Our goal to overwinter plants indoors is to achieve slow growth with superior health. These plants will give our butterfly garden a huge head start when they are replanted next spring. You can do this too!
The following tips are all the things I wish someone would have told me before I made my first attempt to overwinter butterfly plants:
1. Cut back foliage before bringing pots inside
The only reason to leave lots of foliage on overwintering plants is if you want to give unwelcome garden pests a good place to hide. I cut back most plants, including tropical milkweed, to about a foot.
2. Hose down your pots/plant before bringing them in
It’s a lot easier (and less messy)to clean the grime off pots before you take them inside. After spraying down with water, you can also spray the cut back plant with isopropyl alcohol to eliminate any trespassing pests…don’t forget to spray under the leaves!
3. Spray and water plants with a mix of water and hydrogen peroxide
I was a fool who believed that after our plants were cut back (with no bugs in sight) they would remain pest-free for the winter. Little did I know that fungus gnat eggs, hiding under the soil, were about to hatch an alternative plan. By the time I realized these gnarly gnats had invaded our basement, they were already a major problem, killing two of our smaller tropical plants.
The next season, I treated all our plants with hydrogen peroxide (H2O2) to prevent this issue. H2O2 kills gnat larvae on contact. Hydrogen peroxide also helps your plants grow by putting more oxygen into the soil. Many plant diseases and fungus are the result of low oxygen levels in the roots. The extra oxygen molecule (O2) in the soil will help prevent root rot.
I apply hydrogen peroxide according to this helpful chart:
Hydrogen peroxide chart for plant use (I treat our plants according to the sick/fungusy chart and all plants have exhibited healthy growth with no fungus gnat issues…)
Spraying also raises the humidity level for optimal plant growth.
tip: Water the container plants with hydrogen peroxide just before you bring them in and throughout the winter.
tip 2: For adult fungus gnats, see #9
4. Put a plant saucer under each pot
This keeps dirty water from potentially soiling your floors or creating slip hazards.
5. Have adequate lighting available
In past seasons I have only used natural window lighting on plants. This has worked well for tropical milkweed and most plants.
Now I use additional light sources in the form of CFL (compact fluorescent) light bulbs. I’m using two 40 watt bulbs (each equivalent to a 200 watt regular bulb) and a 25 watt bulb (equivalent to a 100 watt bulb). I am using full spectrum bulbs that simulate natural daylight. The plants get approximately 10 hours of light each day.
You should be able to find these bulbs at big box stores like Lowe’s or Home Depot. The 3 bulbs I purchased were less than 30 dollars total, and you might not need that many.
You can also find them online if that’s more convenient:
LED Full Spectrum Grow Lights for Indoor Seedlings and Plants (we’ve been using these lights with adjustable arms to overwinter butterfly plants indoors since 2019)
I put the 40 watt bulbs into a standard ceiling outlet and the 25 watt bulb is in a portable goose neck lamp.
6. Keep your thermostat around 65° F (18.3° C) give or take a few degrees. Warmer temps help create the breeding ground for plant diseases and pests.
7. Don’t overwater
Moisture is the accomplice of both plant disease and fungus gnats. It’s OK if your plants dry out a little…especially since fungus gnat larvae can’t survive in dry soil. All containers should also have adequate drainage.
8. Make sure there is good air circulation
I use a clip-on oscillating fan when I first bring in tropical plants. Why? To prevent overly humid conditions where pests can potentially thrive. Some might say this is counterintuitive to plant health, but I’d rather deal with dryer conditions than bug infestations. Once the threat-level is safely at green, the fan is removed.
Last winter we didn’t use a fan and had no issues with fungus gnats. I believe the key to success is treating butterfly plants with the h202 mix (tip number 4) early to stop the infestation before it begins.
9. Pest Control
If you see aphids on milkweed or other plants, stop them before they become an issue by trying idea #1, #3, #8 or #9 from this aphid-control post.
10. Water When?
I used to water once a week, but discovered this was too much water for some plants. Water a plant when the top couple inches of soil start to look and feel noticeably dry.
11. Going Away on a Long Trip?
Discover how you can leave your butterfly plants for up to two weeks without hiring a plant sitter:
12. Moving Plants Back Outside in Spring
Plants go through an adjustment period when being moved outdoors and should not be placed in full sun to avoid scorching the leaves. Expose overwintered plants to sun gradually over a few weeks.
If overwintering Asclepias curassavica, take stem cuttings in early spring to start new tropical milkweed plants.
If your intention is to use tropical milkweed for spring monarchs, take stem cuttings earlier in fall or winter.
Regardless of your set up, some plants will do better than others and there will be trial and error involved. Be prepared to lose a few plants along the way, but hopefully you will learn what works through this experience.
I have no doubt there are other potential issues I have yet to encounter. However, I continue to improve on my success each winter, and my happy spring plants are living proof…