Planting Flower Bulbs for the Greenhouse


Planting Flower Bulbs for the Greenhouse

A cool greenhouse, with a minimum temperature of, say, 7° to 10° C. (45° to 50° F.), is the passport to a whole world of delight with flower bulbs, corms and tubers. Many of those which are hardy garden plants are also splendid for growing in an entirely unheated greenhouse where, grown well and protected from the weather, they reach a perfection rarely possible to attain under garden conditions. Many of the flowering bulb plants mentioned are sometimes described as garden plants while others are only suitable for growing under greenhouse conditions. Perhaps one of the most important things to remember when growing and planting flower bulbs under glass is that slow, steady growing conditions will produce the sturdy, fine-flowered plants which can be grown.

Some can be forced, like the daffodils, hyacinths, freesias and early tulips, while others, like gladioli, are not suited to this treatment. To get the correct growing rhythm, therefore, one should aim to plant the bulbs, corms or tubers at the correct time. Most start off plunged in cold frames or under a covering of ashes outdoors, only being introduced to the greenhouse when growth is well under way.

Brief cultural instructions are given for each genus in the notes which follow.

Achimenes 'Yellow Beauty' Achimenes. The achimenes in shades of purple, blue, red and white are becoming increasingly popular both for pot cultivation and for use in hanging baskets. The tubers can be started into growth at any time between February and late May for summer and autumn flowering but, of course, as they need a temperature of around 16° C. (60°F.) the earlier one starts the plants into growth the more heat has to be provided.

The John Innes No. 1 Potting Compost suits them well and the tubers are best started into growth in boxes, these being covered with about 1 in. of compost. When growth is well under way move them into flowering-size pots (5 in. or larger) or baskets. When using them for hanging baskets I like to plant them up the side and to have a fair number on top. Water with especial care at first but more freely when the plants are in full growth. When flowering has finished and the foliage has died down stop watering altogether and store the tubers in a frost-proof place until it is time to start them into growth again. Increase from seed, leaf cuttings, ordinary cuttings or scales rubbed off the tubers and sown like seed. The seed itself needs a high temperature for germination and the seedlings will bloom in the second year.

African,Corn Lily, see Ixia

Amaryllis Amaryllis. The rosy-red Amaryllis belladonna with its striking lily-like flowers is an excellent plant for a greenhouse with a minimum temperature of 7° C. (45° F.). pot the bulbs singly ‘n 6 in. pots just below the surface in August using the John Innes No. 1 Potting Compost. Water sparingly until growth is well under way and then increase the amount given. Do not water at all during the resting period in early and midsummer.

Arum Lily, see Zantedeschia

Babiana stricta Babiana. Attractive plants with funnel-shaped flowers on 6 in. stems, the babianas are available in such colours as blue, pink, red and cream. pot the bulbs 3 in. deep in sandy compost in October or early November putting four or five in a 4 in. pot, plunge in a cold frame and move to the cool greenhouse when growth begins. Ripen off the bulbs after flowering and store till planting time comes round again. Increase by seeds.

Begonias (tuberous) Begonias (tuberous). It is not surprising that the tuberous double and pendulous begonias-the latter are superb for hanging baskets-are so highly regarded by gardeners. They have outstanding decorative value. March is a good month to start the tubers into growth and the plants will then begin to flower in late June, but February or April planting is quite suitable if for some reason that is preferable. Press the tubers, hollow side uppermost, into boxes of moist peat and coarse sand. Shade from strong sunshine and provide a minimum temperature of 13°C. (55°F.). Water with care and as soon as growth begins pot into 3 in. pots filled with John Innes No. 2 Potting Compost. Re-pot the plants into 5 in. or 6 in. pots when they have made a few inches of growth. Shade and moist atmospheric conditions are essential for success, for if they are lacking there will be trouble from bud dropping. Be especially careful when watering after Potting as the plants are at their most vulnerable during the period when they are re-establishing themselves in the new compost. Only water the plants when the compost is becoming dry, and then water thoroughly.

