EXTENDING THE SEASON

A: MULCHES

Mulches can be used alone or in combination with other equipment to raise the soil temperature, reduce competition from weeds and reduce moisture loss. Mulches are of several types. Both clear and black polyethylene have been used but not with equal results. Black is good for suppressing weed growth but is not as effective in raising soil temperature as clear poly. Both create a litter problem as they do not decompose and they must be gathered up for disposal. There are some biodegradable mulches available that are supposed to last for one season and should decompose by fall. In my own experience in the north, they do not last until harvest due to the long hours of sunlight in the summer. They decompose early in the season and become ineffective for weed control and moisture retention. Some books recommend organic mulches to control weeds but in the north they act as insulation and keep the soil too cool and inhibit good growth. During tests at Fort Chimo, Quebec in 1964-65, it was shown that a covering or mulch of organic matter kept the soil much cooler than either bare soil or soil under a grass cover. At a depth of 4" (10cm),the soil temperature was 59.6°F (15.3°C) for bare cultivated ground, and 65.2°F (18.4°C) for uncultivated ground but only 41.1°F (5°C) where a covering of sphagnum moss existed. Although moss has a low thermal conductivity rating when dry, it has a large capacity for absorbing and holding moisture. In daytime this moisture is lost rapidly and this results in a high heat loss as vaporization of water requires heat. The soil is cooling when it should be accumulating warmth. If organic mulches are used, they should not be applied until the soil has warmed sufficiently, at least July.

To increase the air temperature, many different methods have been developed. They range from individual plant covers to plant shelters that are temporary greenhouses. Individual covers may be as simple as a plastic bottle with its bottom cut out. The cap is opened and closed as necessary to control heat buildup. Many types of plant covers are available through nurseries and garden centres. They range from economical devices such as Hotkaps to one of the newest, the Igloo.

B: ROW COVERS

Row covers are another product that is widely available. They range from small plastic and poly units for $5 to models costing $40. In many cases the poly must be replaced yearly unless extreme care is taken in handling and storage. Some of these row covers have slit poly covers. These row covers are designed to provide ventilation to eliminate daily opening and closing of the poly. The frost protection from them is not as good as with solid covers. Only 28-29°F (-2°C) can be endured, therefore they should not be relied upon for protection from heavy frosts but should only be used for a 10 to 14 day headstart on the season.

By combining mulches with row covers, not only is the air temperature increased, but the soil temperature is higher than with either of them alone. This increase of between 6-8°F (3.3-4.5°C) can extend the season by weeks, and ensure a successful garden.

Unfortunately there is one crop that cannot be aided by row covers if cloudy, cool weather persists for an extended period of time. Vine crops tend to wilt when the sunny weather returns because the uptake of water was prevented by the cool soil temperatures that result from the extended cool weather.

C: HOTKAPS

Hotkaps come in several designs and sizes but esentially they are the same. They are made of treated paper, the larger sizes being supported by wire. They are set over the plant and soil used to hold them in place. The smaller ones, usually available in most catalogues and garden centres, are too small for all but the shortest of time. They are quickly outgrown. They are also very susceptible to crushing by the late snows common to the north. For ventilation, they must be torn open and this then makes them useless for frost protection. If frosts threaten, another cover will then have to be applied. Hotkaps give only 2-3 degrees of protection.

D: PLASTIC IGLOOS

The Plastic Igloo is a new development patented by a Toronto biologist. It is a plastic tetrahedron (3 sided pyramid), 18" tall (45.7cm) and filled with water. They are placed over the plants and the 4" layer of water acts as insulation even when it freezes. Experiments indicate that even when the outside temperature was as low as zero, Fahrenheit, the inside temperature never fell below 28°F (-2.2°C). This would provide a safe method of overwintering semi-hardy plant material as well. The only source of the Igloo that I know of at present is C. A. Cruikshank Inc. and they cost $2.60 each. They are reusable so the cost per year is not really that high compared to Hotkaps which are a one-time only product.

