With their exuberant flowering and the Mediterranean or tropical ‘look’, tub plants are real atmosphere creators. Most are not hardy and must hibernate in a frost-free area. Because there is a chance of night frost after October 15, they should be indoors before that time. Or not? Groei & Bloei asked two experts for wintering tips.
Roel Vonk is head of the greenhouse complex in the Botanical Gardens of Utrecht. Bert Rijken is secretary of the Southwest region of the Nederland Tublantenvereniging, a national club with about six hundred enthusiastic members who want to promote the use of container plants. They have the following tips for you …
10 wintering tips
1. Stop fertilizing on time
It is important to only give the plants fertilizer with a low nitrogen content (N) and a relatively high amount of phosphorus (P) and potash (K) from August. Do not give fertilizer at all from September.
2. Make sure that the root ball does not get too wet
If the plants enter with a wet root ball, there is a risk that the roots will rot. Therefore, place them under a roof or under the garden table for a while before taking them in, so that the rain cannot reach them.
3. Bring the plants inside as late as possible
Plants that stay outside for a long time are more resilient. So bring them inside as late as possible, but in the meantime pay attention to the weather forecast and take the origin of your plants into account. Pay extra attention to young plants, which are more sensitive to frost than older ones.
4. Pack it
The roots of plants are always less resistant to frost than the above-ground parts, and this applies even more to plants in pots. Good to know: special sleeves are available for (temporary) ‘packing’ plants in pots.
Almost all container plants are evergreen, which makes them susceptible to drying out. There is a chance of this, especially with a poor, easterly wind. Provide a sheltered spot as long as they remain outside and water occasionally during drought.
6. Deciduous or evergreen?
Suitable wintering places for evergreen container plants (e.g. oleander and Callistemon) are a greenhouse or a cool room. Deciduous species (e.g. tubers) can also hibernate in the dark (garage, crawl space).
7. Correct temperature, light, and water
Most container plants require a temperature between 5 and 12 °C, but some want it colder or warmer. The site of the kuipplanten Vereniging contains a list of the wintering requirements per species in terms of temperature, light, and water requirements.
8. Fleece against the cold
In general, a room that is slightly too warm is less harmful than when it is (long) too cold. If the latter is the case, wrap the plants (lightly) with a non-woven cloth.
9. Don’t let it dry up
Water very moderately during the winter, but make sure that the plants do not dry out. Problems often arise due to wetness rather than drought
10. Wintering addresses
Do you not have suitable accommodation for your container plant (s)? There are also wintering addresses at growers and garden centers. There you can overwinter container plants for a fee.
Tub plant association
When it comes to wintering, members of the Tub Plant Association have it easy. The association rents an old greenhouse in Elshout, where they can bring their plants. The 3000 square meter greenhouse was completely full last winter. The plants can be brought from the first to the last week of October. Most are pruned before moving in.
Less chance of night frost?
It is said that non-hardy plants are increasingly surviving winters. However, that does not mean that the risk of early night frost has decreased. Could the temperatures have been less extreme in recent years? According to Jordi Bloem of Meteo Consult, this is not the case. “With little wind, a snow cover, and a supply of cold air, it can still freeze locally by twenty degrees.