When the flowers develop it will be noticed that single female flowers develop on both sides of each male double flower, and the female flowers should be removed. Provide the flower stems with support as they develop. Continue watering after flowering has ceased until the foliage starts to turn yellow and then dry the plants off by gradually reducing the amount of water given. When the compost is quite dry, store the tubers in the greenhouse, under the bench or in some other frost-proof place, until the time comes round again to start them into growth.

They can be propagated from seed sown in January or February in John Innes Seed Compost and a temperature of 18° C. (65°F.) or rather more. For anyone with a small greenhouse, though, I would recommend buying say a dozen tubers and dividing these up in the second year. There must be at least one or two shoots on each piece, or division, and they should be dusted with flowers of sulphur before potting.

Blood Flower, see Haemanthus

Cape Cowslip, see Lachenalia

Clivia Miniata Clivia. An especially colourful spring- and early summer-flowering greenhouse plant is the clivia. Hybrids of Clivia miniata are available in various shades of yellow, orange and red. This plant is easily recognised, for the bold flower-heads on strong stems are carried above deep green, strap-shaped evergreen leaves. pot the fleshy roots in February in the John limes No. 1 Potting Compost in 5- to 10 in. pots according to the size of the roots and place the pots in a sunny part of the greenhouse. A temperature of about 13° C. (55°F.) is suitable. Water the plants generously throughout the growing period which lasts until September. Feed with liquid manure and shade against strong sunshine. From September until spring water must be applied sparingly – just enough to avoid drying out, and the temperature during this period must be not less than 7°C. (45° F.). Increase the water supply when the plants start flowering in the spring. The important thing to remember with clivias is that they will only flower well when so pot-bound that they almost burst their pots.

Clivias are increased by seed sown in a heated greenhouse or by dividing the roots at the time of re-potting.

Crocosmia Crocosmia. Crocosmia aurea, which bears long spikes of orange-red flowers in summer, is a first-class plant for the unheated greenhouse. To make a good display plant five corms in a 5 in. pot in October and use a mixture of equal parts loam, leafmould and sand. Plunge in a cold frame and move to the greenhouse when growth begins. Increase by offsets or seed.

Crocus Crocus. These are very attractive as pot plants. October is the best time for Potting, using a sandy compost; place four corms in a 3 in. pot and cover to a depth of 1/2 in. Plunge under ashes outdoors until growth begins and then move to the greenhouse. The plants can be forced by giving them a temperature of 13° to 16° C. (55° to 60°F.) in December. Do not use them as pot plants for a second year. After flowering, store these corms until planting time comes round again, when they can be planted out in the garden. Increase. By offsets or seed.

Cyclamen Cyclamen. The greenhouse cyclamen, strains of Cyclamen persicum, are available in lovely shades of red, pink, salmon and white. They are among the finest greenhouse plants for autumn and winter decoration. So far as I am concerned, they are Number One.

Cyclamen must have a minimum winter temperature of 10° C. (50° F.). I sow seeds in late May or early June to produce plants that will flower in 18 months time. I have tried sowing in January and hurrying the plants along to flower in the autumn of the same year, but it does not work-the plants tend to flop when they are brought into the house for they do not have the necessary sturdiness. Also, of course, it is not easy to provide the high temperature required when sowing at that time of year.

Sow the seed in pans or boxes filled with John limes Seed Compost, spacing them out evenly on the surface. Cover with sifted compost and firm, and then cover the container with glass and newspaper until germination takes place, wiping the condensation from the glass daily. When the seed germinates place the container in a shaded garden frame out of the way of draughts. Water with great care, and as soon as the seedlings can be handled move them into boxes or 2-½ in. pots filled with John Innes No. 1 Potting Compost. Firm Potting at all stages is essential. Keep growing steadily in a temperature of 13° to 16° C. (55° to 60° F.) with shade from direct sunshine and move into 4 in. pots when the present pots are full of roots. Always pot so that the top of the corm is at surface level. I always like to add a little dry cow manure to the compost used for cyclamen-when I can get it-and a little extra general fertiliser. I have also found that cyclamen appreciate a little riddled sphagnum moss in the Potting mixture.

In autumn the plants are brought back into the greenhouse and kept growing steadily. By June of the following year they are ready for Potting into the 5 or 6 in. pots in which they will flower and they should be hardened off carefully and placed in a shaded cold frame for the summer. Then, in late September, they are brought back into the greenhouse where they flower in autumn and winter. The earliest flowers to form are best removed, I find, and I then get excellent blooms from about mid-October right through to March.

