Winter Growth

Is it better to encourage our palms to grow over the winter, or to allow them to rest? Alan Hindle discusses the pros and cons.
by Alan Hindle, 3 Wenlock Close, Sedgley, Dudley, West Midlands DY3 3NJ
Chamaerops No.37, Winter Edition 2000

Caryota sp. ”Himalaya” growing in Katmandu, Nepal.

As a relative newcomer to palm cultivation, my collection consists mainly of seedlings, which I would obviously like to grow to a plantable size as quickly as possible. My first batch of seedlings, purchased in 1996, consisted of Trachycarpus fortunei, Trachycarpus wagnerianus, Phoenix canariensis, Dypsis decaryi, Livistonia australis, Rhapis exelsa, Caryota rumphiana, and Butia capitata. I potted them up straight away into 10cm terracotta pots using a proprietary loam based compost and then placed them in our lean-to conservatory. Subsequently a green slime appeared around the outside of the pots indicating poor drainage. Only the two Trachys survived, which I believe was due to their more rootbound state and robust constitution. They are now about 40cm high and will soon require repotting for a fourth time.

Somewhat disillusioned by my lack of success, the following year I obtained large specimens of Chamaerops humilis and Yucca gloriosa (20-cm pots), which both went straight into the ground. The Chamaerops are protected from hard frosts with bubble wrap, and the Yucca, with its razor-sharp blue-green leaves, receives none. The latter is also starting to become quite large and is beginning to develop signs of a trunk. Later on I also purchased a Butia capitata of a reasonable size (12-cm pot), along with seedlings of Brahea armata and Chamaedorea radicalis.

In order to try and improve the drainage quality of my potting mixes I started off by adding sand and coarse gravel to my loam based John Innes 3 compost, but found this difficult to wet and slow draining. I now add perlite granules, grit, and some organic matter to a loam based or peat based compost (depending upon the plant’s acidity requirements). I also decided to stand the pots on saucers full of gravel in order to minimise the chances of plants being left standing in water. Also that year I pot-planted a cheap but fairly large Phoenix canariensis into a barrel planter along with half a dozen Pelargoniums. This attractive arrangement, placed outside our front door, is brought into the porch on frosty nights and moved under the carport during ground frosts.

In the spring of 1998, I ordered seedlings of Caryota ‚Himalaya,’ Rhopalostylis sapida, Sabal bermudana, Sabal palmetto, Trithrinax acanthocoma, Brahea edulis, and Jubaea chilensis. The Sabal palmetto, Trithrinax acanthocoma, and Brahea edulis were re-potted due to their more developed root systems. The Jubaea chilensis died inexplicably, something I have heard has happened to other EPS members. I would like to know what accounts for failure with Jubaea seedlings and the secrets for their successful cultivation. Are better results achieved by planting them straight into the ground?

That spring I also emptied my Pelargonium barrel to find that the Phoenix had sent roots down to cover the base of the barrel. While still in its plastic pot, I decided to transfer the Phoenix into the ground. I then bought a new one (along with some more Pelargoniums) to refill the barrel. The Phoenix in the ground is protected with bubble wrap when the temperature drops below 3° Celsius (as reported in my letter in Chamaerops 33). In the autumn I purchased seedlings of Sabal minor, Syagrus romanzoffiana, Trachycarpus latisectus, Trachycarpus martianus and a Trachycarpus fortunei of about 1.2m in height, which remains in its tub.

Later that year, in my eagerness to induce winter growth in my seedlings without the high costs of heating the whole conservatory, I proceeded to make a foolish mistake. I purchased a two-shelf cold frame with a removable transparent plastic cover, which also unzipped at the front. In this I placed many of my small seedlings together with a fan heater at the bottom, which was set to a minimum temperature of 16 Celsius.

Unfortunately, the dry air created by the fan heater, in such a confined space, had serious consequences for those seedlings which were either in the firing line or were more sensitive to low humidity. Of the casualties, my Sabals, Brahea armata, and Trithrinax were damaged but all recovered, whereas my Caryota ‚Himalaya‘ palms are still suffering. Caryota ‚Himalaya‘ is living on the edge, not helped by its mineral requirements; Trachycarpus martianus is now just about recovering but the dry air exacerbated its problems with red spider mites; and Trachycarpus latisectus is just a brown stump. At the conclusion of my experiment I must report that most of these seedlings are still in their original pots, and are no more advanced than when I bought them.

Late in the autumn of 1999, I received seedlings of Ceroxylon parvifrons, Dypsis decipiens, Jubaea chilensis, Livistonia jenkinsiana, Parajubaea cocoides, Phoenix reclinata, Phoenix rupicola, Sabal uresana, and Trithrinax campestris. Still adamant on maintaining winter growth and having read Paul Saunders’ article on the subject of over-wintering seedlings indoors (Chamaerops 34), I took advantage of the fact that we were renovating our front room and had removed the radiators. The room also has a large south-facing window, thus providing conditions of good light, no dry air, and cooler nights. The room’s temperature in the winter rises to around 18 Celsius in the daytime and drops to around 10 Celsius at night. I brought in those small seedlings, which were more likely to respond to the darker conditions and cooler temperatures (no Braheas or Sabals), together with my three Caryota ‚Himalaya‘ seedlings, which had suffered from the previous winter’s treatment. I hoped that this would at least keep them alive over the winter until the conservatory started to warm up again. Most of the seedlings have, so far, grown slowly throughout the winter, requiring more frequent watering compared with those plants that remain in the cold conditions of the conservatory. Unfortunately, the leaves of the Dypsis decipiens shrivelled one by one, leaving just an emergent spear, which was either due to the compost drying out or an attack of scale insect. I am hoping that it will recover in the conservatory this summer.
Overall, I am not sure that trying to encourage winter growth, rather than leaving the plants to enjoy a winter rest, is productive in the long term. Paul Saunders concluded that, although he had achieved quite good growth over the winter, in many cases he was a little disappointed with the lack of accelerated growth the following summer. I will be able to judge this in the autumn but am hoping that the fact that I have not administered any feed during the winter will at least have afforded the plants some rest. Maybe over-wintering indoors is best left for rainforest species rather than for the temperate palms which the majority of us EPS members prefer. This method may also be useful for nursing sick plants through the winter until more favourable conditions for recovery arrive.

I hope that my experiences may be of use to other new members who may be tempted to make the same mistakes. I am beginning to realise that palm growing is all about reproducing as closely as possible the growing conditions in a palm’s natural habitat, and having a good deal of patience along with it. Meanwhile, my latest batch of seedlings is an assortment of Trachycarpus species and a Chamaerops humilis var. cerifera, which spent the winter enjoying their cold rest in the conservatory.