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Last updated 19/12/2008

Sixty six Chempaks in a 16x8

By Paul Barlow

I guess there aren’t too many places in the U.K. where Chempak Roses are grown and flowered under glass, however in Aberdeen I’ve managed to do just that for five or six years now (but then I am a bit closer to the Arctic Circle than most other growers!) Last year I flowered 22 plants each of Chempak Rose and purple and red sports in my 16ftx8ft greenhouse.  This article covers my growing methods in general and my 2007 season with Chempak Rose and sports.

Taking Cuttings
Invariably I get Chempaks on the show bench in the second half of September, in 2007 I decided to try to get some flowers for the first half of the month. Cuttings were taken in two batches on 21st and 28th of November 2006. The compost used was Levingtons multipurpose mixed with perlite (3 parts compost to one part perlite).

I mainly use two types of container when propagating my cuttings – 84 cell plug trays (12x7) which gives me a fairly large sized cell, and standard seed trays into which I put up to 40 cuttings depending on cultivar and number of cuttings to be taken.  

Before inserting cuttings the compost is thoroughly watered and then sprinkled with a layer of perlite.

Cuttings are snapped to length and lower leaves removed before being dipped in hormone rooting powder and inserted into the compost.  When the required number of cuttings is taken the tray is watered again and then placed on the  bench in a cold part of the greenhouse for 7-10 days. Only after this cold period are trays transferred to the propagator at appx 55F bottom heat. Fourteen days later all cuttings are rooted.

Why a cold period for the cuttings? The late Jim Innes from Fraserburgh promoted this idea; Jim’s view was that the cutting needs to form a callus before roots can develop and callus formation can occur equally well without a heat source. One thing is clear, the method works and very few cuttings fail to root.

Potting on to first stage
When rooted cuttings are taken from the propagator they are left for about one week to acclimatise in a cooler part of the greenhouse. For the first stage of potting on I made a change in compost for 2007 – sticking with Levington Multipurpose but this time adding John Innes no2 in the ratio three parts Levington to one part JI2. This is a very convenient mix because Levington comes in 75 litre bags and JI2 in 25 litre bags – combining one bag of each gives the ratio I’m looking for.

Containers used at this stage can be either standard seed trays (12 plants to a tray) or 3˝” pots. Is there a difference in the end result? Hard to tell really – when moving plants to the next size container plants grown in the seed tray appear to have a more expansive root system than those in pots. Whether this is actually the case is debateable since the root system in the pot may actually be similar but it’s been constrained by the size of the pot. Certainly what I see above soil level is very similar from both methods.

This is normally the time when I use a growth retardant to keep the plants short and stocky prior to stopping. I find most cultivars will produce a good crop of even breaks when the leaf joints are close together. Application of the growth retardant three to four weeks before the stop helps to achieve this.

Potting on to second stage
After approximately five weeks in the small containers my plants are moved into individual pots. Depending on cultivar vigour and length of time each plant will be in the next pot I use either 5” pots or l˝ litre pots. Plants may be in these containers up to six weeks so a liquid feed is given towards the end of the period to keep them moving.

Most cultivars are moved from the greenhouse into the cold frame for a few weeks prior to planting out, but the Chempaks remain under glass since that would be their final planting position.

All Chempaks were stopped while in the second stage containers; dates for stopping were 12th March for the first batch and 19th March for the second batch.

I did drop a bit of a clanger at this point. Towards the end of April the plants were well advanced with laterals 15-18 inches in length. I was concerned that ultimate flowering height might exceed the height of the eaves of my greenhouse so I decided to spray the laterals with growth retardant. 

Only much later, as blooms were developing, did I realise this was not such a good idea. (See 2007 Conclusions).

Soil analysis and base dressing to Machin start point
I’ve long been a fan of soil analysis. Every year in early March I send soil samples from my greenhouses and the outdoor beds for analysis. The results are eagerly awaited. One common problem in Aberdeen is low pH and invariably I have to apply lime every other year. Ideally I would like a pH slightly higher than 6.5 at the start of the season, this will allow for a slight drop as the season progresses and still be close to 6.5 at the end.

Soil analysis results for my greenhouse for March 2007 were

N – 25ppm    P – 30ppm    K – 360ppm  Mg – 210ppm  pH– 6.6

Soil Conductivity – 310 microseimens/cm

Based on the analysis results I calculated the required base dressings to raise the nutrient level where necessary to that recommended by Barrie Machin, i.e.

N – 175ppm   P – 50ppm    K – 200ppm  Mg – 170ppm  

Base dressing takes place about ten days before planting; lime application (if required) takes place at least 4 weeks prior to base dressing.

As you can see from the analysis results only Nitrogen and Phosphate required attention. 

Planting out distances and system used
For years I’ve planted out in rows of two down each side of the central path in the greenhouse. In 2006 I experimented with one batch of Red Chempak Rose and planted out using a ‘domino five’ system.  Plants were positioned such that the breaks in the back row of plants (furthest away from the greenhouse path) ran parallel with the path, while the breaks on plants in the front and centre rows were set at 90 degrees to the greenhouse path. This meant I could still get easy access to the plants in the back row. The experiment was successful, both plants and blooms had adequate spacing and so in 2007 all Chempaks followed the ‘domino five’ system.

How did I arrive at 66 plants? I originally planned for 60 plants, 20 of each cultivar in two batches of 10. But like most of us, when I want 10 plants I will have 12 to choose from, and being reluctant to discard good plants I found I could put in another six plants with no noticeable compromise on spacing. 

Planting out usually takes place during the first week of May and 2007 was no exception. Of course planting under glass does not carry the same frost risk as planting outdoors. All Chempaks were reduced to two breaks by the end of the second week in May.