The hardy cyclamen C. repandum can be used as a pan plant to decorate the unheated greenhouse. pot in a mixture of equal parts loamy leaf-mould and sand and plunge in a cold frame until growth begins. Then bring the plants into the greenhouse.

Daffodils see Different Types of Daffodils

Flower of the West Wind, see Zephyranthes

Freesia Freesia. The hybrids of Freesia refracta include many delightful rather soft colours and make splendid plants for the greenhouse which has a temperature of not less than 4° C. (40° F.). Their fragrance is also a great attraction. I prefer to grow my plants from seed rather than corms, and they can be obtained as separate or mixed colours. I sow the seed in March in pans containing a light, sandy compost and provide a temperature of 16°C. (60°F.). When the seedlings are about 1 to 2 in. tall prick them out 2 to 3 in. apart into really deep boxes – they have long tap roots – and keep these in the greenhouse until about mid-June when they should be stood beside the greenhouse wall outdoors in shade. Keep them well watered and bring them indoors again in September. The plants need support, as they grow nearly 2 ft. tall so place twiggy sticks between them so that they can grow up through them. The plants will start flowering in October and will continue until February-March.

When growing from corms, place five or six in a 5 in. pot in John Innes No. 1 Potting Compost in August for flowering in January, and in subsequent months up to November for later flowering. Bury them 1 in. deep. Put them in a cold frame and just cover with straw or leaves. When growth starts bring them into the greenhouse and place on a shelf near the glass. Introduce them to heat gradually. These plants, too, have to be supported with sticks and secured with raffia or twine.

Galanthus (Snowdrop) Galanthus (Snowdrop). There is something particularly appealing about a pot or pan of snowdrops. These plants will grow well in a mixture of 2 parts loamy soil and 1 part each of leafmould and sand. Either medium-sized pots or pans are suitable and the bulbs should be set 1 in. under the surface. Plunge in a cold frame until growth starts, then bring into the greenhouse.

Gladiolus Gladiolus. The gladioli make good greenhouse plants and the dwarf colvillei can be forced-but only very slightly. Do not attempt to force the large-flowered gladioli. Give all gladioli a rich, loamy, well-drained soil. pot in January or February placing one corm only of a large-flowered gladiolus in a 6 in. pot 1 in. deep. Move to a cold frame and cover the pots with straw or similar protective material during severe weather. When the flower spikes appear move plants into a cool greenhouse. Three plants of the colvillei type of gladiolus can be grown in a 6 in. pot at the same depth and grown on in the same way as the large-flowered type. After the flowers have gone over give decreasing amounts of water until the foliage withers. Clean the corms and store in trays or boxes in an airy, frost-proof room or shed.

Gloriosa (Glory Lily) Gloriosa (Glory Lily). The gloriosas are tuberous-rooted climbing plants needing warm greenhouse treatment. Those usually grown are Gloriosa rothschildiana with red and yellow flowers, and G. superba with orange and red flowers. Both bloom in summer. I start my plants into growth in early March, using a compost of equal parts loam, peat, leafmould and sand. The temperature needed is 21° C. (70° F.) and water is not given in any quantity until growth is well under way. The growths are trained up wires on the greenhouse wall. When flowering has finished in autumn the plants are dried off and the roots left in the pots until early March when they are repotted and brought back into growth. Increase from seeds, and offsets which have to be taken away from the parent bulbs with great care when they start into growth in the spring.

Glory Flower, see Gloriosa

Gloxinia Gloxinia. The summer-flowering gloxinias in their gay colourings of red, pink, blue and white are splendid greenhouse plants which present few difficulties in cultivation although not every greenhouse owner can raise them from seed as they require a germinating temperature of 16° to 18° C. (60° to 65° F.) to be maintained in January or February. An easier way is to grow our plants from tubers which can be started into growth in March or April. These still need a temperature of 16° C. (60° F.) but this is more easily achieved in the spring months. Plant the tubers in boxes containing John Innes No. 1 Potting Compost or a mixture of leafmould and peat with a little compost, cow manure and sand added. The crowns of the tubers should be just above soil level. Place the box or boxes in a shaded, warm part of the greenhouse and just keep the tubers slightly moist. Also keep the atmosphere moist by overhead spraying. When the tubers have made about 2 in. of growth move them into 5 or 6 in. pots filled with John Innes No. 2 Potting Compost. From now onwards plentiful supplies of water will be needed and the plants will probably want Potting on later to 7 or 8 in. pots. During the later stages of growth a temperature of 10° to 13°C. (50° to 55°F.) is needed with plenty of ventilation.

