Once the crop is in the ground or has emerged from dormancy and is started growing again, growers will often apply a cover to the soil. There are some general recommendations that are often given for their use. Each covering has a different purpose. The type, nature and purpose of the covering depends on the crop.
It is useful to take a look at some of the recommendations for the different covers that might be applied at this time of year, or that might have already been applied, and consider the reason or purpose behind each of them.
Straw
Straw is commonly applied to perennial crops such as strawberries and garlic.
Recommendation: 1-2 inches (2.5-5cm) of straw should be applied to Day-neutral strawberries once they have had a chance to establish following planting, typically in early June.
Purpose: Straw is used to create a clean barrier between the developing plants and fruit and the soil surface. Clean straw prevents soilborne pathogens from being splashed onto the fruit, reducing the incidence of diseases dramatically. The straw also conserves moisture and gives something clean for pickers to walk on later.
Recommendation: 4-6 inches of straw is applied to June-bearing strawberries in mid-October to mid-November each year. Straw is also recommended to be applied to garlic plantings if snow covers are inadequate.
Purpose: Straw provides an insulating layer, which protects strawberry plants from cold winter temperatures, as well as temperature fluctuations. When the straw is removed from the plants the following spring, it creates a clean barrier between the plants and the soil, reducing disease incidence.
For garlic, the straw protects the overwintering plants, as well as keeps soils cool in summer, conserving moisture and reducing moisture stress.
Row or Field Covers
Spun woven fabric covers of different weights, sizes and lengths are applied to annual or perennial crops at different times in the year. These covers may be put on once and left for an extended period, or may be put on and off, as required.
Recommendation: Apply a lightweight fabric cover to primocane (fall-bearing) raspberries in early spring.
Purpose: Research from back in the late 1990’s (but still good today) found that applying a fabric cover to a primocane planting boosted growth by a couple of weeks at least. The row or field covers create a warmer microclimate that gets plants going more quickly and increases growth.
Primocane fruit yield is entirely dependent on the length of the season. Each node that reaching the point where it switches from vegetative to generative equals more production.
Recommendation: Apply a lightweight fabric cover over some crops in spring, either as a row cover or field cover.
Purpose: For crops that respond to slightly hirer soil temperatures with more rapid germination and emergence, you can speed up crop growth and reach harvest maturity more quickly. Covers can also protect crops from slight early season frosts. As the
Purpose: Some crops benefit from the protection from attack by pests that is offered by the covers. Small, sensitive, direct-seeded crops such as radishes and various Cole crops can be protected from pests like flea beetles, cabbage maggots, etc. Either they outgrow the pest, being more able to bear the damage, or the pest cannot get close enough to lay eggs.
Recommendation: Apply row/field covers of various weights in late summer to late season crops such as day-neutral strawberries
Purpose: As the weight/thickness of the cover increases, the insulative potential of the cover increases. Laying out covers in fall can protect crops from frosts, allowing the crop to continue to produce for an extended period. By pulling off the covers after the danger of frost passes, the crop continues to grow and produce.
Fall-applied covers can also provide winter protection for some crops, in combination with a winter snow cover. These covers are used in a similar manner to straw (in some locations, they replace it), although will generally not provide the same level of insulation as that provided by straw.
Bark Mulch
Bark mulch (of different coarseness) is applied to different woody perennial crops.
Recommendation: Apply a layer of bark mulch in a strip to the base of orchard crops, such as Saskatoon berries in the spring. Typically, this is done in establishment years, but may be refreshed periodically.
Purpose: The bark mulch serves to reduce soil temperatures and conserve soil moisture for developing plants. This reduces irrigation requirements, in some cases removing the requirement entirely. The bark mulch can also slow or reduce weed growth somewhat.
Plastic Mulches
The use of plastic mulches is typical for many annual vegetable crops, particularly those that are transplanted. Mulches may also be used for some orchard and nursery crops.
Recommendation: Apply plastic mulch strips after the soil has been prepared in spring, prior to planting. Mulches are often applied in conjunction with drip irrigation systems.
Purpose: Depending on the colour, thickness and nature of the mulch, you can achieve different results. Plastic mulch is most commonly used to stop or prevent weed growth, reducing competition for crops. Black mulch is most common, but most plastic mulches (other than clear) block light and stop weed growth. Coloured mulches can reflected certain wavelengths of light back into the canopy, with different results. Some mulches allow more soil warming than others. Most mulches reduce moisture loss, simply due to being a physical barrier to evaporation.
Cover/companion crops?
The planting of cover or companion crops might fit into the same category as the previously listed covers. If cover crops are planted in spring along with the focal crop, typically these serve the purpose of providing some degree of protection or sheltering influence on the crop. They may also provide some nutrients or some other beneficial amendment, usually once they are incorporated into the soil.
Conclusion
When it comes down to it, using a cover in conjunction with a crop can provide significant benefit. It means accelerated or improved growth, reduced competition or impact from external influences (weeds, pests, temperature, etc.), all resulting in potentially higher yields.