| ANOTHER PERSPECTIVE |
ON COLD FRAMES |
By Porter Quesenberry & Lyle Graham, Life long gardeners, living
on their farms in Giles County and on Peter's Mountain.
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Growing in a Cold Frame
Use two by sixes, two by eights, two by tens, or two by twelves to construct
the sides
of the cold frame. Again, don't go to any expense in obtaining these
materials. If you
don't have them on hand you can use second grade lumber or pick up
some old
lumber at a salvage yard. Build the cold frame so it is higher in the
back and lower in
the front. Ideal dimensions would be approximately eighteen inches
at the back and
twelve at the front. This provides a slope for excessive rain to drain
off and fl better
angle for sun exposure.
You can either set the cold frame on top of the ground or bury it in
the ground. You
will find you will get better insulation if it is at least partially
below ground level. Any
wood that is placed in the ground should be treated with a wood preservative
otherwise it is apt to rot quite rapidly.
One of the major factors in building a cold frame is its placement in
the garden.
Whenever possible, the cold frame should face to the South for maximum
sunlight
exposure and it should face at an eight to ten percent angle for maximum
sunlight
exposure. If a southern exposure is not available the second choice
would be a
western exposure. Third choice would be an eastern exposure and the
least desirable
would be the northern exposure because of the lack of sufficient light.
When you place
a cold frame in the garden select a location with a slight slope, if
possible, to provide
adequate drainage.
Take time to properly prepare the soil in the cold frame to a depth
of at least eight to
twelve inches. A good fertile soil can be obtained by mixing compost,
peat moss, leaf
mold or other such additives with your existing soil. You may find
it necessary to
renew the soil every year or two, depending on fertility.
During cold winter weather it is important to cover the cold frame with
old burlap
bags, old blankets, or any type of cloth material to provide added
protection during a
cold spell. Once a cold spell has subsided the covering material should
be removed.
Another way to provide added protection during cold spells is to include
a heating
cable, submerged in the soil, in your cold frame. Heating cables not
only provide
additional winter protection for your winter vegetable crops, but they
also encourage
faster root development and are a special advantage if you are growing
seedlings, or
cuttings in the cold frame.
On a warm sunny day, during the fall, winter or early spring, it will
be necessary to
open the window sash for ventilation. You can use a stick, wedge, or
any similar
material to prop it open. Also, during warm weather it may be necessary
to cover the;
window sash with a netting, shade saran, or treat the glass with a
lime solution to
provide additional shade for your plants. This is especially important
during the warm
summer season.
You will have to experiment a little to determine how frequently to
water your cold
frame because the watering requirements will vary from day to day and
season to
season. Generally, during the winter season the cold frame will only
need to be
watered about once a week. Or, you can let Mother Nature do the job
by opening
the top of your cold frame on a rainy day.
One of the finest vegetables to grow in the fall and winter is leaf
lettuce. It grows
rapidly and abundantly in a cold frame. To speed up the crop the use
of a heating
cable in the soil is very beneficial. Other crops that grow well in
cold frames are
radishes, green onions and spinach. Try experimenting you will find
that it will only
take a portion of the cold frame to grow sufficient quantities of lettuce
or other crops
for your family. It is a good practice to devote only a portion of
the cold frame to a
single crop, using the remaining space to grow other vegetables for
winter use.
In addition to growing vegetables, a cold frame is an excellent place
to start new
seeds in springtime or to take cuttings in the fall and winter months
of your favorite
evergreen plants. In fact, the propagation of new plants, including
rhododendrons,
camellias, azaleas and other broad-leafed and conifer evergreens, can
take place in a
cold frame now. The cuttings can be taken any time from now until early
February.
You will find the cuttings will root better with bottom heat from the
submerged heating
cable. If you want to cut costs this winter and grow some of your own
produce, now
would be an excellent time to build a cold frame. It’s an easy project
and can save
you a lot of money.
Building and Using Hotbeds and Coldframes
A coldframe is a protected plant bed. It has no artificial heat added.
The temperature difference between the inside and outside of the frame
is generally not more than 5 to 10 degrees. A mat or blanket may be placed
over the frame on cold nights to conserve heat, but this increases temperature
by only a few degrees. There are times, however, when a few degrees can
be very important.
A coldframe is used to provide shelter for tender perennials,
to "harden off" seedling plants or to start cold-tolerant plants such as
pansies, cabbage or lettuce earlier than they can be started in open soil.
It may also be used to overwinter summer-rooted cuttings of woody plants.
