Lemon Culture in New Zealand

New Zealand Journal of Agriculture, Volume 68, Issue 5, 15 May 1944, Page 341

Lemon Culture in New Zealand

By

W. K. DALLAS

(N.D.H.N.Z.),

Director, Horticulture Division, Wellington.

(Continued.) Planting For heavy or moderately heavy soils that are liable to remain cold and sodden during the winter months spring planting is preferable to autumn planting, since the soil is in better condition after lying fallow during the winter. Further, as the trees are set out in soil which is becoming warmer, the roots soon establish themselves. Autumn planting is suited to most welldrained soils provided the land is well worked prior to planting. The trees should be planted on the square system, ’ as. this facilitates cultivation. Trees, to be set out on betterclass land should be planted from 22 ft. to 25 ft. apart. The former requires 90 trees per acre and the latter 69 trees per acre. It is not advisable, however, to plant trees closer than 25 ft., as a less distance does not allow for the land between the trees to be effec-

tively worked or cover-crops grown when the trees reach full stature. On less fertile soils they may be planted 20. ft. apart. At this distance 108 trees per acre are required. For the purposes of economical working, as well as general appearance, it is important'that the trees be planted in lines, so that from whatever point, they are viewed the rows look perfectly straight. Full details in connection with the laying-out of an orchard may be obtained from the Horticulture Division, Department of Agriculture, Wellington. ■ The sites for the trees having been marked with pegs, the holes should be dug and the soil removed and scattered broadcast. Before planting it is advisable to mix lime, superphosphate, and bone-dust together of lime, two of superphosphate, and one of bone—and to place six handfuls of the mixture into each hole and work it

well into the soil. If not attended to when heeled-in the roots of the youhg trees should be examined and damaged parts cut off. In the process of transplanting there is always some loss of roots. The tops should be lightened to balance this loss/ as it is difficult to re-establish a free with a head heavy in proportion to the roots. This may be effected by removing superfluous branchesthree to four main branches being sufficient to make the foundation of a tree —or by shortening growths as the case may require, or by both removing and shortening shoots. When a young tree is furnished with spreading roots it is well to make a mound in the centre of the hole, on which to place the tree with the roots pointing down the sides of the mound. The soil for filling in is obtained by digging the surrounding soil forward. The advantage of this method is threefold: it breaks down the walls of the hole, does away with a possible pot-hole for water, and ensures that nothing but top soil will come in contact with the roots. If the soil is of a heavy nature the filling-in should be done with a digging-fork. It is advisable to tread the soil firmly over the roots but to leave the surface soil loose. During the planting operations the roots should not be left exposed to wind or allowed to become dry. To neglect this precaution may cause a loss of trees. Pruning / In the study of the methods adopted for the pruning of lemon-trees it is found that a great many trees are not pruned sufficiently. While over-prun-ing is not recommended, the pruning should be sufficient to maintain a fairly open-headed tree furnished with a good supply of thrifty fruiting laterals. Except for the winter and early spring months, pruning may be carried out at any season of the year. The most suitable period, particularly

if heavy cutting has to be resorted to, is in the spring at the commencement of tree-growth, when the wound-gum is present in sufficient quantity to protect the tissues against the entrance of disease through the wounds. Pruning in the Nursery The pruning of the tree should begin with the one-year rod from the bud. The height at which the one-year tree should be cut will depend upon the height that it is desired to make the head. For convenience in working the orchard the tendency now is to prune the rod back to a height of about 3 ft. from the ground. It is, however, advisable to cut a little higher for the following reasons: Firstly, it is impossible to be sure of keeping the top shoot. Top shoots are frequently strong in growth, and until well on in the season

their hold on the main stem is not too secure. In windy places they are liable to be blown off, which may be disastrous to the development of a wellbalanced tree if other suitable branches are not available. Secondly, some trees send up the first shoots too near to the perpendicular. If the young tree is headed a little higher than the top branch is required the upper shoots tend to spread, and so the desired angle to form a broad base to the trees is obtained. Further, there are other branches to select from in case any are blown off. During the first year after the head-ing-back of the rod, the shoots which develop should not be touched as the tree needs as much foliage as possible with which to develop a good rootsystem, strong branches, and to protect the trunk from the sun.

