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Raising Begonia from Seed
by Peter Sharp

Propagation is the aspect of growing begonias which I most enjoy. Certainly watching over precious plants as they mature, agonizing as to whether they will flower, finally enjoying the beauty of the blooms and the endless variety of the foliage as well as savoring a garden or a shade house full of begonias, all give me that thrill which only a true begoniac can know. However, producing new life from cuttings or seeds is something really special.

I am fortunate enough to be a horticultural volunteer at the Royal Botanic Gardens here in Sydney, Australia and have been such for the past 15 years, my particular input being, quite naturally, the care of an extensive begonia collection. We grow them mainly in the open garden and have some two thousand plants out of doors all year round. Enlarging the collection is now my present priority as we have been asked to plant another very large garden with begonias, and seed is the primary source of new species for this daunting task. So I have perforce become somewhat adept at raising begonia from seed.

Mickey Meyer, a very well known and much admired begonia grower, now sadly departed, told me many years ago that her secret for raising from seed was to use the same mix for the seeds as she used for pricking out and eventual potting, and I have followed this advice with excellent results. She explained that using the same mix ensured that the seedlings would not suffer much set-back when moved. How ever, I think it wise to omit any fertilizer from this first mix to avoid putting the seedlings under any stress when they first emerge.

The first and perhaps the most important aspect of raising from seed is to ensure that conditions are as sterile as you can make them, for ‘damping off' (a fungal disease) is your very worst enemy. There are several ways to sterilize the mix: microwaving for a few minutes, pouring boiling water through it, or simply leaving a flattened plastic bag of it in the hot midday sun, will all suffice.

Two further points before we start. Firstly, begonia seed is as fine as finely ground pepper, so work away from breezes, fans and sneezes, and open the packet with extreme care. Secondly, begonia seed needs HEAT, LIGHT and MOISTURE in order to germinate, so neither cover the seed with mix nor the container with other than a cover which allows light to penetrate.

Let’s sow some seed:

1. Fill a suitable container (I use 4” square squat pots) with sterile potting mix, removing any large matter (such as bark pieces, pebbles, etc.) from the surface, and leaving a clear half inch below the rim. Tamp it down lightly.

2. Water the mix in the container with clean water. If your water source is suspect, then it too may need sterilizing. Cover with plastic or glass and allow to stand overnight to drain. The water remaining in the mix after draining must last until germination occurs as watering during the germination period is not recommended, BUT the surface of the mix must not be allowed to dry out during this period. Bottom watering should be used if watering does become necessary, being careful not to flood the surface of the mix.

3. Next day sow the seed, scattering it evenly and not too thickly over the surface of the mix (a small pinch will contain upwards of 50 seeds!). You will doubtless work out your own way of doing this. One method is to shake the seed gently from a sheet of paper suitably creased (practice a bit by trying to sow seed onto an other sheet of paper until you obtain an even distribution). Now, cover the container with glass or plastic. I prefer a suitable piece of clear plastic film secured with a rubber band so that a good seal results.

4. Seeds need heat of between 70° and 75° F (21° to 25°C) to germinate, so if you have no source of bottom heat it is best to wait till the weather is hot enough before seed sowing. If you have a heat pad, then stand the container on this in a position where it will receive good light but not direct sunlight. Bottom heat is often readily available in the home - the top of the refrigerator or the top of a floor level hot water heater for instance. Test for heat level before using! You will note that water condenses on the plastic cover; simply tilt the container to allow this water to run free.

5. Germination will occur in a surprisingly short time with fresh seed, anywhere between 10 and 14 days, but this may take longer. Some seed can take up to two months before coming good, so be patient! The first indication is a slight green bloom on the surface of the mix, but the small seed lings will soon look more like real plants!

6. It’s about here that I disagree with the experts! They tell us to gradually lift the cover from the pot over a period of a week or more, commencing some 10 days after germination, their reason being ‘to harden off the seedlings’. I maintain that begonias are tough plants and I have had no problems with lifting the covers completely about a week or 10 days after germination I then take the pots off bottom heat onto my growing benches. HOWEVER, this should not be done if local overnight temperatures are likely to drop below about 50°F (10°C). Do not leave the uncovered containers on bottom heat as the mix will very quickly dry out, more quickly than you think, and you will lose your seedlings! Once again, wait till warm weather before seed sowing, unless of course you are fortunate enough to have a heated greenhouse.

7. At this stage I also commence feeding the seedlings, using a good water soluble fertilizer in a hand mister. Not much at first, but gradually increasing both the amount and frequency, and again contrary to the experts, I mix the fertilizer according to manufacturer’s recommendation, not the half or quarter strength the experts often say!

8. The seedlings will stay the same for a week or two while the root systems develop, and then they will suddenly start to grow, and when this happens they will very soon put out their first true leaves. This is the stage of growth when it is necessary to prick out the seedlings into their next container. Certainly they are still very small plants, but that’s the thing to do so don’t be worried!

9. These small seedlings need company in their next container, so don’t be tempted to plant them singly in small pots—they will more than likely die. Plant them no more than one inch apart in a suitable container. Usually you will have a lot of seedlings, so find a seedling tray (we call them nursery ‘flats’), fill it with mix which this time contains a ration of controlled release fertilizer, dibble holes an inch apart, and gently move the seedlings from their seed bed. It takes a little practice to untangle them if you sowed too many seeds! It is beneficial to plant them a little deeper in these trays than they were in the seed trays. Weekly fertilizing with a nitrogen rich fertilizer is now required. In no time at all your seedlings will be ready for potting up.

Now that wasn’t so very hard, was it? And you have perhaps discovered a new aspect to begonia growing, and a fascinating way to increase your collection of species.

Peter’s growing collection includes the following species grown from seeds:

B. barkeri, B. carolineifolia, B. chivatoa, B. fusca, B. heracleifolia, B. mariti, B. nelumbiifolia, B. sericoneura, & B. wallichiana.

Peter Sharp lives in New South Wales, Australia
Further reading: Growing Begonias  by Peter Sharp. Kangaroo Press NSW 1998


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