The Architecture of Horticulture

People often say to me that January must be the worst time of year on the nursery, and that with the cold, wet weather and lack of plant growth, I must be counting down the days to Spring. Well for this propagator, January holds its own rewards and lends itself to being an interesting and varied time, so my reply of “I actually really enjoy the winter” is always met with puzzled looks.

The beauty of growing plants on the nursery is that the season doesn’t end. There are always plants in bloom even in the depths of winter and the work of a propagator in January is diverse and rewarding. This is all thanks to the architectural structures of the nursery – the glasshouses, cold frames and polytunnels that support growth and development even in the coldest climates.

Frames and Glass

Frames and Glass

The Glasshouse
The heart of the nursery is the main glasshouse. Built in the 1960’s, it encompasses two sections; a large growing on area and a smaller partitioned propagation area. The propagation area is heated to a temperature of 10˚C and is full to bursting in January. Seed sowing begins in earnest in October, so by now the benches are full with pricked out seedlings of various genus and species. Little gems currently growing on include Albuca shawii, Omphalodes linifolia and various species of eryngium. The heated seed frame is also full, with January being a particularly busy month for sowing a multitude of perennial seeds including oenothera, digitalis, delphiniums and lupins to name just a few.

The cuttings bench has been quiet for a couple of months now, but with its winter clean completed this week I was able to commence taking cuttings. There is very limited cutting material available from the garden at this time of year with perhaps a few hardwood cuttings possible, but it is the protected structures of the nursery which offer us a huge range of soft and semi-ripe plant material, perfect for vegetative cuttings. The ability to take cuttings this early in the season gives me a head start on producing plants for the garden to use during the coming spring and summer.

Yesterday I took nodal tip cuttings of Iberis gibralterica ‘Betty Swainson,’ a superb short lived perennial which blooms for an amazingly long period. This is a new plant for Sissinghurst, chosen by Troy, our head gardener, and with its pure white blooms it’s sure to make an elegant addition to the garden. Also on the cuttings bench was Salvia ‘Nachtvlinder’ a stunning perennial with dark purple flower spikes, introduced last year after Claire, one of our gardeners saw it at a plant fair. It proved to be striking in both pots and in the purple border. Other delights all taken as nodal tip cuttings included Othonna cheirfolia, Diascia personata, Maurandya barclayana ‘Alba’ and Pelargonium sidoides.



The main glasshouse (heated to an optimum temperature of 8˚C) currently holds our stock of Pelargonium ‘Lord Bute’. The plants have just been potted into their final 2 litre containers in the last couple of weeks and were propagated as semi-ripe, nodal tip cuttings back in August and September last year. Also taking centre stage is our crop of sweet peas. Grown from seed the sweet peas were sown in November last year and they are now about 20cms tall. In another few weeks we will pinch out the tops to encourage strong, bushy plants to develop. There are 12 different varieties, with some destined for the garden and other new varieties destined to be trialled on the nursery with a view to selecting the best for the garden’s use in 2016.  The rest will provide cut flowers for use around the property. Alongside these two crops are various mature seedlings which have now been potted on and will continue to grow on in the glasshouse for the next couple of months.

The Longhouse
The longhouse, as the name suggests, is a slim line glasshouse which runs the length of the office and workshop buildings, adjacent to the nursery. The longhouse is heated to stay frost free and is the winter home of the garden’s range of superb planted pots. It is also the source of some of the best colour on the nursery in the colder months of the year and a fantastic source of cuttings material. Claire is the person responsible for planting up and selecting the fascinating range of plants and her talent for creating the pots, is an important facet of the garden. The selection, placement and care of the pots adds a layer of interest and beauty to the garden which would be sorely missed if it wasn’t maintained.

An icy Long House

An icy Long House

Abutilon 'Nabob'

Abutilon ‘Nabob’

Currently flowering to their hearts content in the longhouse is the exquisite Tibouchina urvilleana, a tender shrub which bears stunningly beautiful, rich purple blooms. Visitors to the garden can see it adorning the courtyard steps in summer. I take cuttings from the main plant as and when I can as, because they flower so much, Tibouchina do not produce a huge amount of cutting material, so I have to take the opportunity when it presents itself, without causing detrimental effect to this important plant. Last year, I was able to build up a stock of about 15 young plants, one of which will be destined to be potted up by Claire as a replacement for the original plant. Other plants of interest in the longhouse include Alyogyne huegelii ‘Santa Cruz’ with its large saucer shaped blue flowers, various species of Salvia and excitingly our Punica granatum (Pomegranate) is currently bearing fruit.

