Asparagus ferns are beautiful ornamentals that are considered to be low-maintenance. However, they don’t tolerate the cold very well, so you’ll need to help yours get through the freezing winters by overwintering them. With proper care, your asparagus fern will thrive for years to come.
To overwinter an asparagus fern:
- Move your asparagus fern indoors.
- Prune dead or spindly leaves and stems.
- Protect your plant from the cold.
- Give your fern sufficient sunlight.
- Increase the humidity.
- Be wary of stagnant water.
In this article, I’ll walk you through the overwintering process step by step. Let’s get started!
1. Move Your Asparagus Fern Indoors
Asparagus ferns are native to hotter climates, which is why they don’t have built-in protection from the cold. You should bring your asparagus ferns indoors before nighttime temperatures fall below 55 °F (13 °C).
Even in the absence of temperature control, your plant will feel much warmer indoors than it will outdoors. This is especially true at night, as temperatures outside can easily drop below freezing.
Sub-zero temperatures are particularly dangerous because they cause the water within plant cells to freeze up. The frozen water forms sharp crystals and expands (water is one of the few elements that expand when they freeze).
As a result, cell walls are torn open, and the plant dies from within. Damage done by frost is irreversible, so it’s best to avoid it in the first place.
Important note: Asparagus ferns are mildly toxic to humans and common pets, such as cats and dogs. Don’t allow your pets to nibble on the plant, and keep it out of their reach.
Transplanting Your Plant to a Pot
If your asparagus fern is planted in an outdoor garden, you’ll have to transplant it into a pot. You can use a standard ceramic pot or any appropriately sized container of your choosing.
However, your container of choice should have a drainage hole to prevent overwatering. Overwatering is a great risk to plants.
Additionally, you should use some high-quality potting mix to host your asparagus fern. It has extra nutrients, which will help your fern stay healthy during the winter.
I don’t recommend using regular soil from your garden, especially if you’re still a beginner. Garden soil can be contaminated with fungi, pests, and pathogens, which you risk bringing indoors.
As for the transplantation itself, it’s best done sooner rather than later. Your asparagus fern will need some time to acclimate to its new environment, and you don’t want it to be fighting off the cold at the same time.
Leaving Your Fern in the Outdoor Garden
I recommend bringing your asparagus fern indoors to ensure its survival, but if you live in US hardiness zones 11 or higher, you can safely leave the plant outdoors.
It won’t fare well and will probably lose most of its foliage during the winter, but it will live to regrow beautifully next year.
However, in lower hardiness zones, you should bring the fern indoors. Frost damage due to sub-zero temperatures is irreversible, and your fern won’t regrow.
2. Prune Dead or Spindly Leaves and Stems
It’s time to give your asparagus fern a haircut.
If you’ve brought your asparagus fern indoors, go ahead and prune off any dead, weak, or spindly leaves. Remove any undesirable matter from the plant. You can even cut off wasteful stems.
It’s important to wear gloves while pruning and use a sanitary cutting tool.
Your asparagus fern will fare better through winter if it has less plant body to feed. Nutrient reserves will be utilized more efficiently and last longer.
Severely damaged plant matter takes time and energy to heal. It’s always better to prune it off because the plant can then redirect the same energy toward new growth or life-sustaining functions.
Now, I don’t recommend cutting down your asparagus fern if you’ve chosen to leave it outside. Some gardeners cut it down at this time to prepare for new growth after the winter and because the foliage will die during the winter anyway, but there’s a little-known benefit to leaving the plant foliage as it is.
When this foliage dies on its own during the winter, it will form a cover on top of the plant’s base. This natural layer of dead foliage will act as a blanket against snow and provide insulation to keep your asparagus fern’s vital parts warmer.
You can always cut off or remove the foliage after the worst of winter has passed. Your asparagus fern will grow all the same when temperatures return to normal.
3. Protect Your Plant From the Cold
It’s as simple as it sounds. Do what you can to increase the relative temperature your asparagus fern experiences.
You can do this in a few ways:
Keep It in a Heated Room
Keep the fern in a heated room with a temperature of above 70 °F (21 °C). If that’s not possible, opt for a room that’s naturally warmer. Smaller rooms, rooms with many electronic appliances, and rooms with lots of sunlight tend to be warmer. South-facing windows and garages are excellent.
Spread a Layer of Mulch on the Soil
You can spread mulch for both potted and soil-based plants. Mulch not only helps regulate temperature by providing insulation but also slowly releases nutrients into the soil. It’s made up of organic matter, which has a host of other benefits.
Cover the Fern at Night
Cover your asparagus fern with a sheet during nighttime. This is ideal when temperatures fall to their lowest. Remove the sheet when the sun comes back up to let the plant get its fair share of sunlight.
Using these simple methods, you can increase the local temperature your asparagus fern is exposed to, even when overall temperatures are far lower.
4. Give Your Fern Sufficient Sunlight
You should place your asparagus fern near unobstructed south-facing windows. This location receives the most amount of sunlight throughout the day, which is essential during winter.
Locking your asparagus fern in a dark and empty basement for an entire season is a sure way to kill it. You’ll need to use an LED grow light to compensate for the lack of sunlight.
These lights are must-haves if you’re looking to place plants in dark rooms, whether it be for decorative or storage purposes.
5. Increase the Humidity
Asparagus ferns love high-humidity environments, much more so than the average plant. In fact, low humidity conditions (which are typical in heated rooms during the winter) can cause their health to deteriorate visibly.
Now, there are a couple of ways you can increase humidity and keep your plant from drying out.
You can always use a humidifier to maintain the humidity levels around 60%. These appliances are convenient, precise, and work automatically. However, there are alternatives if you don’t have one.
Or, you can use a pebble tray. This is one of my favorite ways to increase the local humidity around a plant. It’s a tray lined with sizable rocks and pebbles.
Water is added to the tray until it sits just below the peak height of the pebbles. You then place your pot/container on the pebble tray. As water evaporates from the tray, it moisturizes and hydrates your fern.
The best part about using a pebble tray is that you increase only local humidity. The change in the overall humidity of the room is negligible.
Important note: You should always keep your asparagus ferns away from vents and radiators, especially when you’re trying to increase the humidity. Heated air drafts will suck the moisture out of your asparagus fern quickly, and it will suffer from dehydration as a result.
6. Be Wary of Stagnant Water
Stagnant water is something you never want to leave unaddressed, but it becomes even more of a threat during winters because evaporation slows down.
The dangers of overwatering are not to be underestimated. Too much water in the soil cuts off the oxygen supply to the roots of your fern. The oxygen-deprived roots will die, and the plant will follow.
Plants need less water during winter, to begin with, so you should be more conservative with your watering schedule.
The best way to manage your asparagus fern’s moisture needs during winter is to keep watering to a minimum while maintaining a higher humidity around your plant. That said, you must wait until the top 2 inches (5 cm) of the soil is dry before adding more water.
Asparagus ferns are tender but low-maintenance plants that are more than capable of looking after themselves. However, they are vulnerable to the winter cold, as they don’t have any natural protection against it.
Before winter hits, you should:
- Bring your asparagus fern indoors.
- Prune off the damaged or wilted leaves and stems.
- Provide it with heat and insulation.
- Place it near sunlight or use LED grow lights.
- Take steps to increase humidity.
- Adjust your watering routine to account for the slower rate of evaporation.
With a little bit of care, asparagus ferns will easily make it to spring.