- Examples of palm species
- Basic measures for winter protection
- Methods for overwintering outplanted palm trees
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Palm trees in free range are mainly known from the tropics and subtropics, rather less from Germany. Nevertheless, empirical values from the last ten to twenty years show that a year-round outdoor cultivation of palm trees is no longer a rarity in this country either. But not every species is suitable for planting and especially for wintering outdoors. Whether and how a palm species can overwinter in the garden depends on various factors.
Examples of palm species
- Mazari palm 'Nannorrhops ritchiana' to - 26 °C
- Needle palm 'Rhapidophyllum hystix' down to - 25 °C
- Dwarf palmetto palm 'Sabal minor' down to - 24 °C
- Chinese hemp palm 'Trachycarpus fortunei' to - 17 °C
- Dwarf palm 'Chamaerops humilis' down to -14 °C
- Blue hesperid palm 'Brahea Armata' to - 10 °C
- Rock palm 'Brahea dulcis' down to - 8 °C
Not hardy species
- Bamboo palm 'Chamaedorea seifrizii'
- Mountain Palm 'Chamaedorea'
- Triangular palm 'Dypsis decaryi'
- Kentia Palm 'Howea'
- Date Palm 'Phoenix'
Basic measures for winter protection
Protect root area
The rougher the situation, the more complex the protective measures for the root area. You can prepare it for the winter when you plant it, for example by laying a suitable heating cable in the root area.
- Among other things, heating cables for water pipes or gutters are suitable
- These usually have a control unit with a temperature sensor
- Control unit starts up as soon as temperatures fall below 5 °C
- There should be no risk of overheating
- To install the cable, prepare the planting hole accordingly
- Line the vertical walls of the planting pit with polystyrene sheets that are at least 5 cm thick
- Floor remains completely free
- Fasten the heating cable to the styrofoam plates
- Then fill with well-drained soil
- Cover the root area additionally with bark mulch, leaves, straw or pine twigs
Tip: Everyone has to decide for themselves whether they want to take on all the effort to spend the winter. Not every climate lends itself to growing palms outdoors all year round, and even more winter protection would be tantamount to a heated greenhouse.
Frost sensitivity of outplanted palm trees
Even if year-round outdoor cultivation is not common practice in this country, it can certainly be successful under certain conditions. Of course, this assumes that you choose sufficiently hardy species. Basically, the frost hardiness is genetically determined and can vary slightly from specimen to specimen within the same species.
The root area and immature plant tissue that is still growing are most sensitive to frost. Consequently, the winter protection must be adapted to the prevailing climatic conditions in order to bring these attractive plants safely through the cold season. In addition to the species, the site conditions, the age of the palm and the duration and intensity of a frost period play an important role in frost hardness or overwintering.
Pay attention to optimal site conditions
Each palm species has its own individual requirements for an outdoor location, i.e. in terms of temperature, light conditions, water and nutrient supply. Light and temperature cannot be separated from each other, because the temperature level also rises with increasing solar radiation. Optimum winter protection begins with planting. Both summer and winter conditions must be taken into account here, because in every garden there are colder and warmer areas.
- Warmer areas in the garden, left to the most sensitive palm species
- Strong wind, heavy rain and snowfall, often the cause of leaf damage
- Palm trees naturally need a lot of warmth
- Prefers a sunny spot outdoors all year round
- During growth, temperatures of at least 10-18 °C and a maximum of 20-30 °C
- This facilitates regeneration after frost damage
- Other important factors are soil and air moisture
- Humid air leaves ice crystals on the leaves
- These ice crystals reduce frost tolerance
- Soil that is too moist can cause lasting damage to palm trees
- Year-round protected locations with permeable soil ideal for overwintering
Consider the age of the palm
Young and freshly planted palm trees are much more sensitive to frost than older ones, especially during prolonged, severe frosts. Therefore, they need a little more protection for wintering. The roots are particularly sensitive. In young palm trees, they don't go that deep into the ground and, in the worst case, could freeze to death completely. As a result, they can neither absorb nor transport water, and the palm dries up. Due to their large leaf surface, palm trees also evaporate water in winter and are therefore dependent on a functioning water supply even in the cold season. Older specimens are much less sensitive.
