Growing Chrysanthemums in the Greenhouse

Growing Chrysanthemums in the Greenhouse

The culture of chrysanthemums, while not necessarily restricted to greenhouses in the case of early flowering types in most parts of Britain, cannot be divorced from the green-house for most mid and late-flowering types, both for cut blooms and for propagation. For all types it is culturally advantageous to produce new chrysanthemums from cuttings annually, and while a frame will suffice, a greenhouse is more accommodating.


1 Incurved – where all petals turn in to form a ball-shaped flower.

2 Incurving – where the petals of the flowers are of looser habit.

3 Reflexing – when petals turn outwards or droop.

4 Singles – with an eye and a single ring of petals. (Up to 5 rings for exhibition.)

5 Anemone flowering – which are single with a raised eye.

6 Large exhibition type – which have immense flowers and are suitable for greenhouse culture only. (Can be incurved, incurving or reflexing.)

7 Many other different types of blooms, in early, mid and late flowering groups.

Varieties are legion and change rapidly. It is therefore necessary to refer to a specialist chrysanthemum catalogue or list to keep up to date. Flower Show visitation and membership of a Chrysanthemum Society are perhaps the best ways of keeping abreast of the newest varieties and cultural techniques.

It is important to start off with good reliable stock, and thereafter maintain strict supervision to avoid stock dete-rioration due to the spread of disease by various means. The best time to select propagation stock is when the plants are in full flower, rejecting any plants which show signs of weak growth, mottled leaves, or flower distortion.


Chrysanthemums generally (other than some early varieties) are photoperiodic plants and will only initiate their flower buds when the day length is less than 14| hours. They are perennial in nature and the modern varieties have a remarkably hardy root stock (the part below ground). The flowers and foliage can stand fairly low temperatures, much depending on type and variety. Chry-santhemums will grow between spring and autumn (from May until September) out of doors, and with modern lighting and shading techniques can be induced to grow and flower under glass at any time of the year.


These centre around a well designed light admitting green-house with a heating system capable of maintaining a temperature of at least 45-50°F. For autumn and winter flowering and for propagation. A frame is desirable for hardening off, as is a slatted or capillary bench for pot grown types. There are now three main modes of greenhouse culture (excluding year-round or ‘spot’ culture, where lighting and shading is employed). These are:

1 Growing continually in pots,

2 Growing in borders out of doors for lifting into the green-house, 3 Direct planting in greenhouse borders.

There is of course also outside culture of chrysanthemums, when the plants, although they may be greenhouse raised, will flower out of doors.


Times of propagation are as follows:

1 Large exhibition greenhouse varieties in December and January.

2 Late flowering and mid-season varieties in February and March.

3 Early flowering types in March and April. Propagation material should be selected from stools overwintered in protected frames or frost free greenhouses. Short growths are selected which are | in. in diameter and 2-3 in. long. The cuttings should preferably be taken below a joint, but this is not essential, and the lower leaves are always removed. After dipping the cuttings in hormone powder, insert them | to J in. deep in seed trays at a distance of 1-1 ½ in. apart, using a rooting medium of equal parts finely riddled peat and sand, or, for later propagation, John Innes Seed Compost. The cuttings should be well watered in and given a temperature of 55-60°F. Rooting generally takes place in 14 to 30 days, according to variety, with an average of 21 days, although on mist propagation benches rooting can be achieved very much quicker. Polythene bags placed over the top of the boxes will create humidity and hasten rooting. Cuttings may wilt for the first few days, but shading with newspaper will help to prevent this. An alternative to box rooting is rooting directly into peat pellets, the cuttings being inserted individually, and there is much virtue in this method.


Cuttings, when rooted, as can be seen by freshening tip growth, can either be potted into 3 in. pots of clay, plastic or peat, filled with a good potting compost, generally John Innes Potting No. 1, or alternatively later taken cuttings can be planted out 5 x 5 in. apart in good rich soil in a cold frame. Pot firmly and carefully, giving the plants plenty of light and keep them merely moist to induce hard growth.


The practice of stopping or pinching is carried out with all but the Spray types. This is done by removing the top of the single stems completely, avoiding bruising of tissue, and is carried out when 6 to 9 in. of growth has developed and buds are seen to be breaking. It results in the formation of side shoots. It is important not to stop a plant simultaneously with potting or planting out, and with pot grown types it is generally carried out after either the second potting accord-ing to growth rate, while with outside planted types, it takes place after they have recovered from the shock of planting, generally around the first week of June. The number of stems allowed to remain often depends on purpose.


Plants intended for outdoor culture, or ‘lifters’, should be placed in a cold frame and hardened off ready for planting outside in early or mid-May. Planting distances for cut flower production are 12 x 14 in. apart in a 3 to 4 ft. wide bed. Earlies for dwarf bedding culture can be planted a little closer, around 12 x 12 in. For’lifters’a little more space may be given, up to 18 in. apart. Support must be given, either with individual canes or netting strained to posts. Early dwarf types require no support.


Plants in 3-in. Pots are moved on to 5-in. Pots, checking that the roots are well through the ball by careful inspection. This is done by holding the pot upside down and allowing the root ball to drop into the hand. Use John Innes No. 2 compost and crock clay pots, putting plenty of roughage in the bottom of the pot. Pot all plants firmly.


