How to warm up a greenhouse with citrus trees?

Maja B
November 28, 2019

Hello guys, sorry in advance for a long post, but I need your help with some questions about citrus trees in the winter and warming up a greenhouse in the winter. Main problems and questions are in bold.

So, a month ago I transferred all my plants (citrus trees, raspberry and lemon seedlings, fig and peach tree) indoors in a greenhouse which has a big LED light above it so it can give light to plants, since we do not have a lot or any sunlight during winter in the room where the plastic greenhouse is set. Also, nowadays the temperatures are around 0-9 Celsius, and in next few days the temp is gonna drop around -3 Celsius (cca 20-40 Fahrenheit) during the night and day.

Last winter, the leaves of a citrus trees have fallen down, leaving a bare branch tree. Also, one citrus tree in the summer has new buds of leaves, but then all of a sudden those tiny leaves fall during the night and next morning (they cant sustain on a tree to give 3rd and 4th branches so that tree has not bloomed yet although it is 5 years old). Why? All trees above mentioned are in fresh and nutritious soil, and not root-bound. I fertilized them every 2 weeks (in the summer and spring), according to labels on liquid fertilizer, and every 3 weeks they receive a spray of sea algae for micronutrients. As for the winter period, they are given 3-month-fertilizer which has NPK and all macro and micronutrients. I do not use mulch (should I?).

So, I have them in a plastic greenhouse in a room which temperature is almost like the outside temperature (maybe few degrees more). Leaves of trees and seedling have fallen down because there was a big shock in temperatures outside (we had cca 25 Celsius, and then immediately 5-10 Celsius) and because there was not enough light (I have secured a big LED light for that last part). I am warming the soil twice or thrice a day with bottles with warm water and with winter covering + I have put sawdust in plastic bags and put the bags on top of the soil, but that is not still enough during the night and partly during the day. All Christmas light I have at home are LED which do not provide much heat, and I do not want to use the electricity heaters because I cannot watch out for them all the time + I dont want a bigger electricity bill at the end of the month. Is there any other way to warm up plants to dry the soil from watering and to warm up the whole greenhouse? The temperature should be around 10 Celsius, and the lemon and raspberry seedling are not holding very well (they dont grow anymore + the raspberry seedling leaves are turning brownish because the soil cannot dry completely).

Thanks in advance :)

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