First published in
Propagation of the Primrose & Polyanthus from Seed
It is often said that the seed of the Primrose and Polyanthus should be
sown whilst it is fresh, that is within twelve months of gathering. This
however is not entirely true, for seed can be stored satisfactorily for at
least three years without any noticeable deterioration in the germination rate
or the quality of the subsequent plants. Seed must however be stored correctly,
the best way being to place the seed in an airtight container and either place
the container in a cool place, or better still in a refrigerator.
Polyanthus seed can be sown at almost any time of the year with the exception of June. There are three recognised sowing periods, namely July to September, December to February; and March to May. Despite the fact that in nature seed is sown in July to September I have found that the best results occur from an early Spring sowing. However I have also had no problems, or difficulties, with seed sown at other periods. In fact the Primrose & Polyanthus is a very easy plant to raise from seed, and seems to tolerate both adverse conditions and mismanagement.
From a sowing of fresh seed - that is a July, August and September sowing - a percentage of seeds will not germinate until the following spring; this percentage seems to vary according to strains, and colours. From a sowing at this time seedlings must be given protection through the winter and a minimum temperature of minus 5ºC must be maintained. The important factor under such conditions is to ensure that should the temperature fall below freezing that a slow thaw to allowed. Any attempt to thaw the soil or seedlings will result in disaster. A sowing between December and February follows the natural sequence of germination. The best method is to place the seed trays out of doors in a position protected from rain, or dripping water - a Hessian sacking canopy is ideal. This sowing also can be carried out directly into a frame, though this is the method used in commerce I cannot see any sound reason for it's preference to the use of seed boxes.
Sowings during March, April and May are identical to that between December and February with the exception that great care must be taken to protect the seed trays from direct sunlight or from drying out. The great advantage of a December to February Sowing is that the seedlings have a full twelve months vegetative growth before flowering, a later sowing reduces this period of growth, and an earlier sowing often results in plants flowing only months after sowing, thus producing inferior flowers, and adversely affecting the plant size.
Many seed catalogues and articles in amateur papers state that seed is best germinated at a temperature of I5-16ºC, and advocate the use of propagators. Not only is this an unnecessary expense, but if the temperature is too high it can seriously affect germination. It is important to remember that the Primrose and Polyanthus are hardy plants, and should be treated as such. The best results are obtained by following the natural sequence, or reproducing them as accurately as possible. For fast and full germination cool moist conditions are required.
Because seed is small & round, and liable to roll into depressions the surface of the compost on which the seeds are to be sown must be smooth and firm - any large pores will result in the seeds being buried. The seed should be sown thinly, evenly and MUST not be covered with compost. Great care must be taken when sowing the seed, due to the spherical shape of the seed they are prone to roll and bounce about, and this can result in seed collecting in pockets. Some success can be achieved by applying a very light dressing of fine chippings to the surface before sowing the seed.
To promote faster and even germination some growers advocate watering the seed in with water at a temperature of 49ºC, and repeating the treatment for two further days using water at a temperature of 45ºC. This treatment should not be used on Winter sowings, when freezing may destroy the germinating seed. In the Summer a treatment of water at 45ºC should be given on one day only. This treatment sounds at first to be somewhat drastic, but is highly effective.
It is essential that the compost and seed is never allowed to dry out and accordingly the trays should be checked regularity. Watering must be done with care, on a large scale a very fine rose must be resorted to, but even with this there is a great risk of washing the seed into a corner. Where the seed is sown in trays the best method is to stand the trays in shallow water so that the compost is moistened from beneath, and there is no risk of swamping the seed or tiny seedlings. Whilst it is important to ensure that the compost is kept moist, it is also imperative to ensure that there is adequate drainage, and that the compost does not become water logged.
Once the seed is showing distinct signs of germination it should be lightly covered with compost or vermiculite to minimize the risk of drying out. Care must be taken however that the seed is not buried, and a very fine sieve should be used.
The sowing medium for Primroses and Polyanthus has been a subject of debate over the past few years, and at the present time some growers advocate the use of a loamless compost such as Vermipeat, though peat and sand based loamless composts are not recommended. Growers who recommend loamless mediums in preference to loam based composts do so because of the variability of loam.
Loamless advocates have little worry with 'damping off', however provided seedlings in a loam compost are given adequate ventilation and the seed sown thinly there is only a slight risk, especially if the loam has been correctly sterilized. Should any sign of damping off become visible an immediate treatment with Cheshunt Compound, Captan, or Benlate will prove effective. As a precautionary measure freshly sown seed can be watered with liquid Copper Fungicide at a rate of one fluid ounce per five gallons of water.
Seedlings should be transplanted at about the first true leaf stage, to leave longer may result in starved or drawn seedlings. Undoubtedly the best results are obtained by transplanting into boxes at a spacing of 5cm, into Jiffy pots, or best of all into plug trays. Under these condition the young plants can be protected from the elements, and their every need satisfied. In trays the young plants make rapid headway and can be planted out into their flowering position as well developed plants. Undoubtedly these plants will produce the best flowers. On a large scale however, not only is this an expensive method in terms of labour, time and space, but also quite impractical. Under these economic restraints seedlings are planted out directly into open ground at a spacing of 20 cm. Initially the seedlings will look lost, but once growth is well developed there will be little or no soil showing between the plants.
An alternative method is to space the seedlings 10cm and when the leaves touch every other row, and alternate plants in the remaining rows are removed and planted in another flowering bed, thus giving a 20cm final spacing. This later method reduces the amount of weeding whilst the seedlings are small, and it always seems that at a wide spacing the seedlings are slower in growth. On an economic reasoning this method makes sense for only half the amount of land is planted with unproductive seedlings, thus allowing a crop to be grown on the other final flowering bed. Where cloches are used it is important to space the plants so that the rows are at a suitable distance for covering with the maximum effect, and without the necessity of moving rows which lie between cloche placements.
© John S Harrison, 1976
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