The final potting is into 8- or 9-in. Pots, using plenty of roughage and John Innes No. 3 compost. Plants must be potted very firmly, using, if necessary, a potting stick. Three strong 4 to 5 ft. canes are then inserted around the edge of the pot and the plants are supported by strong twine around the canes, later of course tying the number of stems allowed to form individually to each cane. Place pots in a square for a few days to give natural protection and then put them in a line, keeping the pots 6 in. apart, or on outside beds or gravel paths not recently treated with weedkiller. Keep them entirely level and tie at least one cane in each pot to a strong fence erected with posts and wires. Plants should be fed and watered regularly, and pots given a twist occasionally to prevent rooting into base.


Disbudding should be carried out regularly (except for Spray varieties) leaving the centre or terminal bud in each case, unless specific recommendations are given to the contrary with any variety.


Plants are generally lifted into the greenhouse in September or early October before any heavy frosts occur. The green-house is kept fully ventilated for a few weeks no heat being necessary at this stage, and thereafter heat is given at the 45-50°F. Level. Watering and feeding is continued, particular attention also being paid to pest and disease control, especi-ally mildew, which can be largely prevented by adequate ventilation.


Before lifting plants in, greenhouse borders are forked over, but do not generally require much more attention, especially if a crop of tomatoes has been grown. Generally, however, 4 to 6 oz. Per sq. yd. Of a good general fertiliser should be applied. The pH of the soil should also be adjusted to 6.5. Plants are lifted with a sharp spade, it sometimes being ad-visable to cut around the roots a fortnight or a week before. They are lifted with as large a root ball as possible, placed in the greenhouse border fairly tightly, and thoroughly watered in. Some wilting may occur, but if the greenhouse is kept cool the plants quickly recover. Some varieties will, of course, lift better than others. Heat is given after a couple of weeks at the 45-50°F. Level.


Widely practiced by commercial growers, this system avoids a great deal of the summer attention required out of doors. Nevertheless, it also restricts the use of greenhouse borders for tomatoes (other than for a very early crop) and other crops. Under greenhouse conditions chrysanthemums usually grow much more quickly than they do out of doors, and the growing season can therefore be considerably shortened. Planting may take place from June to mid-August with natural illumination. The problem, however, is that while it is simple for the commercial grower to obtain rooted cuttings in quantity for direct planting from specialist raisers, it is difficult for the amateur to obtain merely a few plants. It may of course be possible to get a few cuttings from a commercial grower if these are ordered early enough. Alternatively cuttings are taken early in the year, when available, and planted in the greenhouse border at a distance of 9 x 9 in. apart. These are then stopped when they are growing vigorously by pinching out the tops, and in due course cuttings are taken again and rooted. These provide the young plants for setting out in a well-prepared greenhouse border which has been dressed with lime to give a pH of 6.5, and a compound fertiliser at 6 to 8 oz. Per sq. yd.


If planting between June and early July from self-raised or bought plants, allow 10 x 10 in. or 9 x 9 in., if mid to late July allow 7×8 in., and for planting up to around the third week of August, allow 5 x 5 in. and take only one stem (without stopping). It helps to give even growth if plants are ‘graded’ into sizes when planting. Beds should be approxi-mately 4 ft. 6 in. to 5 ft. wide.


Plants generally make rapid growth under warm greenhouse conditions, and stopping is carried out a week or so after planting for all but the single stem crop. Regular watering is essential, as also is liquid feeding, the emphasis being on potash or nitrogen, according to whether growth is soft or hard respectively. Support is best achieved by means of 6 in. mesh netting of either hessian or plastic strained on supports, and this is gradually raised as the plants grow. Stringent pest and disease control is essential, and adequate ventilation should be given constantly, maintaining temperatures in the 55-60°F. Region, especially during bud formation time around September and October.

Flowering period will extend from October until Xmas, or later according to variety, this depending on what is called the response group. This is a technique invaluable for the cut flower enthusiast, but it will be found that a little practical experience is worth a great deal. Both standard and spray varieties can of course be grown. Apart from cut flowers, pots of dwarf spray chrysanths can be grown on the same principle, 3 to 5 plants per 6-in. Plastic half-pot, following much the same timing.


Based on the principle that certain chrysanths only form their flower buds when the daylight is less than 144- hours, this is also a technique which is widely practised commercially. Both bed and pot culture can be practised, in the first case in 5 ft. wide beds, in the same manner as described for direct planting, and for pot culture on either open or capillary type benches, usually 5 young plants being planted per 6-9 in. ‘half-pot’ or seed pan. The border soil must be of good quality and regularly changed or steam sterilised, not only to avoid disease but to reduce build-up of chemicals or plant toxins. This can in fact create cultural difficulties for the amateur, as chemical sterilisation is not often feasible for a number of reasons. With pots John Innes No. 2 or U/C Summer Mix should always be used. Temperature must be accurately controlled in the region of 55-60° F. if growth is to be maintained. Facilities must also be available for a line of 60 watt tungsten filament lights centrally situated over the beds at a height of 5 ft., (4 ft. apart) and also a framework of wires for supporting black polythene shading, so that by either lighting or shading the plants the photoperiodic impulse can be adjusted according to the time of year to either induce the plant to develop vegetatively (by simulating a day length of more than 14| hours) and initiating flower buds by bringing it below 144 hours by shading.

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