A hotbed basically is a heated coldframe. In many ways it is a
miniature greenhouse, providing the same benefits with limited space at
minimal expense. It is a means for extending the growing season. It is
most often used to give an early start to warm-season vegetables such as
tomato, pepper or melon. It may also be used to root cuttings of some woody
plants.
Location
Hotbeds and coldframes should have a southern exposure to receive the maximum
amount of sunlight. To reduce the cost of heating, use a north or northwest
windbreak. This may be provided by a building, bales of hay or straw, tight
board fence or evergreen hedge. Bundles or bales of straw could be used
on the north for temporary windbreak. Windbreaks should not shade the
bed.
The site should have good natural drainage so there will not be
excess moisture beneath the bed. If the hotbed is below ground level, excellent
drainage is essential to keep water from entering or accumulating during
heavy rains. If natural drainage is not good, use drainage tile or a thick
layer of coarse gravel. If this is not practical, beds may also be built
above ground level for proper drainage. However, there will be greater
heat loss.
Locate beds near the house where they can be given frequent attention.
A convenient water supply should be available. If the structure is to be
heated electrically, have outlets close by.
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Constructing the bed
Basically, the hotbed or coldframe is a rectangular box with the back higher
than the front, covered with a transparent roof. The size and complexity
of the structure depend on needs or funds available. Often scrap lumber
and old window sash may be used, thereby reducing costs.
Sash and coverings. The sash available will determine the
dimensions for the bed. Glass sash is the conventional frame covering and
generally the best. Standard glass sash for coldframes and hotbeds is 3
feet by 6 feet. When this is used, the bed should be about 5 feet 8 inches
(front to back) by 3 feet or a multiple of 3 (6, 9, 12, 15 or more feet).
Used window sash is satisfactory and less expensive, but the frame
dimensions may have to be adjusted. Remember, whatever the size, the
slope from back to front should be 1 inch per foot.
If glass sash is not available or considered too expensive, the
frame may be covered with clear polyethylene (4 or 6 mil) stretched on
wooden frames. Polyethylene is lightweight and allows construction of many
sizes of simple frames. Such frames are lightweight and must be hinged
or hooked down to prevent lifting during strong winds.
Polyethylene films must be replaced yearly. Plastics lose heat
rapidly; a double layer with air space between improves heat retention.
Fiberglass may also be used as a covering. Use clear rather than
colored sheets for better light transmittance.
Materials. The sides of the structure may be wood, brick,
masonry blocks, concrete or metal. Masonry block, concrete or brick make
excellent permanent structures but are more costly than wood. Metal must
be well insulated, or heat loss is high.
The average home garden hotbed or coldframe is constructed of
wood. It is easy to work with and more temporary, but also more flexible
if the bed needs to be enlarged or removed as needs and interests change.
For longest durability, lumber should be treated with a preservative that
is not toxic to plants. Lumber that has been CCA pressure treated is suitable
for this use. Don't use wood treated with creosote or pentachlorophenol;
accumulation of fumes from these materials in a closed frame can cause
plant damage. Redwood and cedar are long-lasting woods.
If untreated wood is used, the frame can be painted with a white
latex-base paint or white greenhouse paint for added light reflectiveness
and protection.
One-inch-thick lumber may be used for the frame, but 2-inch has
greater durability and insulating qualities. The back wall (generally the
north wall) should be at least 18 inches tall, measuring from the top of
the heat source. The front wall (generally the south wall) should be about
12 inches tall for a 6-foot frame. Weather stripping at joints helps retain
heat and makes the frame more efficient. Use 2 x 4 lumber for corner posts
(see Figure 1).
Figure 1. General structure of a newly
built frame.(Illustration courtesy Lyle Graham)
Preparing the bed area. The area for the bed must be leveled.
Although temporary frames may be set on the soil surface, excavation is
required for more permanent structures. Most home hotbeds are heated with
electric coils, but where fresh manure is available, it may be used. A
deeper excavation is generally required for establishing a manure-heated
bed.
For electric heating, and where some drainage material is required,
excavate to a depth of about 14 inches. Corner posts should extend to the
base of the excavated area, but side walls need only be extended a few
inches below the level of the heat cables.
After the bed area has been excavated, place in it a layer of
coarse gravel about 6 inches deep. Cover the gravel layer with screening
or burlap to prevent sand and soil from sifting down into it. On this,
place a 2-inch layer of sand. Sand makes leveling easy and provides a base
for the heat coils. Remember that the 12-inch front and 18-inch back are
measured from the level of the heating cables. At this point the bed is
ready for laying the heating cable.
