This is the practice of encouraging plants to flower or fruit too soon . The simple form of forcing is done by inverting a tub over rhubarb crowns to encourage blanched increment . likewise rhubarb , sea - kale , dandelion and chicory can be forced under the greenhouse staging in mild heating system and darkness , which also blanches these crop , rendering them more palatable .
Another very simple method of forcing is to turn off sprays of winter or spring‑flowering shrubs such asJasminum nudiflorumand forsythia in bud and place them in a warm way to bestow out the flowers before those out of doors blush . The sudden change from very cold to warm encourages quick growing and is employed in the forcing of flower bulbs . It has been found that some bulbs make good and speedier increment under precondition of forcing if they are pretreated by cold storage .
daffodil , in picky , respond to this treatment , and are put in cold computer memory for several weeks during August and September before being force . Pre - care for medulla such as ‘ gilded Harvest ’ and ‘ Carlton ’ are usable to amateurs . hyacinth , too , are offer as pre - handle bulbs , such varieties as ` Ostra ’ , ‘ Pink Pearl ’ and ‘ Jan Bos ’ responding well . They should be institute as soon as they are received , otherwise normal temperature will nullify the cool off intervention .
The grandness of keep newlyplanted bulbsfor force in really cool weather ab initio , can not be overemphasize . A good root system has to be modernise before quick growth can be expect , and it is in very coolheaded conditions that settle formation takes topographic point . Whether pre - cooled or not , bulbs can be forced byartificial Light Within , where natural light can be excluded completely and the common temperatures for electric-light bulb forcing be maintained 65 - 75 ° F ( 18 - 24 ° C ) .
Light is presenter , for any back-to-back twelve hours of the twenty - four and one 100 - W lamp is sufficient for 1 satisfying meter ( yard ) of bulb when put on 90 cm ( 3 foot ) above the bowls or box . Commercially the use of such uprise rooms is increasing , and artificial light is used in the polish of chrysanthemum to provide flower all the year round , by a system of forcing and delaying . Considerable progress is also being made in the use of goods and services of carbon dioxide to enrich the atmosphere of both growing rooms and glasshouse , to advance quick growth , once leave-taking are form , of such crop as lettuce , cucumber , tomato and chrysanthemum .
Many shrubs can be brought into flower early for nursery show ( or once they are bloom they can be change to the house for way decoration ) in late winter or early spring . Young plant can be lifted from the terra firma or , bought especially , pot up and brought into the greenhouse about New Year . Keep a buoyant atmospheric state and coolheaded conditions for two or three hebdomad then increase the temperature step by step , watering and feed as required . Such plant asDeutziagracilis , Prunus triloba , Native American azalea , forsythia , philadelphus , syringa , hydrangea and spiraea , answer well to this case of cultivation but it is overbold not to hale the same plants year after twelvemonth .
