In the late fall we received a question from a Chicago Botanic Garden patron who was planning-ahead to taking care of their first bonsai, a Juniper tree, in the winter. After researching online, they asked questions about watering, fertilizing the tree, and where to keep the tree over the winter.

Answer:

Welcome to the Bonsai community.

It sounds like you've gotten some good advice so far. You are correct to water whenever the soil feels dry right up until temperatures stay below freezing, at that point the plant will dramatically slow down its water intake. Watch the temperatures outside for long periods above freezing where the plant may begin taking up water again and could need a watering.

Outside in a cooler as you described is a fine way to keep your tree over winter. The only things I would add are to bury the pot fully in the straw, up to the lowest branch of the tree to reduce possible evaporation from the soil, and to ensure the cooler has an open drain so it will not fill with water and potentially drown the tree. Junipers will actually benefit from receiving some light over the cold months, so a spot with some sun would be best, and by all means, let the rain and snow fall naturally on it.

As for fertilization, once a month with miracle grow mixed for houseplants will do fine. There's no need to fertilize over the winter, however, as the plant will not take up any nutrients during dormancy. April is probably the best time to start feeding again.

This past fall we received a question about over-wintering a Satsuki Azalea. Writing in about a tree they received in the spring, after keeping the tree outside all summer, the writer noticed that the tree was starting to have yellowing leaves, and some were becoming dry. They weren’t sure how to take care of the tree over the winter in Chicagoland.

Answer:

Azaleas require a wintering period, but are not as cold hardy as we would like around here. It is important to try not to let the root ball freeze, while still giving the plant the cooler temps it needs to lignify and set buds. Azaleas like winter temps between 33 and 40 degrees. The best solution I have been given would be an attached, but unheated garage with a small grow light for the plant. (Apparently they will weaken if kept in full darkness) I would put the pot in a box and surround it with styrofoam peanuts or something else to buffer any sudden temperature swings and check it occasionally to see that the soil stays moist.