If the plants are raised from seed a temperature of 16° to 18° C. (60° to 65° F.) is needed as already stated and I prefer early February to January sowing because it saves considerably on the heating costs. The seed, which is very fine, is sown on top of pots filled with John Innes Seed Compost. The pots are then stood in a propagating case until the seed germinates. Prick the seedlings out as soon as they can be handled into boxes filled with John Innes No. 1 Potting Compost. They need warmth and shade from sunshine and will soon be ready for a further move into 3-½ in. pots filled with the same compost mixture. When ready, move them on again into 5 or 6 in. pots for flowering in July. They will then be in flower until September or October. Liquid feeding at intervals of about 10 days during the growing period will produce finer plants than otherwise.

Give decreasing amounts of water after flowering and allow them to ripen off their growth in a cold frame. Then, in the autumn, dry the tubers off completely and store over winter in a room with a minimum temperature of 10° C. (50° F.) and a dry atmosphere.

It is possible also to raise plants from leaf cuttings during the summer.

Grape Hyacinth, see Muscari

Guernsey Lily, see Nerine

Haemanthus (Blood Flower) Haemanthus (Blood Flower). The haemanthus are striking greenhouse plants which present no difficulties in cultivation. Those most often grown are multiflorus and katherinae, both of which bear red flowers in spring. These flowers are distinctive, being carried in ball-like heads on strong stems. The autumn-flowering H. albiflos has a quite different appearance with flat-topped heads of white flowers. All are about 1ft. tall and make big plants.

The spring-flowering species should be potted between August and November and the autumn-flowering one in March and April. Good drainage is essential and I find a mixture of loam and sandy peat very satisfactory as a growing medium. Use pots only slightly larger than the size of the bulbs and cover the bulbs over completely with compost when Potting. Place in a sunny part of the greenhouse and provide a minimum temperature of 16° C. (60° F.) between April and September and 10° C. (50° F.) from then until March, preferably 13° to 16°C. (55° to 60° F.). When flowering ceases reduce the supplies of water and stop watering altogether when the foliage starts to turn yellow. Rest the bulbs until it is time to restart them into growth for the next season. Re-potting is only necessary once every three years or so. Increase from offsets.

Hippeastrum (Amaryllis) Hippeastrum (Amaryllis). The hippeastrums, often listed under the name Amaryllis, are superb for the greenhouse for spring and early summer, and with the provision of extra heat, as I shall explain, it is possible to have prepared bulbs in flower at Christmas The showy trumpet flowers, which appear before the leaves, are available in such colours as red, pink, orange and white.

Start the bulbs into growth in February using the John lnnes No. 2 Potting Compost and leaving the upper part of the bulbs uncovered. The drainage provided must be good, for these plants should not be repotted more than once every three or four years as they do not take kindly to root disturbance. Provide a temperature of 16° C. (60° F.) and start watering when growth begins, increasing the amounts as the plants develop. Remove some of the compost from the top of the pots in spring and topdress with new compost. This must be done very carefully.’

After flowering and when the leaves have developed, feed the plants with liquid manure to build up the bulbs for the following year. Also, place the pots in a sunny position to ripen off the bulbs.

With the summer drawing to a close the foliage will start to turn yellow and this is the time to reduce the amount of water given, until eventually the compost is quite dry. When this stage is reached lay the pots on their side under the greenhouse staging. This is my method, but some gardeners prefer, I know, to keep the compost just slightly moist so that the bulbs are not completely rested. Increase from seeds or offsets.

