut snowflake shapped leaves grow from thick stems that later support the plant when the leaves die. On large plants leaves can grow to 40cm across! That in itself is showy and is worth growing this plant for.

The huge flower head appears in Spring and grows to 150cm tall and 80 cm across, with hundreds of pinky-purple flowers. A truly amazing sight.

Geranium maderense self seeds readily and is perfect for the cottage garden. It is only half-hardy and will be killed by heavy frost. It is suitable for milder areas or plant in a pot and over winter in a conservatory. When the weather warms in the Spring, bring the plant out after the last frost to flower.


Depth: Surface - do not cover as some light is necessary for germination.
When: Summer.
Where: In containers for transplanting later.
Germination is erratic and may take 1-3 months, but in some cases in less than a week. Sow thinly on a wide tray. Prick out seedlings that have 2-3 true leaves but try to leave the rest of the tray undisturbed to allow the other seeds to germinate.


Be careful when pricking out and planting as the seedlings are quite brittle. Plant the seedlings at a depth so that the potting mix is level to the first pair of leaves. Plant individually into 10cm pots or alternatively, plant into a community tray, allowing for 10cm of space between seedlings. Keep in a shady spot for a couple of weeks, then move to a lighter spot out of the direct afternoon Sun. Water well and feed moderately. Pot on to 20cm pots when the leaves are around 10cm in size.

Small Plants

If you have bought small plants, plant immediately into a 20cm pot. Keep in a shady spot for a couple of weeks, then gradually introduce the plant to more light.

The plants would have had some of their leaves trimmed to reduce transpiration. If it is quite warm, more leaves can be cut if necessary.

Planting out

Choose a site that is preferably shaded from the hottest afternoon Sun. This geranium will grow in full Sun, but partial shade is best to bring out the colour of the flowers. Allow at least 1 metre between plants and at least 1.2 metres head space.

Try to grow the seedlings in 20cm pots in similar lighting conditions to where they are to be planted. For example, if you choose to plant in full Sun, then the seedlings should have been grow in full Sun before you plant in the ground.

Water well for the first month or so to allow the plant to settle in, and thereafter, it will look after itself. Apply a 10cm layer of bark mulch to conserve soil moisture. Feed with a 6 month slow release fertilizer, such as Osmocote. Follow the manufacturer's guidelines.

Conservatory Culture

In areas with heavy frosts, it is best to grow this geranium in a 40cm pot. In the Summer and Autumn, place the pot outdoors in a spot shaded from the hot afternoon Sun. Water well and feed with a 6 month slow release fertilizer, such as Osmocote. Follow the manufacturer's guidelines.

Bring the pot into the conservatory for the Winter. Gradually reduce the water, but the mix should not be allowed to dry out completely.

Take the pot out in the Spring, after the last frost. By then, it should have started to grow the huge flower head. Either plant it into the ground or pot on to a larger pot as the flower head will make the plant top heavy.







Featured Plants
Click to view
This month: Dragon Fruit
This species of night blooming cactus... [More...]
Click to view
Last month: Furcraea longaeva
This relative of agaves produces a huge... [More...]
Random Plant
Click to view
An annual that produces masses of... [More...]