In the second year the branches to form the framework should ,be selected. Each tree should have from three to four main branches, the distance between the lowest and highest being from 10 in. to 12-in. The lowest branch should be at least 2 ft. from the ground. The branches should be arranged spirally on the trunk and not opposite each other, because when leaders are in whorls they are liable under stress to break away from the trunk. Those branches which are not required should be removed carefully. Pruning at Time of Planting Young trees received from the nursery in most instances are branched trees two years from the bud with the head already formed. When the young trees are planted shoots not required should be removed in order to restore

the balance between the top and the root. Normally the selected branches do not need shortening, but where they have made very strong growth it may be desirable to head them back'. The trunks should be protected from sun-scald either by white-washing or by wrapping newspaper or other suitable material around them. Pruning of Non-Bearing Trees During the first three years after planting very little pruning is necessary—merely sufficient to keep the trees upright, to develop a shapely open, balanced head, and to remove superfluous shoots. Branches which are growing strongly to the detriment of others may require heading-in to increase the strength of weaker branches and to induce lateral growth. The trees should have as many leaders as will fully furnish the tree without crowding. 4 •' . . There are a number of methods adopted by' growers to develop the framework of the trees. One method which gives a tree of the desired symmetrical form and openness of head is to select three or four leaders, which should be inclined at about a 45 deg. angle. This should be done at the end of the second or the third year after planting, when the trees are well established and strong growth has been made. Of the vertical growths which arise from the leaders two strong wellspaced vertical shoots should be selected. Other, vertical shoots should be either kept in subjection or removed, and the leader shortened back to the outside selected vertical growth. Two years later, when the selected shoots have made strong growth, each should be cut back to two suitably placed strong lateral shoots, thus doubling the number of leaders. From the vertical shoots which arise from these laterals one shoot on each should be chosen, and two years later, when these selected shoots have made strong growth, each should be shortened back to a strong lateral growth. The . treatment of the past two years should be repeated until the trees reach a height of 10 ft. In most situations the . trees should not be allowed to exceed 10 ft. to 12 ft. in height, as such a height allows of much of the fruit being gathered from the ground and of pruning and spraying being more readily carried out. This system of training provides shapely trees, each having from 12 to 16 leaders which should carry heavy crops without undue bending. The centre of the trees should not be allowed to become filled with vigorous shoots. ? > Young lemon trees should receive attention two or three times a year for the purpose of cutting back branches that are outgrowing the remainder of the tree and to remove suckers, especially should they arise from the trunks of the young trees.

Pruning of Bearing Trees To maintain a maximum supply of fruiting wood the stronger subsidiary lateral growths should be pinched back to cause them to send out fruiting wood nearer to their base and close to the main branches. Trees with an open centre carry fruit both. on the inside as well as on the outside of the trees. The lower growth should be kept well above the ground-level and all straggling shoots and branches,cut back to preserve as nearly as possible an even contour in the whole, tree. All brush (unthrifty lateral . growth), ■ watershoots, and • dead and dying wood appearing in the tree should be pruned out entirely. If the wood is young and vigorous the fruit will develop better, and much of it will mature in the summer. Growth that has been injured by frost should be cut back to sound

tissue. A fairly open head in the tree fosters fruiting laterals and facilitates effective spraying. When a tree is allowed to grow with little or no attention it may produce a fair crop for a time, but much of the fruit will be on the ends of branches where it is liable to sway with the wind and become rubbed and bruised. Branches may be also broken by the weight of fruit, thus reducing the productiveness of the tree. To keep the mature tree shapely and fruitful it is desir able, that it should receive attention at least once a year. Neglected trees are difficult to spray and often become infected with fungous diseases and infested with insect pests to an otherwise avoidable degree. The Lisbon, being an extremely thorny variety, requires more thorough and regular pruning than the other

varieties, if fruit is to be obtained free from thorn injury The inside of the tree must also be made accessible to the picker so that without undue difficulty he may avoid thorn scratches. Thorns on the main limbs

should be reduced by pruning at the time of picking. The Eureka lemon requires more shortening back of the laterals and reduction in tree heights, as its habit of growth is that of a tip-bearer. The

lemons set at the end of long lateral growth are blown by every wind thus resulting m rind abrasions and injury. The Genoa, Villa Franca and eyer develop more symmetrical - shaped

