Monday, August 06, 2007

Begonias galore

It is a general rule of gardening that we start out liking very colourful flowers, but as we age and gain horticultural experience, our taste becomes more refined. We lose our enthusiasm for the bright baubles of the garden, and our minds turn to more sophisticated plants – hellebores, snowdrops, ferns and natives species of all kinds.
That has happened to me, but only to a degree. I do like hellebores, and have a few snowdrops too. This weekend I have planted a dozen ferns and my taste in roses and the like is to the more subdued colours.
But when it comes to tuberous begonias, all my learned experience goes out the window, and I want the brightest and biggest flowers I can find.
A passion for these colourful potted plants is not something I would have predicted, but when we were running the nursery, we grew thousands of these for the potted plant market and I became converted. Ever since, I have grown a good number of each year.
August is the time to get started on the new blooming season, with new plants to be bought and old plants to be re-started into growth.
Many growers recommend starting the new tubers into growth in growing trays, by placing them on a good free-draining potting mix, covering with about 15 mm of mix. The soil is then thoroughly soaked once, and once only, then the tubers are left to sprout. Do not water again as the tuber has not made any roots and cannot take any water up, and could rot.
As the plant begins to sprout it can be carefully removed from the mix and potted up, with care taken to ensure that the pot is the right size for the tuber.
I used to start my tubers this way, but I have found results are just as good if the plants are started in the pot that they are to be growing in, and it cuts out one step in the process. It is still important to make sure the soil does not become waterlogged as the tubers will not tolerate that.
I fill the pots to about 15 mm from the lip, using a good quality potting mix with slow release fertilizer. I place the tubers about three quarters into the soil, leaving the top of the tuber- the flat side- slightly above the surface. This is important as the plants are susceptible to stem rot, which can cause the branches to rot at the tuber, and can infect the tuber.
I ensure that the older, and larger, tubers are placed into larger pots. It will become important as the plants grow for two reasons. They will need a lot of food as they grow, and they will also need the support and balance a larger pot affords.
I water all my tubers in well, and then leave them in the glasshouse to sprout. If you do not have a glasshouse, any warm sheltered spot will do.
Once the plants have started growing I try to remember to put stakes in place, as, if I forget to do it at this stage, I will not do it until the plants are starting to fall about and then I will have more trouble putting the stakes into the soil without damaging the plants. Begonias have very brittle stems and they are very easily damaged. Later in the season, when they are laden with flowers, they can be very easily snapped.
I do not normally grow hanging varieties, but if you do, it is important to pinch them out when they are young. Once the growing tip is about 50 mm long pinch out the principal growing tip. This will encourage the plant to branch out at the base, giving a better effect as it grows.
Once the plants are well established I like to place them on our patio, where they are protected from the worst of the sun and heat, and where we can control the watering. It is important that they are not allowed to dry out but it is equally critical that they are not left drowned in their pots. Good air movement is important too, as they are a little prone to mildew and if grown in too sheltered an area they will quickly become disfigured. One wet and muggy year we had a dreadful problem with mildew, losing some tubers so we are vigilant against it. At the first sign of any infection, apply a fungicide. Prevention is the better option though, so make sure your plants are not too crowded and have good air circulation.
In the autumn, when the flowers have done their thing, I simply place the pots back in the glasshouse, on their side, so they can dry off and mature. It is those pots I will be cleaning out next weekend.

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