Container grown hebes: A study of their responses to different nutrient levels : A dissertation submitted in partial fulfilment of the requirements for the post graduate Diploma in Horticultural Science at Lincoln University

Abstract

Five pot experiments using composted bark medium were conducted to study the influence of nutrition on container grown hebes. These experiments were conducted in a heated glasshouse equipped with automatic fan ventilation where temperatures ranged from 13.5⁰c to 22.5⁰c, shading of 15% and with supplementary lighting, giving extended daylengths of up to sixteen hours. The plants were hand-watered when required. Plants were sprayed regularly with a general purpose insecticide-fungicide mixture and in addition were sprayed for white fly when necessary.

Two different Hebes, diosmifolia and 'Eveline', were grown to see if species differences occurred.

Experiment 1 - Nutrition: Hebe diosmifolia was fertilized with combinations of 5 levels each of N, P and lime: 0-160gm N/m³ /month, 0-80gm P/m³ /month and 0 -16kg Lime/m³ . All plants were also given a set amount of magnesium, potassium and micronutrients. The experiment was a three factor central composite 2nd order rotatable complete block design.

Experiment 2 - Nutrition: Hebe 'Eveline' - A repeat of experiment 1 but with a different species. Experiment 3 - pH: A) H.diosmifolia B) H. 'Eveline'

Plants were fertilized with 5 levels of lime and the medium levels of N and P of experiments 1 & 2: 80gm N/m³ /month, 40gm P/m3 /month and 0-16kg Lime/m³ . All plants were also given a set amount of magnesium, potassium and micronutrients. Each experiment ( 3A & 3B) was a simple non-factorial randomised block design.

Experiment 4 - Nutrition: H.diosmifolia only. This experiment was set up to see if in fact there was a potassium response. Plants were fertilized with combinations of 5 levels each of N, P, K and lime: 0-160gm N/m³ /month, 0-80gm P/m³ /month, 0-120gm K/m³ /month and 0-16kg Lime/m³ . All plants were also given a set amount of Mg and micronutrients. The experiment was a four factor central composite 2nd order rotatable complete block design.

Both hebes responded strongly to N, with optimums being in the range: 80- 128gm/m³ /month for H.diosmifolia and 128-160gm/m³ /month for H. 'Eveline', depending on the response measured. Little response to P was found, with the .larger number of responses for 'Eveline'. Optimum growth for both hebes at · 40gm P/m³ /month. No significant response to K by H.diosmifolia was found. H.diosmifolia showed a strong negative response to lime, and H. 'Eveline' showed it to a lesser extent. Optimum growth was produced for both hebes at Okg/m³ Lime, a pH of 5.08 in this medium. No significant nutrient interactions were obtained.