Feeling the heat: Temperature and fertilizer's role in cooking up a high yielding raspberry crop ( Rubus idaeus ) grown in a controlled, indoor, hydroponic environment.

Abstract

Background: Temperature and fertilizer crucially influence fruit quality. While well-studied for outdoor-grown red raspberries, optimal conditions for controlled indoor agriculture are less understood.

Objectives: This study aimed to identify the best temperature and fertilizer regimen to maximize fruit production, sweetness, and harvest index in an indoor, hydroponic vertical farm.

Methods: We tested three temperatures (21, 23, 25°C) and three fertilizer mixes (A: weak fertilizer applied at a constant rate, B: developmentally adjusted fertilizer (DAF) and C: DAF plus commercial endomycorrhizal fungi) on 'Joan J' raspberries in a controlled indoor hydroponic vertical farm in Toronto, Canada. We measured fruit number, weight, and sugar content.

Results: Raspberries grown at 23°C produced significantly more (∼30%) total fruit biomass than those at 21 and 25°C (F = 17.19, P<0.001). Fruit weight was higher earlier in the season, decreasing by 29% in the following three months. Temperature and time interacted such that the largest fruit was produced at 21°C in the first month (F = 3.70, P < 0.001). Fertilizer B yielded significantly greater (26-35%) more fruit and harvest index than Fertilizers A or C (F=5.16, P<0.001), though no significant differences were found in the interaction between fertilizer and time. Additionally, raspberries grown at 23°C had significantly higher sugar content (9.89°Bx, P < 0.05) compared to other temperatures, but fertilizer did not influence sweetness.

Conclusions: While 21°C yielded the most fruit early in the season, 23°C produced the highest overall yield and sweetest fruit, lower than typical outdoor conditions for temperate climate raspberries. Developmentally adjusted fertilizers increase raspberry yield.