The cold frames
The cold frames are the most traditional element of the nursery and we have 6 rows of frames with 3 frame units in each row, each unit is covered with 5 dutch lights and measures just under 3m in length and 1.2m in width.

Cold frames are a superb resource offering winter protection against cold temperatures and excessive wet. The frames work by creating a micro-climate around the plants, with the day’s sunlight heating the air and soil temperatures within the frame. The lights, which are open during the day, are then closed at night trapping the warmer environment and keeping temperatures several degrees higher than the colder outside conditions. The frames also offer protection against wind chill which takes heat and moisture from the plants and can potentially cause severe damage. Closing the frames when there is heavy rain prevents the plants from becoming excessively wet. Cold will do more damage to saturated root systems then it will to drier plants.

As well as protection, cold frames allow earlier growth and development of plants in spring. The temperature at which growth commences after the winter is in the region 6˚C, so plants in cold frames will reach this optimum temperature before their counterparts which have been outside over the winter months. On the nursery, we can utilise this advantage and use the cold frames to have plants ready for the gardeners to plant out earlier in the season. It also means that herbaceous perennials will begin growing earlier and this early growth makes superb cuttings which are called basal stem cuttings.

Basal stem cuttings are fantastic, as they root incredibly efficiently and with a very high degree of success. This is due to the fact that if material is collected properly, the cutting will have a piece of woody stem at the base which comes from the crown of the parent plant. This woody material is predisposed to easily produce roots and so dramatically increases the success of the cutting. When collecting basal stem cuttings look for healthy, fresh shoots and take time to ensure each cutting has a small section of woody material at its base. Depending on the weather, I will hopefully begin taking basal cuttings towards the end of next month. Delphiniums are one example of a plant which lends itself very well to this form of propagation.

Polytunnels may not have the aesthetic appeal of the glasshouses or the cold frames but they are incredibly valuable to the nursery in terms of winter protection and early growth in February and March. The polytunnels have all the protective capabilities of the cold frames and enable me to start off early batches of winter vulnerable plants such as Osteospermums and Argyranthemums and bring on the development of spring bulbs such as the striking Fritillaria imperialis ‘Rubra’.

The biggest advantage of polytunnels is that they are extremely efficient at retaining day time warmth and actually suffer less temperature fluctuation than an equivalent unheated glasshouse. This reduces temperature stresses on the plants and encourages them to begin growing earlier than plants outside. The biggest issue, however, is ventilation and even in January it is essential to open the doors at one end every day to prevent problems with fungal diseases.

Like the longhouse, the tunnel’s protection of the plants mean there is cutting material available even at this time of year and on the schedule for next week is propagation of santolinas, teucrium, penstemon and more.

In essence, January is a truly valuable time of year and if you are fortunate enough to have a protected structure to grow in, be it a glasshouse, polytunnel or cold frame don’t write January off. Embrace it and start your gardening year now.

Emma, propagator

7 thoughts on “The Architecture of Horticulture

  1. Hi Emma
    Is that Senicio viravira in the photo of cuttings? It was at Sissinhurst I first saw this plant in 1982.
    We grow it well here in New Zealand. I am frost free. Enjoyed your blog on January propagation.


    • Hi Rodja thank you for your question, yes it is Senecio viravira. Its a fantastic plant and one I particularly like due to the deeply cut foliage, its really interesting to know it was being grown here 1982. Really pleased you enjoyed the blog, best wishes Emma


  2. I bought a new cold frame last autumn and now it is full (and overflowing) with pots of seed that need a cold spell in order to germinate. I think I might have ordered too many!


    • Hi Andrew, theres nothing better than growing seeds which need cold to germinate, the sight of the seeds coming up in the spring is so satisfying and definately worth waiting for. Good luck with your cold frame and thanks reading our blog


  3. Pingback: Perto do apocalipse + | Quinta do Sargaçal

  4. Thanks, Emma. It is very interesting to see behind the scenes. As I sit here looking at a forecast of 38 for tomorrow (I live in Sydney), it is hard to believe your snow, but you have inspired me to try and track down Abutilon ‘Nabob’. What a stunning colour. Abutilons grow well in my garden (and, incidentally, tibouchinas are a common street tree here) and I’d love to add another.


    • Hi Janna thank you for your message. ‘Nabob’ is a truly beautiful variety of Abutilon and well worth tracking down, good luck in your search. The Tibouchinas in Sydney must be amazing, thanks again and all the best, Emma


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