Gardening tips for March

Growing advice - Pelargoniums

Pelargoniums are often called geraniums (from the Greek word 'geranos' meaning 'crane', referring to the pointed beak on the seed). This is an incorrect, but common usage and refers to the hardy crane's bill types. For ease we will continue the usage. They are made up from about 230 species mostly originating in South Africa and Turkey, growing in mountain ranges right through to deserts. Most of the cultivars grown today have been bred from about 20 species.

The main types fit into four broad bands:

Ivy-Leafed Types

are trailing forms and grow very well in flower pouches, baskets or tubs. Their spread can be anything up to 50cm (20in) depending on the variety, but the stems can be brittle and break easily. They include single and double flowers in clusters, in reds, pinks, mauve, purple and white.

Zonal Types

are erect and bushy. They often have bicolour leaves with dark central or banded markings. The flowers include singles, semi-doubles, and doubles in clusters and the colour range includes reds, pinks, purples, oranges and white. Zonal types can be trained to form half standard (lollipop shaped) or fan shapes as well as growing well in tubs or bedding displays.

Regal Types

are quite shrubby and tend to have attractive leaves that are sometimes toothed, cut or lobed. The flowers tend to be small and single in mauves, pinks, purples and white. Ideal for tubs, borders or mass displays.

Scented Leafed Types

have been grown for their essential oil for use in the perfume industry for centuries. The scents include orange, lemon, rose, nutmeg, peppermint and eucalyptus. The flowers tend to be small and are generally pale pinks, purples, mauve or white

Some medicinal uses have been claimed over the years for pelargoniums and geraniums, as the chemical components are believed to have astringent and diuretic properties. However, the sap and leaves may occasionally aggravate skin allergies.

Some breeders have spent many years developing new and exciting varieties of pelargoniums and other plants. The first seed from the new cross is called an F1. As seed can only be taken from the first cross this tends to become rare and expensive. Here at Thompson & Morgan we try to give you, our customers, the best range of varieties to choose from and believe the best way to let everyone benefit from the hard work involved in breeding new plants is to market small quantities of Fl seed. We hope that by giving the average content of a pack will help you to pick the right plant for your planting plan. F2 seeds (seed taken from the F1's daughters) are much cheaper but don't generally have all the advantages or colour ranges of the F1s.

How to Sow for Best Results

Geranium seed is quite small, and must be handled with care. The seed can be sown from midwinter through to late spring. Sow on the surface of the compost, then cover with approximately 1.5mm (1/16 in) of Sow Lite or free draining compost. Sow Lite is a natural mineral (known as vermiculite), which when exposed to very high temperatures expands to produce a honeycomb like structure. Gardeners can benefit from this structure, as it helps to absorb excess moisture, insulates the seed and allows oxygen through the compost to the germinating seed. Then place the tray or pot in a propagator in a brightly lit place, but not in direct sunlight. If you don't have a propagator wait a few weeks before you sow and place the tray or pot inside a clean, clear plastic bag and seal with an elastic band. This will help hold in the humidity and heat required. The results may not be as good as with a propagator, as it is more difficult to maintain the critical temperature required for germination.

The compost should be moist, but definitely not wet. Wet compost (which can even be the case straight from the bag) will be cold and reduces the oxygen that the seeds need to germinate. It may even stop the seeds germinating at all. If the compost is too dry this will also cause problems. If this is the case, sprinkle a small amount of warm, clean tap water over the compost and leave it to soak in thoroughly. When the compost has absorbed the water, take a small handful and squeeze it in your fist; if water drips out it is too wet, so leave it for a short while in a well ventilated spot to dry off. If it holds together when you open your hand, it's just about right. You can now fill your seed tray or pot with the moist compost and you don't have to water it again before you sow the seed.

The soil temperature is critical for good germination. It has to be a steady 21C - 24C (70F - 75F). The temperature must not fluctuate, as this can cause poor or failed germination. Some seed will often germinate in 3 to 5 days. Some others in the pot or tray may take much longer. If this is the case, transplant the germinated seedlings and return the pot or tray back into your propagator. Remember that geranium seeds are very temperature sensitive. In a cold year or if you live in a cold area, it would be advisable to wait a few weeks before sowing. Too hot or cold soil temperatures and even a sudden drop at night may cause the seed to become dormant. If the seed has been in your propagator for three or four weeks, examine the seed carefully. If the seed is still hard, they will germinate given time, (and a steady, non-fluctuating temperature), but if they have become soft and squashy remove them from the pot or tray. Check the compost for dryness regularly. If this is the case, add a little clean water from below, being careful not to over water. Too much water can kill seedlings, as it can spread "damping off fungi" and encourage other moulds and diseases.

When the seedlings are large enough to handle, (this should be after about 3 - 6 weeks) without touching the stem, just handling the leaves, transplant them carefully into 7.5cm (3in) pots. Grow on in a cool, frost-free, well lit place, but again avoid direct sun light. To ensure really well branched plants, pinch out the growing tip after they have rooted well into their pots. Finally, pot them on into 15cm (6in) pots or baskets, (depending on the variety, or where you want them to end up) and grow them on for a few weeks in a frost-free greenhouse or similar. Gradually acclimatise them to outside conditions by placing them in a sheltered place during the day and bring them back inside at night. Watch out for cold winds as well as pets, birds, mice etc. After all risk of frost has passed they can be left out or planted into their final flowering position for you to enjoy.

Keep a eye out for greenfly, whitefly, caterpillars and other pests, if they become a problem, use a recommended proprietary brand of insecticide. Rust and Botrytis (grey mould) can, in some years, become a problem. Try to avoid watering from above and increase the ventilation. Pick off any badly affected leaves and spray with a recommended proprietary brand of fungicide. Keep the plants regularly watered and feed with a general all-purpose liquid fertiliser every 10 - 14 days. When the plants are in flower, a regular feed with a high potash feed (most tomato feeds) would also benefit them. Don't forget to deadhead and remove any damaged flowers or leaves. Deadheading will promote more flowers and help reduce the spread of any pests or disease.

Pests and Diseases

Geranium leaves can sometimes become affected by a physiological disorder called 'Oedema'. It is a corky blotch in appearance on the leaves and sometimes the stem. The cause is not understood, but it is generally attributed to a sudden increase in sap pressure caused by over watering a very dry plant.
Over-wintering