Summer jobs
Feeding commenced towards the end of May 2007. Initially a nitrogen only feed based on Nitrate chalk or sulphate of ammonia, 200ppm is my standard feed strength. Unfortunately summer 2007, as we all know, was dreadful, endless rain, dull days, very little sunshine etc. Under these conditions I reverted to Vitafeeds 1-0-1 and 3-0-1 to ensure adequate potash while still providing 200ppm nitrogen.

Feeding continued every five to seven days right through until late July and calyx split.

Spraying at this stage, was as always, carried out on an “as needed” basis. I know many areas had real problems with white rust in 2007, fortunately in Aberdeen this problem did not occur and to my knowledge no grower in Aberdeen or further north was troubled by white rust. The products I use are ‘off the shelf’ garden centre regulars – Systhane, Bug Clear, Fungus Clear, Rose Clear 3 etc.

Tying in the flowering laterals takes place every time I go down my garden. Whenever the growing tip of a lateral is more than 12 inches above the support ring I move the ring up another four to six inches; I find that one support ring is sufficient to keep each lateral securely attached to it’s cane. This is especially true with Chempaks given that they are well protected from wind and rain inside the confines of my greenhouse. 

Around early June I remove the top row of glass along both sides of my greenhouse, even in Aberdeen it can get quite hot under glass so partial glass removal is one way to keep the temperature down.

Buds were secured at the end of June through the first week of July. At this stage my spraying programme is stepped up a bit to ensure buds remain free from pests as they develop, once again, Garden Centre products are used.

As buds develop and calyx split approaches I apply the first of three layers of shading. Layer one consists of cool glass applied to the roof glass on both sides, then the end of the greenhouse and lastly the remaining glass on the west side of the house. The second layer is internal and is a curtain of rokolene netting which can be raised or lowered on wire runners attached from the apex of the greenhouse to the top of each vertical support along the sides of the greenhouse.

The final level of shading consists of a muslin or fleece tent erected above the area where the blooms will develop.

The last element in protecting the blooms is to put polythene in place of the row of glass that was removed earlier. The polythene is not the same size as the original glass so this allows air movement above and below the polythene while preventing the entry of driving rain.


I know this sounds like a lot of shading, and you may expect to see some colour loss when blooms reach maturity, but if this does happen it is so small that my blooms are not distinguishable from those of other growers on the show bench – leastways not for colour!

Bud and Bloom protection
In general, no bags are used with Chempak Rose and sports. If there are some early buds then I may bud bag them but once the majority of buds reach calyx split I abandon the bud bags and rely on regular visual checks for earwigs, slugs, snails and aphids. This often means going into the greenhouse after dark armed with a torch, as this is the most likely time to catch the larger of these pests. Of course this method is not foolproof and there have been occasions when entering the greenhouse first thing in the morning that I’ve been greeted with the presence of a few chewed petals around the base of the odd plant.

Show time
The first blooms of Chempak Rose and Red sport were shown at Aberdeen Royal Horticultural Society Show on 26th August. Showing continued through to the Naturally Fife Show on 15th September. This means my two batches of each cultivar covered three elapsed weeks of the early part of the Show season, and over 50% of available blooms were used in my exhibits. In 2007 only Joyce Frieda, Billy Bell and John Wingfield provided me with more blooms on the show bench than Chempak Rose and sports.

Chempak Rose (Best Vase) and Red Chempak included in 4x5 entry at Dundee Flower show Red and Purple Chempak included in 6x5 entry at Scottish National

Faults with Chempaks – yes of course there are a few – no cultivar is 100% perfect. Shallow and one-sided blooms are quite common; even what appears to be a level bud may eventually produce a slightly one-sided bloom. Neck extension between top leaf and bloom is in many cases too short and some leaves have to be removed to allow petals to fall naturally and unimpeded. 

Conclusions from 2007
Using growth retardant on flowering laterals was a mistake. In cultivars that already have a problem with neck extension and distance between leaf joints, I just compounded the problem. This resulted in having to remove more leaves than expected to allow blooms to develop unimpeded and even shorter leaf joints on the top half of each lateral which generally made plants more difficult to handle when tying in etc.

Do feed heavily – I think my 2007 plants could have withstood heavier feeding during the summer period giving the potential of better blooms. This is something to think out in 2008, especially after reading Ian Rankine’s article in the 2007 Year Book.

When space is at a premium the ‘domino five’ planting system works well, plants and blooms were adequately spaced. Although I’m not sure this would be the case for blooms that require bagging throughout their development as reaching through to the back row to put bags in place may prove a bit difficult.

My stopping dates were a bit too early in 2007; I know I wanted earlier blooms but not necessarily in August. I think the earlier stop, combined with a very warm bright spring, produced much faster early growth and ultimately lead to blooms sooner than expected.

Having had Chempak blooms in early September and late September in recent years I’m tempted to conclude that in 2007 my earlier blooms were smaller and shallower than the later blooms of previous years.

Summary of Activities        - Chempak Roses 2007 season
Cuttings inserted                - 21st and 28th November 2006
Potting on 3˝” pots/trays    - 3rd and 8th January 
Potting on 1˝ litre pots       - 4th and 8th March 
Stopping dates                   - 12th and 19th March 
Planting out                       - 1st May
First Buds visible                 - 17th June onwards 
Buds secured                      - 28th June to 6th July
Calyx split                          - 21st July to 8th August
Full bloom                          - 26th August to 15th September
Average leaf count              - 37-40 per flowering lateral

Page updated: 19 December, 2008  

 This article was first published in the National Chrysanthemum Society Yearbook, 2008. - bringing chrysanthemums to life!
© Copyright 2002 Paul Barlow.