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Heating the hotbed
Methods for heating the beds include manure, electric cables, light bulbs,
hot water and steam. Manure-heated beds or of interest as a means of conserving
energy. Temperature control in manure-heated beds is more difficult than
in electric, and therefore, we can normally expect to grow better plants
in electrically heated beds. The manure-heated bed is suitable for only
short periods in either spring or fall. The electrically heated bed can
be used for any time period or even throughout the entire winter.
Manure. In areas where fresh manure is available, it is
a cheap and convenient heat source. Temporary hotbeds have been made by
simply placing the board frames on top of a flat pile of manure 8 or 9
feet wide and 18 to 24 inches deep. Additional manure is banked around
the sides of the frame for insulation and heat retention (see Figure 2).
Figure 2. Structure of hotbed built on
a pile of manure. (Illustration courtesy Lyle Graham)
Since this method requires large quantities of manure, it is not
generally practical. Heat can be used from smaller amounts of manure packed
in a pit beneath the frame.
The manure-heated hotbed provides a means for starting plants
several weeks earlier in the spring than they could be started outdoors.
It is built exactly like any other frame except that the pit beneath is
made 18 to 30 inches deep to hold the manure. Excellent drainage is
needed. If the manure layer becomes soaked with water, fermentation
stops and no heat is produced. Fresh horse manure containing about one-third
straw is excellent, but other manures may be used.
To prepare for the manure-heated bed, collect the manure into
a pile about 10 days before the bed is to be started. Compact and allow
to remain until heat starts. Then repile, compact and allow it to remain
undisturbed until heat is emitted for a second time. At that time, the
manure will be ready to pack into the pit beneath the frame.
Place the 6-inch layer of coarse gravel, as previously described
if there are drainage problems, or run tile out of the pit to release any
water as it enters. Tamp down the manure so the total depth of manure is
12 to 18 inches. Be sure to pack edges and corners as well. Next, cover
the manure with a layer of good soil 4 to 6 inches deep (see Figure 3).
Allow to remain for several days. The soil temperature may reach well beyond
100 degrees F. Wait until soil temperature drops to about 85 degrees F
before planting seeds or moving in plants. Use a soil thermometer. If temperatures
start to rise, always open sash promptly.
Figure 3. Structure of hotbed built on
a pile of manure.( Illustration courtesy Lyle Graham)
Electric heating cables. Since most gardeners do not have
adequate amounts of fresh manure available, electric heating cables are
the most convenient and dependable means for heating the hotbed. Cables
covered with either lead or plastic give good results when used properly.
Cables vary in length and wattage rating. Some are 30, 60 or 120
feet long with about 6.7 watts per foot. Others are in lengths of 6, 12,
24, 36, 48 or 96 feet with about 3.5 watts per linear foot. Other combinations
of length and wattage may be available in some areas.
Cable is installed so as to produce a certain number of watts
per square foot of bed area. Generally, in milder climates, such as Missouri's
Bootheel, 10 watts per square foot of bed space is adequate. Throughout
the remainder of the state, 12 watts or more should be used per square
foot.
Lay the cable on loose, level soil or sand with the bed prepared
as previously described. Be careful not to damage the covering of the cable
when handling. Avoid kinks that could damage or break the cable, and don't
cross cable over itself. Never cut the cable to shorten its length.
The spacing between the loops of cable is important and determines
the number of watts that are supplied per square foot of bed. Use the following
formula to determine the spacing between loops:
Spacing (inches) = (12 x watts
per foot of cable) ÷ wattage required per sq. ft. of bed
To determine the watts per foot of cable, divide the total number of watts
for the cable by its length in feet.
Example: Spacing for a 400-watt cable 60 feet long to produce
10 watts per square foot of bed area would be:
Spacing = (12 x [400 ÷
60]) ÷ 10
= (12 x 6.7) ÷ 10
= 8 inches between loops
The factor used here is 12, but spacing can easily be estimated for 12
watts per square foot of bed area. The number of watts per foot of cable
(as 6.7 in the above) becomes the same as the spacing needed between loops
(which would be 6.7 inches in this case) when the number 12 is substituted
for 10 in the above formula.
If the heating cable is too long, use spacing slightly closer
than calculated, but always distribute the cable uniformly throughout the
bed. Irregular spacing makes temperature control difficult. Generally,
a 60-foot cable should heat about 36 square feet of bed area.
