Matt Fleming, Smithsonian Garden Tropical Plant Specialist has just a few things to reiterate or further explain about wintering over tropical plants:
I know I said this 100 times during the presentation and it’s not what many of you want to hear but… there are SOOO many factors that go into determining the best overwintering conditions for tropicals  (plant hardiness/needs, light levels of where plants are being overwintered, what Plant Hardiness Zone you live in, etc.), but it is best to learn about each plant you want to overwinter and its individual needs and act accordingly”.   

I didn’t go into much detail about actively growing plants and where they should be kept over the winter, but again it is going to depend on the situation.  How many plants are you keeping?  How much light do you have to offer?  You will have to make decisions about which plants get the best light levels or move them every few weeks to help.   

Lastly, have fun with overwintering.  You will make mistakes and kill things but that’s ok.  Live and learn.  Your local extension agency is a great resource for questions and concerns.   

Resources 

Specific information on plants visit the Missouri Botanical Garden Plant Finder.  

Q & A from the webinar 

Q–My banana tree stays in the ground and I put bags of mulch over it.  Do you have any better suggestions? 

A–There are so many banana varieties that it’s hard to give a specific answer here, but I’d say if it’s working for you keep doing it.  I will say I’d rather have you spread the mulch 4-6” thick over the plant instead of piling on actual bags of mulch; you can use leaves or straw as well.  Make sure it’s in well–drained soil to avoid having ‘wet feet’ over the winter. 

Q–Tips for bringing in herbs from the garden? 

A–Depending on your situation, I would pot them if needed and put them somewhere with a lot of light.  You can put them in a slightly shady location before bringing them in to help with adjusting to the change in light levels.  They will probably drop some leaves at first but will flush again.  Misting them will often help as well. 

Q–Where and how do you store bulbs/rhizomes once you dig them up? 

A–As a general rule, let a light frost hit them or when they start to die back on their own you can dig them up.  Lay them somewhere to dry out and brush off as much soil as possible.  You can store them in a box with dry peat moss, vermiculite, sawdust, or even shredded newspaper.  Do not store them in plastic bags.  I would keep them in a cool, dark place if possible (cool being plant–specific but 50˚F is a good rule of thumb).  Just as an example, many caladiums prefer being stored at 60˚F, so it’s best to learn about each plant’s individual needs.   

Q–What should you do if you want to cultivate a plant from an area that’s not native like a tropical plant in a cold environment? 

A–This is done all over the world in cooler climates.  Whatever plant you want to grow just be sure to learn about its needs, specifically its cold hardiness.  Bring it inside as needed and enjoy. 

Q–I have a hedicium (ginger) in the ground that’s about to flower. What’s the lowest temperature it can stand? How should I overwinter it? 

A–There are about 75 Hedychium species so it is hard to give an exact answer.  I would research your specific species and see what its hardiness is.  All Hedychium I have cared for go dormant so I would suggest making it easy on yourself and let it go dormant as well. 

Q– I have a small anthurium that I’ve sort of kept alive. It’s in bloom right now. Should I bring it in soon? 

A–Most anthuriums are pretty sensitive to cold.  Without knowing where you live, I’d say keep an eye on night temperatures and bring it in when they start to hit the low 60’s.   

Q–Please address saving Zingiber that is planted outside and will be stored in a greenhouse. 

A–If it’s in a container let it start to yellow outside then cut back the stems to a few inches.  You can pretty much stop watering over the winter and come late February start to bring it out of dormancy.   

Q– What are you looking for when you lift up a pot to check for water? 

A–I’m actually not looking for anything, but I am feeling the weight of the plant/pot to tell how dry or wet the entire root ball is, not just the top 1” of the soil.  Dry soil is MUCH lighter than wet soil.  You can get a feel for the weight by testing it: let the plant dry out (not totally), lift it a few times, then water it and lift it again.  After a while you will learn to tell how dry your plant is by testing the weight of the pot. 

Q–Is there a way to figure out the right watering routine? 

A–This is probably the most asked question and is nearly impossible to answer.  There are so many factors: plant vs. pot size, light levels (in the house and even is it a sunny week or a cloudy week), obviously different plants like various levels of water.  My suggestions are to do the lifting technique described above or stick your finger in the top 2” of soil and see if it is dry or wet.  As you water and get more familiar with each plant you will learn its needs.   

Q–How often should one spray plants for scale or spider mites before bringing them inside? 

A–I wouldn’t necessarily spray just to spray, but if you see an issue each pest is slightly different.  With most insects (aside from scale), if you spray two times 7-10 days apart that should take care of the problem.  Scale on the other hand is difficult to control as many are only vulnerable to sprays in the crawler stage.  If it’s a small infestation I’d either squish them by hand or cut off affected parts.  If it’s a major issue and you really want to save the plant you might have to drench it with a systemic insecticide.    

Q–After getting rid of all mealy bugs before bringing a plant in, they always reappear in February. Any ideas? 

A–Unfortunately, pests are a part of growing plants; trust me, I deal with this on a daily basis.  Just try to keep a healthy plant by watering it correctly.  The earlier you catch any issues, the easier they are to control, so every time you water give your plants a good once over to scout for any issues.   

Q–You advise that plants should go in cool, dark place inside. If there is a little light, such as on a windowsill or in front of a patio door, should the plants go there? 

A–When I referred to a cool, dark place, that was for plants that go dormant or semi-dormant.  Any actively growing plants should be put near the sunniest locations available including windows, sliding doors, or whatever you have available.   

Q–How do you get caladium bulbs through the winter to regrow again next year? Mine always dry out! 

A–Try to dig them up about as late as possible, then the foliage will have time to send any nutrients to the bulbs.  Caladiums are a little more cold–sensitive than many other bulbs and appreciate temperatures closer to 60˚F for winter storage.  Like any living thing, bulbs have a life span and will decline from year to year.  

Q–What about putting bulbs in a refrigerator as long as there is no moisture buildup?  

A–After some quick research I found that most residential refrigerators are kept between 37-42˚F.  For nearly all tropical bulbs, tubers, etc. that temperature range is too cold.  As a result, I advise against this.   

 Q—What did you mean when you talked about ‘healing over’? 

A—I mentioned healing over when I touched on divided plants.  What I mean by that is when you dig up or divide plant bulbs, rhizomes, etc., they can get sliced or broken.  These wounds need time to ‘callus’ over in order not to rot.  That’s one reason why after digging up bulbs and similar plant forms it is important to let them dry out somewhere before packing them up for the winter.