Overwintering Cool and Dark

Deciduous plants drop their foliage at the end of the growing season as the days get shorter and the temperatures 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.

Most plants that lose their leaves, or wilt its above-ground parts, like deciduous trees, shrubs and perennials, including many tuberous plants need cool, dark overwintering conditions.

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.

What to do now

1. 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.

2. 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 immediately.

3. 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.

   Recommended temperature for this plant:

4. 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 or stop completely.

5. Stop fertilizing
   During the time your plant is resting, it won't need any fertilizing. Planta automatically adjusts for this.

Tubers, bulbs, rhizomes

Plants that overwinter as bulbs, corms, rhizomes, tubers or other underground parts of the plant don’t need any light either.

• Reduce the watering or place the pot somewhere sheltered from rain late in the season when the night time temperatures drop close to the lower limit of the plant (if outside). Keeping the plant and the bulbs on the dry side reduces 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. It can be a good idea to leave the bag partially open the first couple of weeks, or make small holes for ventilation.

Winter watering tubers

You might see watering tasks scheduled in the app for your tuberous plants during their dormant period. Disregard the standard instructions and instead use these reminders as a chance to check on the tuber or bulb. If the soil is bone dry and you notice the bulb itself is starting to shrivel or look a bit dehydrated you can lightly mist the soil or the tuber rather than giving it a full watering. This will prevent it from drying out completely before it is time to wake it up for spring again, and also avoid overwatering and rot.
If the tuber still feels firm and plump you can simply skip that task instead.

If a tuber starts growing early

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 lower temperature (within the acceptable range). Many bulbs tolerate being planted deeper or having their shoots trimmed before planting in spring, with no noticeable difference in growth the following season.

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, greenhouse or other sheltered room outdoors for the winter. It doesn't matter if it's a bright or dark location.

• 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. In that case, skip the "Prepare for winter" task scheduled for the plant, and Planta will automatically adjust the watering interval to be more frequent and adapted for a skipped dormancy.

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 can make them weak in the long run, or sometimes result in a lack of blooms the following year.