trees. The Meyer is somewhat similar to the sweet orange in its habit of growth—closer headed. In the main the trees require only a thinning out of the shoots, which tend to become dense where annual pruning is neglected. . Tools and Wound-Covering. Sharp secateurs to enable smooth cuts to be made are essential as are also a sharp saw, and a knife to smooth off the tissues ruptured by the use of the saw. A protective wound-covering should be applied to all wounds over half an inch in diameter. Gather and Destroy Prunings. should be gathered and burnt without undue delay, to get rid of prunings that are diseased, to maintain the general tidiness, and to improve the hygienic conditions pertaining to the orchard. Cultivation The depth to which the soil may be cultivated is governed by type of soil and depth of rooting of the trees. As there is a tendency for young lemontrees to develop roots near the surface the ploughing during the first few years should be relatively deep near the trees. The space around the trees not reached by the plough should be hand-dug, and any roots met with near the surface severed close to the trunk by a clean cut. As the trees increase in size the ploughing; . should be restricted to the area outside the spread of the trees, and the ground beneath the trees can then only be surfacecultivated. When this stage of the tree development is reached the trees will have a well-established root system in the middle and lower strata of soil. The importance of a good depth of well-cultivated soil cannot be too strongly emphasised, because unless this is provided the roots cannot long remain sufficiently active to maintain growth and produce continuously heavy crops of fruit suitable for commercial purposes. The amount and character of cultivation, however, given to an orchard must be governed to a large extent by the nature of the soil and the climate. Usually it is best to plough to' a depth of from 6 in. to 8 in. in the autumn and cross-plough in the spring. During the summer months the surface should be kept loose with a cultivator, ploughing at that time being inadvisable, as it tends to dry out the soil. In the autumn the first furrows may be turned up against or towards the trees and an open furrow left in the middle 1 of each “land” between the trees. In the spring the order is reversed, and thus the soil is brought back to its original position. The spring ploughing should be done as early as practicable, either in August or early September, and should cover all weeds and trash lying on the

ground. The soil .should then be worked down to a fine tilth, which should be maintained throughout the summer. The ground under the trees should be dug over to a depth of from 5 in. to 6 in. at least three times a year. In working soil where the main mass of feeding roots have been allowed to become established close to the surface the depth of cultivation should not be so deep as to cause a serious loss of roots. The effect of cultivation upon the soil organisms (bacteria, fungi, and protozoa) is often overlooked. It is to these countless silent workers that a rich soil mainly owes its fertility. Thorough aeration, obtained only by cultivation and good drainage, is necessary for the micro-organisms to thrive and carry on their important work of soil improvement.

Cover Crops For the successful growing of lemons it is essential to have a soil with a high humus-content. Besides assisting with the elaboration of plant-foods, especially nitrogen, organic matter increases the capacity of the soil to retain moisture and improves the aeration of the soil. The humus-content should be built up by green manuring before planting the orchard, and while the trees are young and deep ploughing is possible. To maintain the trees in thrifty condition after they have come into bearing cover-cropping should be continued. Legumes are most suitable for cover crops, since they grow rapidly and are rich in nitrogenous matter. Those recommended are horse-beans, lupins, vetches, and field peas used either

alone or in combination with oats, barley, etc. A mixture of equal quantities of superphosphate and carbonate of lime often may be broadcasted profitably with cover crops at the rate of 6 cwt. per acre. In some districts weed-growth may be sufficient to maintain an adequate humus-content of the soil. During the early summer weeds, on account of their demand upon soil-moisture, should be suppressed, but when early autumn rains are experienced they may be allowed to grow. When the herbage of weeds is allowed to grow it would be good practice to augment it with a legume broadcast early in February to come - up in advance of the weeds. Before ploughing a green crop under it is good practice to cut it into pieces with the discs, as this ensures a more even distribution of the organic matter. A green crop should not be

ploughed in while the soil is in a dry state, unless it be in the late autumn with winter rains soon to follow. A fair amount of soil-moisture is- necessary to ensure the. decay, as when moisture is in scant supply the crop decays very slowly. Green manuring should not be carried out during the later part of. the spring or .summer, since the bulk of the material may remain undecomposed thus keeping the soil open with a consequent loss of valuable moisture. It is recognised that a green crop ploughed into the soil may have at first a temporary impoverishing effect, reducing for a time the available nitrogen. It is therefore necessary that green crops should be turned in at a time when the trees are requiring a minimum amount of nitrogen, this being about midwinter. Soil-moisture is usually abundant at this time, and decomposition should be well advanced before the trees reach full activity.

For the first four or five years vegetable crops may be grown between the rows of trees. It usually is advisable to manure for these crops, and they should not be planted so close to the trees as to interfere with the young roots. If these matters are attended to intercropping is beneficial, as the cultivation necessary for the crops improves the condition of the soil. Potatoes, kumaras, tomatoes, peas, beans, and other leguminous crops are. suitable. (To be Continued).