In this article I hope to give a guide to the main options and problems of covering with some practical advice on designing and building covers.
WHY COVER AT ALL?
The most basic reasons are to protect developing blooms from wind
and rain, covers will also keep a lot of airbourne dust and dirt
from the flowers. Covers can also have an effect on the form,
colour and size of blooms (often but not always beneficial). Many
cactus and semi-cactus varieties e.g. the Athalie family and Kiwi
Gloria are totally different in character when covered being far
less chunky and more refined. Colours may be less intense under
cover but you may eliminate bleaching, fading and colour loss
found on outside grown blooms making for easier matching. The
grower also has more control over water supply, feed levels and
therefore ripeness. Last but not least the grower stays dry when
working on the plot.
In 1992 I grew about 900 exhibition plants of these all but 100
were covered. 650 under polythene and 150 under netting, the remaining
100 mainly miniatures and some 2nd and 3rd year seedlings were
uncovered and gave a very poor return. I got hammered out of sight
at one show needing a miniature ball for the championship when
I struggled to get a vase from 16 plants in full flush most being
battered and bruised by wind and rain despite a decent windbreak
to the west. It looks as though the miniatures may have to go
under cover now.
Disadvantages of covering can be increased plant height especially
by late in the season, reduced stem strength, colour loss and
banding with some varieties and especially under very hot conditions.
High temperatures, high humidity, condensation and other water
from leaks dripping onto blooms causing marking and spotting.
Some varieties just don’t like being covered.
Seasons all vary, sometimes covering is little if any advantage
but I reckon to cover as much as I can aiming to cover 10 to 12
days before the first important show I am aiming for. Odd early
blooms I’m afraid just take their chance outside.
DESIGN AND LAYOUT
On the new plots I opted for covers 16 feet wide which gives room
for three beds of plants 2 rows wide and 2 paths under each. The
gable ends face almost due east and west giving full exposure
to the prevailing westerly winds but also catching any slight
breeze on a hot day to run north and south and it was noticeable
how much more condensation and damping there was under these two
covers. To make best use of space these were 18 feet wide giving
2 paths, 2 beds of 2 rows and a central bed of 3 rows across the
width. Awkward to work and I’ve had problems shading the
outside beds if a tall variety goes in the middle bed.
Paths at cover eaves edges get very wet, most of mine are now
flagged or concreted. As I am at the top of the site most of the
water is donated to other plots. The first paths were just on
two feet wide, just right for a barrow but not for the knuckles
of anyone pushing the thing between the posts. These posts have
been called all sorts of things since they went in. Mark two covers
had 2.5 foot paths between them which are just right.
Build the covers as high as you think you can get away with, wives,
neighbours and allotment committees permitting. Our allotment
rules prohibit buildings or erections over 2.75 feet high without
the council’s consent. One is more a problem than the other
and what a funny height to pick.
My rogue covers sneak in at about 6.5 feet to the eaves and 8.5
to 9 feet to the ridge. I did talk to the people living round
the plots before I started and had no hassle. These heights mean
few concerns about the taller grower. no banging heads and good
air movement between the blooms and the tops.
THE FRAMEWORK
Tubular metal offers a strong support enabling big areas to be
sheeted and with the sheeting being held taut by being weighted
down or lashed on. In theory it will give in the wind and not
tear just riding over the framework, but if it rips the whole
plot can be devastated so I am wary. Angle iron or Dexion type
frameworks are also common but fixing can be awkward.
I’m happier with a hammer than a spanner so I’ve opted
for timber 3”x3” uprights at 3 metre centres support
the ridge and eaves rails on all covers. The ridge and eaves rails
are also 3”x3” timber. Uprights and rails are joined
using galvanised predrilled plates which builder’s merchants
stock for piecing up roof trusses and the like. There are 2”x2”
spars between the ridge and eaves at roughly 3’ centres.
I started with new timber, I’d recommend getting timbers
pressure impregnated with preservatives, firms normally charge
10-15% over normal cost for this service.
Smaller cover frameworks can use smaller section timbers or lighter
metalwork but don’t skimp and consider the shorter useful
life through rusting or rotting of lighter uprights. Getting the
whole lot level and square is vital if your sheeting or other
cover is ever going to fit and be reasonably taut.
I’m hoping my framework will see out my interest in showing.