The prepared hippeastrums for Christmas and winter flowering which I mentioned earlier, are a good proposition. A bright red variety offered in this way is called Winter Joy. The bulbs are started into growth in early November and are potted as described for other hippeastrums. These need, though, a temperature of 21° C. (70° F.) to flower for Christmas. Given lower temperatures they will flower from mid-January onwards.

Hyacinths Hyacinths. The much-loved, fragrant hyacinths need no introduction. pot the bulbs in early September or as soon thereafter as possible in John limes No. 1 Potting Compost. Place one bulb in a 4 in. pot or three in a 6 in. pot partly exposing the bulbs and place out of doors under ashes. After about 10 weeks move the pots into a cold frame and a week or so later bring them into the greenhouse. Start watering when growth begins and increase the quantities progressively. Plant the bulbs in the garden after flowering.

Especially prepared hyacinth bulbs for Christmas flowering are available in red, pink, blue, yellow and white. My favourite named varieties for forcing are the soft pink Princess Margaret, Pink Pearl, the blue Myosotis, the splendid red Jan Bos and the salmon-pink Lady Derby. For an early display, too, there are the Roman hyacinths with their loose spikes of fragrant white and pink flowers.

Iris Iris. The dwarf bulbous iris like I. reticulata and I. histrioides may be grown in pans in a cold greenhouse. A 3 in. pot will accommodate several plants and they like a mixture of equal parts loam, leaf-mould and sand. They should be potted 1 in. deep in September. Keep them in a cold frame until growth begins and then move them to the greenhouse. Start watering at the same time and increase the quantities later. Cease watering when the leaves wither after flowering. Dutch and English iris can be grown in this same way except that these need 5 in. pots instead of 3 in. The Dutch iris Wedgwood, pale blue with a yellow blotch, is one I find very good for growing in pots.

Ixia (African Corn Lily) Ixia (African Corn Lily). I find these quite attractive as pot plants, when grown five or six to a 5 in. pot. They do not, however, like to be forced too much and should be kept. In cool conditions although they like plenty of sunshine. The flowers are of many colours and are borne in spring.

Pot the corms 1 in. deep in September, October or November in a mixture of equal parts loam, peat and sand. Plunge in a cold frame until growth begins and then bring them into the greenhouse. Always water with care, but especially so in the winter months.

Lachenalia (Cape Cowslip) Lachenalia (Cape Cowslip). The lachenalias are splendid cool greenhouse plants and their pretty name is descriptive, for these South African plants have bell-shaped, cowslip-like flowers. There are many named hybrids in a lovely range of colours, and two others which have been grown for many years are the golden-yellow L. abides nelsonii and L. bulbifera (or L. pendula as it is often listed in catalogues) which includes coral-red, yellow, purple and green in its floral colours. The ‘pendula’ comes from the flower spikes which are rather pendulous. The leaves are also an attractive feature of the plant, often being handsomely mottled.

Pot the bulbs in August using the John Innes No. 1 Potting Compost and just covering their tips. A good show will be provided by potting six bulbs in a 5 in. pot. Place the pots in a cold frame until growth is made and then transfer the plants to a shelf in the greenhouse and provide them with a temperature of 7° to 10° C. (45° to 50° F.). Water with particular care in the early stages and give increasing amounts as the plants develop. Dry the plants off slowly after flowering and ripen the bulbs in full sun.

Muscari (Grape Hyacinth) Muscari (Grape Hyacinth). The muscari make pleasing pot plants and Muscari armeniacum Heavenly Blue in particular is often grown in this way. Pot the bulbs in September or October and plunge in a cold frame until growth starts, then bring them into a cool greenhouse. Use a compost consisting of 2 parts loam, 1 part peat and 1 part sand, and plant about 15 bulbs in a 5 in. pot, setting them 1 in. below the surface of the compost.

Nerine (Guernsey Lily) Nerine (Guernsey Lily). The colourful nerine hybrids are excellent for autumn colour in the cool greenhouse. pot the bulbs half exposed into a 4 ½ in. pot, in August or September and use a compost consisting of 2 parts loam, 1 part leaf-mould and 1 part sand. Place the pots in a cold frame and water very little until growth appears, when they should be moved to the greenhouse. The amount of water given should now be progressively increased and continued until the leaves die down, when the plants should be rested in cool conditions.

