Overwintering Cool and Dark
Deciduous plants drop their foliage at the end of the growing season as the days get shorter and the temperature drop. This means they don’t need much light throughout the winter months as long as they’re placed in cooler temperatures during their winter dormancy. This preferred growing space is often a little easier to find compared to plants that need both a bright and cool winter.
Most deciduous trees, shrubs and perennials, including many tuberous plants cool, dark overwintering conditions.
You can find information in Planta about what type of overwintering your plant will need - whether that's somewhere bright or dark. This will be in your plant's Plant info tab.
For plants that aren't winter hardy
This includes all your plants that don’t tolerate the temperature outdoors during the winter months, but still need it cooler than regular indoor temperatures. Finding a cooler room that is kept frost free works best for most species but you can double check this under the tab Plant info in Planta.
What to do now
Prepare the plant - When the night time temperatures start to drop to the lower limit your plant tolerates, you can start moving it to the spot you’re going to winterize it in. Planta helps you water the plant less frequently, but we still recommend being observant so that it doesn’t stand in wet soil. Snooze the watering task if the soil is still wet.
Let the plant go dormant - Your plant might have lost most of its foliage by now, or at least started to. If it hasn’t, temporarily keeping it cool and bright until they drop by themselves is preferred. This enables the plant to winterize and enter its dormancy better, with lower risk of it trying to grow in the darkness later on.
Move the plant - Place your plant in a cool room. For example a garage, shed, basement, attic, summerhouse or a cool stairway if you are living in an apartment. Some plants can also be placed on a sheltered or enclosed balcony, if you keep control of the temperature (so it doesn't get too cold). Recommended temperature for this plant:
Check your plant for any potential pests - They are much easier to fight when the plant has lost its foliage and the temperature is lower. They also will reproduce at a much lower rate.
Stop fertilizing - During the time your plant is resting, it won't need any fertilizing.
Tubers, bulbs, rhizomes
Plants that overwinter as bulbs, corms, rhizomes, tubers or other underground parts of the plant don’t need any light either.
Lower the watering or place the pot somewhere sheltered from rain later in the season when the night time temperatures drop close to the lower limit of the plant - keeping the plant and the bulbs drier decreases the risk of rot.
Either move the whole pot to the overwintering spot as it is, or harvest the bulbs or tubers when the foliage has wilted. Most big tubers are best kept dug down in a pot or box with sand or other porous material to prevent rot. This includes Dahlia, Begonia, Canna, Gladiolus and others.
Smaller rhizomes and bulbs can be harvested and kept in zip lock bags in pure vermiculite to help regulate an even humidity. Note that it’s very important to check them regularly and let the bag air out a little if condensation starts to build up.
Some plants might start to emerge with weak, pale shoots in the later part of the winter or early spring. This can to some extent be prevented with a low temperature. Many plants tolerate being planted deeper or having the shoots trimmed off before spring.
Winter hardy plants
When it comes to plants that are cold hardy in your area, it’s good to know that these too need some winter protection if grown in a pot. The hardiness for a plant is based on it being grown and established in the ground. Grown in a pot, it’s much more exposed to sudden changes in temperatures as the roots are not as insulated. When the temperatures drop in fall, prepare your plant in any of the following ways:
Place it in a shed or other sheltered room outdoors for the winter
If you can't move it, wrap the pot in some burlap or similar insulating material, add mulch or leaves on top of the soil and place the pot against the house wall. If possible, shelter your plants from strong winds.
Another option that is very effective is to dig the whole pot down into a flower bed, the ground or a compost. Rake some leaves up against the base of the plant to insulate extra. This will prevent both severe freezing of the roots, but also keep them from warming up too fast in spring.
What happens if I skip an overwintering?
Sometimes you don’t have a choice and can’t overwinter your plants in a cool, frost free environment. If the outdoor climate most likely will kill them, you don’t have any other option than to keep on growing them in a bright spot indoors. Since the schedule in Planta is set for overwintering your plant somewhere cool and dark, we recommend you to set a custom schedule for watering and fertilizing during the winter months.
Go to the plant > Settings > Set Custom Care Schedule
Plants that have evolved to go dormant during the colder/darker season of the year can become stressed if not allowed to go dormant. This might make them weaker in the long run.