After the cable is positioned, cover with sand or fine soil. Over
this, place half-inch-mesh hardware cloth. The hardware cloth protects
the cable from damage when soil above it is being worked for planting.
Over this, add the layer of soil for planting.
Thermostats. A thermostat is necessary to maintain uniform
temperatures. Some cables have built-in thermostats that keep the soil
temperature close to 74 degrees F. For larger beds, a separate, adjustable
thermostat is best.
Thermostats in general use have an operating range between 30
and 120 degrees F. They have a remote temperature bulb that should be buried
beneath about an inch of soil midway between two loops at the center of
the bed. Don't allow the bulb to come in contact with the heat cable.
Other heating methods. Light bulbs are less expensive but
also less satisfactory as a heat source. However, they can provide a quick
and easy means of adding supplementary heat on frosty nights of early spring.
About four 25-watt bulbs should be adequate for a 3 x 6 foot frame if spaced
around the sides. Use waterproof wiring and sockets. If more heat becomes
necessary, these bulbs can easily be changed for larger wattage bulbs.
If ground-level basement windows are present, it may be possible
to build the frame outside such a window, which, when open, would provide
some supplemental heat from the heated basement. Hot water and steam systems
are normally useful only for large commercial hotbeds and are seldom used
for the average home hotbed. Soil piled around the outside of the frame
provides added insulation and heat retention.
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Operating the hotbed or coldframe
Regardless of the method of heating or type of construction used, the hotbed
or coldframe must have proper temperature control, ventilation and watering.
Temperature. A soil temperature in the hotbed between 70
and 75 degrees F is ideal for planting most seeds. In the manure-heated
bed, seeds may be sown while the soil is slightly warmer, but once seedlings
appear, good ventilation is necessary to keep the seedlings from becoming
soft and weak if temperatures are still high.
Once seeds have germinated, temperatures should be adjusted for
the type of plants involved. They can be divided into two groups: cool-season
and warm-season crops. The cool-season crops include those that require
a relatively low growing temperature. Plants in this category are lettuce,
onions, cabbage, broccoli, cauliflower, larkspur, pansy, bachelor button,
primula, snapdragon, sweet pea, stock and many perennial garden flowers
being started from seeds.
Crops requiring higher growing temperatures include tomato, pepper,
eggplant, sweet potato, muskmelon, watermelon, squash and cucumber, as
well as many annual garden flowers.
Regardless of the group, most seeds can be germinated in a soil
at about 70 degrees F. The warm-season crops germinate a little better
if the soil is about 75 degrees F, while the cool-season crops could be
kept at 65 degrees F. Where this differential is not possible, the 70-degree
temperature is a good compromise.
The more critical temperature period begins after seeds have germinated.
Now air temperature becomes more important. Cool-season plants prefer an
air temperature of 65 to 70 degrees F in the day, with 55 to 60 degrees
F in the night. These plants will not be hurt by slightly lower temperatures.
In spring it is not always possible to keep daytime temperatures this cool,
but pay attention to night temperatures, which are more critical.
Warm-temperature plants should be kept at air temperatures between
65 and 75 degrees F during the day and not be exposed to lower than 60
degrees F at night.
In the coldframe, little temperature control is possible. Covering
the glass with pads or straw on exceptionally cold nights with careful
daytime ventilation are the main methods for heat conservation and control.
Ventilation. When ventilating the hotbed or coldframe,
raise the sash on the side opposite that from which the wind is blowing.
This prevents wind burn on young, tender plants or lifting of the sash
by strong winds.
During extremely cold weather, provide extra protection and conserve
heat by covering the sash with mats or a layer of straw. These must be
removed when weather clears and temperatures rise. Glass must be cleaned
when straw is removed to provide maximum light transmittance.
On warm, sunny days the sash may be opened wide or totally removed.
A thermometer is the best guide to determine what width of opening will
allow proper air movement for good temperature control.
Coldframes are ventilated in about the same way as hotbeds. Since
they are solely dependent on natural heat absorbed during the day, it is
important to close the sash promptly in the late afternoon or evening
after there is no danger of excess temperature buildup.
Watering. Proper watering promotes good growth and prevents
disease buildup. Frames should not be widely opened for watering at any
time when the temperature outside is below freezing. Watering should be
done early enough in the day so that foliage dries before nightfall or
before the frames are tightly closed.
In general, little watering is necessary while plants are small
and temperatures are cool early in the season. As the season progresses,
plants become larger and temperatures higher, so frames must be opened
longer and wider. This means that frequency of watering must also be increased.
