My Tropical Wintering System

by Ken Goebel

Winters in Minnesota can be chilling, with average high’s in the 20’s and lows in the 0’s deg. F.  In the summer months I grow my tropical trees outdoors in a small 8 x 8 x 8 ft. greenhouse constructed of reinforced polycarbonate.  Plenty of sunlight permeates the greenhouse and the tropicals can be kept in there all summer, but I put them outside during the hottest months of July and August for fresh air.  There are thermostated heater fans inside to keep the temperature higher than 60 deg. F.  With this setup the greenhouse extends my outside tropical season from April until November, but the trees still need to be kept indoors during the winter months.
In the winter I keep these trees indoors inside a framed shelter that I built with full spectrum fluorescent lights overhead.  The lights are supported by a metal frame, and can be adjusted up or down.  This metal support for indoor plants can be obtained at various nurseries.  A wood framed shelter was built around the fluorescent lights and metal frame using cedar strips permanently fastened to a cedar base.

Winter enclosure with fluorescent lights and plastic tent rolled up above

 Indoor Setup

There is clear plastic sheet on the top and all the sides to maintain humidity at about 65 %, and temperature about 70 deg. F through the winter months. The unit is facing south and west windows to gather natural window light as well as the fluorescents.  The lights are on a timer for 12-16 hours daily.  Each tree has a humidity tray with aquarium gravel underneath.  The plastic sheet is loose along the frame edges for easy access to the trees.


Various accessories can be placed inside the indoor enclosure to make the environment as pleasant as possible for the trees. 

Accessories including fly paper, humidity/temperature monitor, crane, and scholars accents, and small DC fans


The fly paper can be hung on a cedar strip, and along with the fan circulating the air, discourages flies and fungal infestation.  The fan runs on two D cell batteries which need to be replaced every 1-2 months.  Otherwise the fan can be wired and connected to an adapter that converts ac to 3 volts dc.  The monitor indicates if the humidity or temperature is too low.  And the accents add ‘atmosphere’ and make the plants feel right at home.

My bonsai collection consists of about 30 outdoor trees, and saikei and penjing landscapes.  As I am growing older, I am slowly reducing the number of my outdoor trees, and acquiring more indoor trees.  My collection of indoor trees presently is five tropicals.


Ficus burtt-davyi with heavy trunk


This is a ficus I acquired from Jim Smith’s personal collection, a shohin burtt-davyi.  It has a" pig style" trunk and my wife says it has warts on the branches, so I have named it the “warthog”.
Texas ebony

 Texas Ebony

I got this a year ago as Texas Ebony stock from a Florida nursery.  I have styled this myself from scratch.  It was a bush when I received it.  Now about 21 inches tall.


 Fukien TeanFukien tea

I was the winning bid on this tree at this month’s October Minnesota. Bonsai Society auction.  About 14 inches tall.


Green Island fig, Ficus microcarpa

 Green island Fig

You might recognize this one.  Last spring I was lucky enough to acquire this Green Island ficus in ‘epiphytic’ style from Jim Smith’s personal collection.  And Jim informed me that he also made the pot!  You have a picture of this identical tree and pot in your “Ficus The Exotic Bonsai” book on page 74, picture 28. 
Willow Leaf fig group planting

 Willow Leaf Group

Last spring I acquired a 12 inch tall willow leaf ficus as FL nursery stock.  I exfoliated and styled it and potted in a nice Chinese zisha pot.  It looks like a triple trunk, but the two smaller trunks were given to me from a bonsai friend who specializes in indoor bonsai.  He gave them to me as trunk stub cuttings, no roots, no branches, no leaves, a couple of years ago.  So I rooted them in acidic rooting soil and potted them along with the tall stock to make it appear as a triple trunk bonsai.
These tropicals are being kept in the indoor enclosure over the winter.  During the winter my tropicals are fertilized about once a month, with low nitrogen, liquid fertilizer, such as N-P-K of 2-7-7 or 0-10-10.  The trees will still experience some dormancy due to less winter sunshine, and low N fertilizer allows them to rest before next growing season.  And winter watering is reduced as well, 1-2 times weekly, allowing the soil to go bone dry before top watering and light foliage misting.

You can see more of my work and writing at my website at http://mypenjing.kdgwild.com



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