E: SUNHATS

Sunhats are another reusable product. They are cones of clear rigid plastic, 9 1/4" (23.5 cm) high. Green striping provides a shifting pattern of shade throughout the day. The plants are also protected from the hot sun by a moisture film on the inside of the sunhat. A hole in the top provides ventilation. They create a miniature greenhouse for the plant, protecting it from weather and insects while conserving moisture and increasing soil temperature. This increases the growth rate of the plant. Sunhats are one of my standard protectors. Their taller height makes them more desirable for taller plants than Hotkaps. If severe frosts threaten, the hole in the top can be covered with a small plastic bag, or poly thrown over the whole row. They cost $.80 each and more than save that much in a few years.

F: TOMATO HOODS

Tomato hoods or jackets are another product that finds regular use in my garden. They consist of a length of tubular plastic film with vent holes. It is cut to length and placed over the plant and stake. The top is gathered and secured to the stake. As the season progresses, the tube can be raised up higher on the stake. The film not only protects the plants from minor spring frosts, but it also retains warmth to aid in ripening the tomatoes. It is reusable with care and is relatively inexpensive. It costs $6 for enough film to cover from 6 to 10 plants. Besides its advantages in heat retention, it is excellent protection for the tomatoes from hail damage. It is only removed during periods of extreme heat and then it only has to be rolled up and secured to the stake. When the temperature cools, unroll it and it is back to work. The only problem I have had so far with the film is slugs. They tend to find the shelter of the hoods attractive and bait must be used to control them.

G: RUMSEY CLOCHE CLIPS

Rumsey Cloche Clips are an aid to making you own plant shelters. They are rubber and aluminum clips designed to hold two pieces of glass or plastic together in the form of a tent, thus creating a mini-greenhouse for the plant. They are very expensive, 6 for $8.95. I have seen them used to create a long solid row cover that is easily dissassembled. For this use, they can be put further apart and this will reduce the number needed.

H: PLANT CAPES

Plant Capes are a different type of plant protector. They are made of the same material as the Sunhats. They are a collar that is placed around the stem of the plant. They conserve moisture, increase soil temperature, and direct water to the roots of the plants. They reduce weeds and slug damage. They adjust as the plant grows. They are not for frost protection.

I: PORTABLE GREENHOUSES

Most catalogues list portable greenhouses and their prices range from approximately $200 to around $400 for most units depending upon size. There seems to be little difference in price from one company to the next for a similar greenhouse, although some charge shipping charges as well.

Gerard H. Gubbels, who was a horticulturist at Mile 1019 Experimental Farm when it was operational, wrote a pamphlet describing the construction and erection of portable crop shelters that can be made in sections and erected in the field. These are built to be dissassembled and stored from year to year.

J: COLD FRAMES AND HOT BEDS

Cold frames can range from inexpensive home built units to ready-to-assemble kits that tend to be very expensive. MacFayden lists a soft plastic cold frame for $35 to $40 and a solid one from $90 to $160. The booklet "Container Gardening" (Ag Canada pub. 1653) has plans for several different designs of cold frames which could be built economically and are much more efficient than the kits.

Hot beds are generally cold frames that have been heated by either biological methods or heating cables. The cheapest method of heating a hot bed is with manure. Raw manure generates considerable heat when it is decomposing. It is for this reason that it should never be used around plants until it is decomposed or well rotted. By putting this characteristic to use, many people get that extra early start on spring without the expense of a greenhouse. There are several drawbacks, though, to using raw manure. First is that it is odorous and this can create a problem in urban areas. Also, it is not always readily available.

One method of overcoming the problem of heating a hot bed is by the use of soil heating cables. These cables are similar to the ones used to melt snow off your eaves in the winter or to prevent your water lines from freezing. They are thermostatically controlled to provide the proper heat level that plant roots require. Plants can withstand lower air temperatures as long as the soil temperature is kept optimum. These cables are also useful for providing bottom heat to aid in seed germination.

Many of the devices mentioned in this section can be economically provided or created with a little ingenuity. The key is to make gardening enjoyable as well as rewarding by ensuring crop success.

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This page by Pat
updated August 18, 2000

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