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20 August 2013

Growing Petunias from Seed

Some of the most colourful plants in my garden this summer have been the petunias, which have ranged from white via pale pink to mixed purple and white. Most have been in containers though some have been planted direct in the garden. The container ones have done better, probably due to being in a sunnier position, as sunshine is essential for petunias to look their best.

Unfortunately petunias are susceptible to wet and windy weather, though varieties have been developed which have petals which are more resistant to rain, and which open new flowers very quickly after open flowers have been damaged.

While the petunia was once a perennial plant raised from cuttings, it is now a very popular bedding plant raised from seed, though I actually bought my petunias as very small plug plants from the local nursery and grew them on.

Petunias prefer a well-drained soil and ideally an acidic one.

If you fancy growing your petunias from seed, the following tips should help:-

1) Sow your seeds from February to late April, using a peat-based seed compost which needs to be moist but not wet. You may wish to add vermiculite or sharp sand to improve drainage.

2) Sow your seeds thinly and do not cover them as they need light to break the seed's natural dormancy. Petunia seeds are almost as fine as dust, and can be difficult to handle. The best way to sow them is to carefully cut open the foil and then pour in a teaspoon of dry silver sand on top. Shake the packet to mix sand and seed, then slowly tap it to release the mixture over the surface of your compost.

3) The surface of your compost needs to remain moist or your seeds will die. To avoid this cover your trays or pots with glass or polythene to keep the moisture in.

4) You will need a temperature of between 20-27 Celsius for germination so will probably require a heated propagator. Failing this you can try keeping your germinating seeds in a warm, bright room out of direct sunlight, though you will need to keep the temperature up overnight as well. Germination should take 10 -21 days.

5) When the seedlings are large enough to handle, after about 5 - 6 weeks, transplant them into 7.5cm (3in) pots by holding the leaves. Grow on in a cool, frost free, well lit place, but again avoid direct sunlight. Pinching out the growing tip after they have rooted well into their pots should give you a well-branched plant.

6) After pricking out, temperatures below 10 Celsius will discourage growth of the main central shoot and encourage the development of side shoots from low down on the plant. This means that your first flowers will appear later.

7) Temperatures above 15 Celsius will restrict basal branching, while the main stem grows more quickly and flowering starts sooner. Although garden centres like to sell plants in flower, this does not matter to the home gardener so by sowing in early spring and keeping the temperature after pricking out cool, well branched plants should be produced which will flower more effectively when planted out.

8) When the rosettes of foliage cover the compost, you can grow the plants on in a cold frame or unheated greenhouse - just make sure that your plants are frost-free. Petunias can be planted out as soon as the last frost has gone.

9) Petunias are generally pest free but greenfly/aphids can become a problem, in which case use a recommended proprietary brand of insecticide.

10) Keep the plants regularly watered and feed with a general all-purpose fertiliser. Don't forget to deadhead and remove any damaged flowers or leaves - this will help reduce the spread of any pest or disease that may arise.

I hope you have success with your seeds and end up with a stunning display!

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