Duration and intensity of the frost period
Most palm trees planted outdoors survive short periods of frost relatively easily. However, not every species of palm reacts the same way to frost and every species has its own frost limit. While some need strong winter protection, others cope very well with cold and sub-zero temperatures. In the case of planted palm trees, in most cases appropriate protection for overwintering is only recommended during longer periods of frost.
Do not apply winter protection too early
Immature plant tissue is particularly sensitive to frost. For this reason, it is important to stop fertilizing from August so that the tissue is mature and therefore more resistant before the first frosts. When it comes to winter protection, less is often more. In order to prepare the plants for the winter, they should be slowly acclimated to colder temperatures.
You can do this by being careful not to pack them too early or when there is a slight night frost. Covering too early would result in the plant having poor frost tolerance, which in turn significantly increases its susceptibility to frost. Every winter protection measure means an impairment that, in the worst case, can do more harm than good to the plant. Nevertheless, one should not exhaust the frost hardiness of a palm tree, as this could result in massive frost damage in spring.
It is all the more important to choose the right time to attach the winter protection. As soon as the outside temperatures approach the respective tolerance limit of the palm to + 5 °C, it is time to attach the winter protection. So if a palm species can tolerate temperatures between minus 12 °C and minus 17 °C, it should be protected from a temperature of minus 7 °C. Depending on the frost hardiness of the individual palm species, more or less protection may be required.
Methods for overwintering outplanted palm trees
In mild locations
- In areas with mild winters, light antifreeze is usually sufficient
- If frost is announced, loosely tie the leaves together in different places
- Preferably use coconut or sisal cord for tying
- Tying together protects the heart of the plant in particular
- Unsuitable wire for binding, it could cut into the leaves
- Do not bind leaves too tightly
- There must be ventilation between the fronds
- This prevents rot and mold growth
- Additionally protect young plants with fleece
- Wrap fleece around leaves and stem (if present).
This additional protection can be dispensed with for older specimens in regions with mild winters. On warmer, frost-free days it is advisable to unwrap the wrap to allow light to penetrate and any condensation to evaporate. In order to protect the root area sufficiently, cover it extensively with a thick layer of mulch, dry leaves or straw.Washingtonia robusta
Tip: Snow on the fronds generally has an insulating effect. However, its weight can cause the fronds to snap, so be sure to shake it off the plant to be on the safe side.
In locations with moderately severe frosts
In order to hibernate in cooler regions, the fronds are loosely tied together again with appropriate cords. The space between the fronds can be filled with dry leaves or straw to protect the heart even better. Merely tying them together is not enough, the leaves must also be wrapped with an air-permeable frost protection fleece, reed or bamboo mats. The whole thing is loosely fixed again. Depending on the type of palm, this wrapping should also cover the upper end of the trunk. On several consecutive days without frost, the covering should be opened or removed and the plant ventilated.
In regions with severe frost
In areas with persistently heavy frost, overwintering a planted palm tree is only possible with relatively great effort. Wrapping and covering alone is not enough here. A temporary shelter, which you can build yourself from a few wooden posts and styrofoam, for example, can offer sufficient protection. It is particularly useful for specimens that are no higher than 2.40 m.
You need four sturdy wooden posts, which are driven into the ground around the palm tree. The easiest way to do this is to sharpen them beforehand. The upper ends are connected with boards of appropriate length. Rigid foam panels (Styrofoam or Styrodur) are then screwed to this framework. The slab on the roof is laid loosely and weighed down with stones or something similar. If you use commercially available wing screws to fasten the panels, especially on the south side, they can be loosened more easily if you want to open the construction a bit and ventilate the whole thing when the weather is nice.
Tip: No matter what type of winter protection it is, as soon as frost is no longer expected, it should be removed immediately. Otherwise, fungus and rot can occur under the cover.