Scarborough Lily, see Vallota

Scilla (Squill) Scilla (Squill). The scillas, and especially Scilla sibirica, are popular for greenhouse cultivation. Pot between August and November 1 in. deep in a mixture of 2 parts loam, 1 part peat and 1 part sand. Plunge them out of doors until growth starts and then bring them into the greenhouse.

Snowdrop, see Galanthus

Sparaxis Sparaxis. The 1 to 2 ft. long spikes of violet-purple flowers of Sparaxis grandiflora are a welcome addition to the greenhouse in spring. Pot the corms in November and plunge in a cold frame until growth begins. Then move to a greenhouse with a temperature of 4° to 10° C. (40° to 50° F.) increasing to 16° C. (60° F.) in spring. Water the plants carefully at all times.

Tigridia (Tiger Flower) Tigridia. The colourful Tigridia pavonia is a fine plant for an unheated greenhouse with its showy and distinctive orange-red, spotted flowers. pot the corms in March or April in John Innes No. 1 Potting Compost and plunge in a cold frame until growth begins. Then move to the greenhouse. Water carefully when growth begins and more liberally later. After flowering give decreasing amounts of water and when the foliage has withered stop watering altogether until it is time to start the growth cycle again in the spring.

Tritonia Tritonia. The tritonia usually offered is T. crocata, a pretty plant of about 1 ft. in height with reddish-orange cup-shaped flowers which are borne in April and May. This is a plant for the cool greenhouse needing a minimum temperature of 4° C. (40°F.) during the winter months and 10° C. (50° F.) from March to September. I use the John Innes No. 1 Potting Compost for this plant and place eight corms 3 in. deep in a 5 in. pot in September or early October. These are kept in a cold frame until growth begins and they are then placed on a shelf near the glass in the greenhouse. Water with discretion when growth starts and increase the supplies later but always exercise care when carrying out this task. Partially dry off the corms after flowering. Increase by seed or by dividing the mature plants.

Tulips see Tips for Planting Tulip Bulbs

Vallota (Scarborough Lily)

Vallota (Scarborough Lily). Vallota speciosa, known to so many gardeners under its common name, is a very easy bulbous plant to grow well, either in the greenhouse or the home. It is a showy plant, too, with its handsome red trumpet flowers. These appear in late summer.

Pot in March in John Innes No. 1 Potting Compost, one bulb to a 5 in. pot, and allow the plants to become root-bound, for in that condition they seem to flower better. Repot old plants in June or July, when this becomes necessary, say once every three or four years. They need plentiful supplies of water from spring to early summer but less from then to September. Only moderate amounts of water should be given from autumn to spring. Increase from offsets.

Zantedeschia (Arum Lily) Zantedeschia (Arum Lily). This genus has been known in the past as Arum, Calla and Richardia, which is all a bit confusing, but this plant with its prominent spathes is well worth growing for spring display. The species usually grown is the white Zantedeschia aethiopica but there are also two yellow-flowered species, Z. elliottiana and. Z. angustiloba (Z. pentlandiz), which are rather more difficult to grow and need more heat.

Pot the fleshy roots of Z. aethiopica in August or September using the John Innes No. 1 Potting Compost and pots of 5, 7 or 8 in. size depending on the size of the roots. Stand the pots outdoors or in a cold frame for about four weeks and then bring them into a cool greenhouse. They need plenty of water.

After flowering has finished decrease the supplies of water, increase the ventilation, and early in June, after danger of frost has passed, stand them in the open until it is time to start them into growth again. Increase is from suckers.

Zephyranthes (Zephyr Flower, Flower of the West Wind) Zephyranthes (Flower of the West Wind). These dainty flowers, 6 to 8 in. high, are attractive for the cool greenhouse. The most frequently grown is the white Z. candida; others are Z. rosea, pink, and Z. ajax, pale yellow. They like a compost of 2 parts loam, 1 part peat and 1 part sand and can be potted between August and November. Water very little until growth starts and then increase supplies considerably. Dry off the bulbs after flowering.

06. October 2010 by Dave Pinkney
Categories: Bulbous Plants, Greenhouse Gardening, Plants & Trees | Tags: , , | Comments Off on Planting Flower Bulbs for the Greenhouse


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