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ISHS Acta Horticulturae 31: Symposium on Potplants


Author:   O. Voigt Christensen
DOI:   10.17660/ActaHortic.1973.31.19
When growing pot plants, the heterogeneous growth and development of the plants can be seen at the time of sale. In this connection deformed and other unusual plants are not counted. Heterogeneous plants have to be sorted out, if the grower wants to sell homogeneous plants. Next the plants are replaced, to wait for the next batch of salable plants, which are then removed for sale, the plants replaced again and so on. If the grower has to sell the whole quantity at one time, he has to sort out the plants in different salable sizes and perhaps disregard some of the small plants which are not salable. In both cases it can be seen that it is expensive to produce heterogeneous plants. Production planning is very difficult with non-uniform plants, and production planning is becoming more and more important. In other words, if the plants are made homogeneous, it will decrease production costs and make production planning possible.

It is also possible to reduce the cost of production by growing the plants at optimum growing-conditions. In this way the production time will be shortened.

The results of these two different efforts, homogeneous growth and optimum growing-conditions are illustrated in fig. 1. It is assumed that the optimum growing-conditions do not decrease the plant heterogeneity (however, see later). Curve 1 represents the sale of a quantity of plants over a certain time, under current growing. Curve 2 shows the quantity of plants after growing with optimum conditions and curve 3 after reduction of the heterogeneity.

When the effort is put forward to make a homogeneous plant, it should be used in making the new quantity as good as the best plant in the previous quantity.

The standard deviation in a quantity of plants is usually symmetrical around the mean, and the aim is to decrease the standard deviation. The effort therefore is to make a quantity of plants which have a small standard deviation and utilize the best quality in the quantity of plants. In fig. 2 is shown the spread for 2 curves with the same mean (1 and 2), but with different standard deviations. Curve 3 has the same standard deviation as curve 2 but a different mean. The aim is to make a quantity of plants which have a mean and standard deviation as shown by curve 3, because the effort is the same when making a quantity of plants which represent curve 3, as when making a quantity of plants which represent curve 2.

It is necessary to know the reason for the heterogeneity of a quantity of plants. The reasons can be classified as follows:

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