When they fall down I will take the hint and pack up too but I’m
not planning on packing up yet so I’ve five gallons of Cuprinol
to go on this time and aim to do post bases every second season.
COVERTOPS
The cheapest suitable material I’ve found is 1000 gauge (syn
250mu) builders polythene which must be clear not tinted, this
is about 40 pounds per 25 metre x 4 metre roll (80’x13’
in real money). This is lathed down along the eaves and about
4.5 feet up each of the roof spars. At the end of the season it’s
rolled back to one of the eave rails and covered with black polythene
to stop it going brittle. Next time when it is rolled out again
you hit the same line of holes over the spars and eave rails preventing
leaks and dripping. The first three covers had a life of four
seasons, I’ve stripped it off this winter. Other options
are eyeletted sheets e.g. Toptarps which can be of 1500 gauge
and reinforced sheeting like Novaflex T. Woven polypropylene tarpaulin
sheeting seems very popular. I think you loose too much light
and I don’t like big flapping sheets which will belly easily
in heavy rain and which flick a lot of condensation onto flowers.
With all of these flexible sheeting covers I think you are asking
for problems with a roof slope of less than one in four.
Polythene covered framelights are widely used, I did all of the
old plots with that for 7 or 8 years. They took a lot of space
to store and a fair bit of work to recover a portion every season.
It took several days to get them up against about six hours to
put up my present ones up. So, overall I wasn’t sorry to
see them go.
Corrugated pvc would be nice but I am not as rich as the chrysanth
boys so I just admire theirs. Great for a neat small cover in
a back garden though and useful to make temporary frames/windbreaks
early in the season.
Whatever system you use you need a decent overhang on edges and
paths to stop blooms getting dripped on. On mine an 18 inch flap
of polythene hangs from the eaves, the free edges are attached
to laths which are then nailed together giving a “V”
shaped gutter between eaves. A 3 inch pvc gutter below the frames
is planned as a trial to keep paths and grower drier next year.
Muslin tents beneath the covers I believe reduce damping on soft
petalled varieties but they are awkward to cut blooms under and
it’s another job to cram into the busy pre-show work.
SIDE PROTECTION
The top cover will only keep off rain falling vertically in calm
conditions, a bit of a rarity in September but some growers never
learn! Top covers only in a gale with driving rain is probably
worse than nothing due to the wind funnelling and swirling effects.
Rokolene netting forms the basis of side protection. On most covers
I’d use a double layer secured to the frame at eaves level
and sandwiched between 3”xl” timbers at the bottom near
ground level. These can be rolled up or down depending on what
the weather is doing during the growing and flowering season.
I also use a lot of hessian, I’ve never bought any though
it’s always just appeared free. Don’t plant anything
other than strong stemmed whites or yellow varieties next to side
protection or colour loss or brewers droop can be a problem due
to shading.
NETITING COVERS
Over the last two seasons I’ve covered some varieties with
netting over the frameworks picking varieties I feel don’t
do well under polythene cover e.g. Paul and Linda’s Chester,
Senzoe Ursula and the Keenes. Hansonet, a very lightweight translucent
netting works well saving plants from the worst of the gales and
breaking even heavy rain to a fine mist. Agrofleece or Papronet
would probably work as well but cost more. If I was starting again
I’d build a netting cover framework much lower than the rest
as it’s awkward to handle a nine foot high cover.
JOKES AND FICTION
You are by now probably chomping at the bit waiting for advice
on covering tomato trays with plastic. Finding out all about rail
and bus company lost property sales to collect all of those commuters
brollies not to mention how to enliven an otherwise boring wasted
winter night by getting the whole family involved in making wire
frameworks and sewing all your old boxer shorts, sheets and fertilizer
sacks together to make those lovely tasteful cones for your giants.
Well it’s confession time I can offer no real help but I
have often thought the giants should be shown under the cones
with some sort of health warning on them. My only experience of
temporary covers were some 4’x4’ polythene framelights
nailed through onto 2”x2” uprights. They had the disconcerting
habit of nipping off on jaunts around the plots themselves from
time to time. So I will leave portable covers firmly to our southern
exhibitors. A few cans and a good Indian take-away fills in the
odd winter’s night for me with the odd catnapped dream of
the Klondyke for the 5th year.