Fobroary 15, 1877. ) 



JOUKNAIi OF HORTICULTURE AND COTTAGE GARDENER. 



Ill 



WEEKLY CALENDAR. 



WHEN TO GIVE AIE, AND WHY. 



ff . ^ HO dares say anytliing against the tinie- 

 lionoui'ed " chiak of air " insisted on by 

 so many first-iate gardeners? It would 

 seem at first sight to be ahnost madness 

 to do so, and at the same time to own 

 th.at probably the greatest number of 

 successes are to be found at present where 

 the said chink is held in great veneration. 

 Nevertheless I say unhesitatingly that the 

 necessity for the chink of air on forcing 

 houses night and day in winter is only an imaginary one, 

 and to keep it on regularly is extravagance. 



As a general rule, houses which have their roofs con- 

 structed principally of glass do not require opening at all 

 so long as the atmospheric temperature has to be assisted 

 by fire heat. Those who recommend a constant chink of 

 air imagine it is necessary for the sake of supplying the 

 plants with fresh air, and this idea when looked at in the 

 right light is altogether an absurdity, and will only be- 

 come reasonable when our glass fittings are made air- 

 proof. Imagine a forcing house at 70' while the outside 

 temperature is 30" ! A good arithmetician could tell you 

 how long it would take, if shut as closely as possible, 

 to change its air entirely. I have not the least idea of 

 the length of time it would take, but certainly net many 

 hours, and of course with a gre'ater difference between 

 the two temperatures the more rapid would be the change ; 

 consequently the less need would there be to open the 

 ■ventilators. Anyone who will look at the matter for a 

 moment will see that it takes at least four times the 

 amount of hot-water pipes to heat a forcing house that it 

 would to heat a dwelling house to the same temperature ; 

 and again, a forcing house well covered or double-glazed 

 will take a third less fuel than it otherwise would to keep 

 it up to the required temperature. All this goes to prove 

 that in an ordinary forcing house when the outside tem- 

 perature is low the change of air is sufficiently rapid for 

 the good of the plants. 



Not only is fuel wasted by giving air when the plants 

 have already a sufficiency of it, but the tissues of the 

 plants are dried up, and they become an easier prey to 

 insects. I know there are people, and good gardeners 

 amongst them, who will scarcely credit that it is possible 

 to force Kidney Beans, Strawberries, &c., in winter with- 

 out red spider. Let all such banish their old notions about 

 giving the constant chink of air and high artificial tempe- 

 ratures, and they will find that it is easier to go on with- 

 out this and other pests than it was with them. By-the- 

 by, I find high night temperatures, the venerable chink 

 of au% and a plague of insects keep company very con- 

 stantly. I have often been at a loss to understand how 

 so many of our good gardeners wUl insist on a high night 

 temperature and declare that thiir plants will not exist 

 under the conditions, and often name, say, for instance, 

 55° for Cucumbers and Vines in full growtli. Now I think 

 the chink of air must have something to do with it. We 

 know that we may feel quite comfortable as to warmth 



No. 829.-VOL. XXXU., New Series. 



at one time with the thermometer at 40°, but an east or 

 north-east wind will speedily deprive us of that comfort, 

 though the thermometer may declare the temperature to 

 be 55°. 



When and why is it necessary to open the ventilators ? 



Istly, When there is not sufficient difference between 

 internal and external temperatures to cause circalation 

 and consequent renewal of air. 



2ndly, When blossoms are expanded which require 

 fertilisation, a more rapid circulation than usual is neces- 

 sary to dry and distribute the pollen. 



3rdly, Wlien there is a likelihood of the temperature 

 rising too high or too rapidly from natural causes (not 

 after it has risen, mind ; the rising must be anticipated). 



A rapid rise of temperature does not harm many hot- 

 house plants, escepting they are bearing fruit or flowers, 

 when, owing to the fruit and tJowers not being wai-med 

 so quickly as the surrounding air, moisture immediately 

 condenses on them, and is very injurious. The same 

 cause produces damping or fogging-off with small or 

 tender plants. If the temperature rises rapidly while the 

 soil is comparatively cold condensation takes place on 

 the surface and speedily affects the stem where it touches. 

 A low temperature, even when approaching a frosty one, 

 is not injurious of itself to ripe Grapes ; but when the 

 natural temperature rises suddenly while the Grapes are 

 still cold and condensation takes place on them, as was 

 so well explained by " A Nokthekn Gardener "recently, 

 injury very soon follows. The only safe plan is to just 

 keep the pipes from becoming entirely cold and to run as 

 if for your life to open the ventilators when the sun is 

 likely to show itself. 



Keeping a regular temperature of 40°, 50°, or any other 

 fancied height is all nonsense. You cannot do it. If the 

 outside air is 55°, your vinery with ripe Grapes must be 

 00°, or the fruit will soon rot from damp. Heating and 

 ventilation attended to, the amount of moisture in the 

 house is of little consequence. We are still (February 5) 

 using Hamburgh Grapes which have been kept ia a house 

 with thousands of bedding plants which received an 

 abundance of water two or three times a-week all through 

 the worst winter months perhaps ever experienced. I 

 must not, however, take too much credit upon myself 

 for this, tor a great deal belongs to the house, which is 

 probably one of the best in the country. — Wm. Taylor. 



THE WHITE LILAC, 



AS PREPARED ANDiFORCED IN FRANCE. 



The white LDac, which is extensively used in the forma- 

 tion of bouquets in Paris from the month of October, has 

 been an object of much interest. The cultivation of this 

 shrub, the colour of which is lilac when grown naturally 

 in the open air, appears a mystery to many who are not 

 initiated into the secrets of horticulture. It is, however, 

 quite simple and practicable even for modest amateurs. 



The Lilac Charles X. is preferable to aU others for this 

 mode of culture ; it alone is employed for this special 

 culture. Take up in autumn a clump, or only a part, 



No. 1481.— Vol. LVIL, Old Series. 