Always allow the soil surface to dry between waterings, but do
not allow wilting. Occasionally, after several cloudy days are followed
by bright, sunny days and higher temperatures, these tender plants will
wilt. This is not an indication that the plants need water unless the soil
is obviously dry. If the condition is severe, misting over the foliage
or providing temporary light shade may be beneficial.
Soil pasteurization. The hotbed or coldframe should contain
4 to 6 inches of good garden soil for growing the seedlings. Weed seeds,
insects and diseases are found in ordinary garden soil. Fumigation or soil
pasteurization are helpful in reducing problems and maintenance.
For small beds, bake soil in a 140 degree F oven for 30 minutes
before placing into the beds, or if this is not possible, hot water may
be poured on the bed to provide some pasteurization. Hot water is hard
on soil structure and must be done well in advance of planting so that
the soil can dry adequately and be worked well before planting.
In most cases it is more convenient to sow seeds in flats or pots,
which are then placed in the hotbed. In this case, the soil layer is not
essential and the flats or pots may be placed on the sand directly above
the coils. Pasteurization of individual units is also possible and easier.
Fertilization. There is generally no need for addition
of fertilizer in the seedbed preparation. If the fertility of the soil
is not known, it would be beneficial to have a soil test run and appropriate
additions made. After seeds have germinated and developed their first true
leaves, a light addition of liquid fertilizer should be made. This should
be repeated at about two-week intervals while the plants are in the frame.
Pests. Remember that your hotbed or coldframe contains
some of the most lush, soft plant growth available to insects in early
spring. They are attracted to it. Therefore, keep a close watch for pests
and apply appropriate controls before plants are seriously injured.
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Hardening plants
Plants started in a hotbed and especially those started indoors should
be "hardened" before they are moved into the garden. A coldframe is an
ideal place to accomplish this. The hotbed may also be used.
To harden the plants, gradually expose them to the sun and wind
first by keeping the sash open wider and longer each day as well as at
night if nights are not too cool. Gradually the length of time and amount
the sash is opened are extended until it is removed. However, be ready
to return the sash in case of a sudden late spring freeze.
Other uses
Hotbeds and particularly coldframes may be used to protect tender plants
during winter. Tender varieties of chrysanthemums, for example, may be
lifted after flowering and set into the coldframe to overwinter.
For other slightly tender perennial flowers, a portable coldframe
may be placed over the plants directly in the garden where they are growing.
The entire structure can then be removed in the spring. Plants that may
benefit from such protection in some areas include poppy anemone, foxtail
lily, hardy gloxinia, some lilies, oriental poppy and viola.
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FALL & WINTER PLANTING GUIDE
Fall and Winter gardening, although an old practice, is an excellent
solution for
keeping the tilth and fertility of your garden's soil at its peak levels.
At the same time it
yields crops of delicious vegetables throughout the fall and winter
that cost a fraction
of produce purchased in the supermarket.
Many southern areas of the U.S. are suited to winter crops, while some
of the more
northern and mountainous regions have to rely on cold frames, hot beds,
or greenhouses.
The key to successful winter gardening is knowing the average date of
the first killing
frost in your region (often early October in the mountains and valleys
of Southwest Virginia). You then plant your winter crops early enough to
let them reach their full maturity before that killing frost. Local garden
gurus can give you information about the timing of first frosts and the
hardiness of various crops for your area.
Late maturing crops - Approximate maturity 90 days. Plant by
mid July for fall
harvest, later for spring harvest.
ROOTCROPS
Beets
Carrots
Parsnip
Rutabaga
Globe Onions
LEAFCROPS
Brussells Sprouts
Cabbages
Cauliflower
Fava Bean
Mid-season crops - Approximate maturity 60 days. Plant by mid
August. Use
any of the dates from above as well as the Best Dates below.
ROOTCROPS
Early Carrots
Leek
Turnip
Kohlrabi
LEAFCROPS
Early Cabbages
Winter Cauliflower
Collards
Perennial Flowers
Perennial Herbs
Swiss Chard
Early maturing crops - Approximate maturity
30 days. Plant by mid
September. Use the dates from the previous page as well as the
Best Dates below.
The latest dates are for warmer climates, later
frosts, or protected plantings.
ROOTCROPS
Chives
Bunching Onions
Radishes
LEAFCROPS
Broccoli
Cover Crops
Leaf Lettuces
Mustard
Spinach
Lawn seed