Compost is a critical factor in the growth of plants because it helps to loosen the soil, more so compact soil that is clumped together in clods.
On the other hand, if soil is too loose, adding compost helps to clump it together to the desired level of compactness.
These two functions of compost lead to a balancing of soil density, allowing plants to develop optimally with much healthier roots, leading to healthier growth.
Definition and role of compost
Compost is decomposed organic matter that provides essential nutrients to plants when added to the soil. It is therefore a form of fertilizer.
Compost improves soil structure, helping it to hold sufficient amount of air, nutrients and moisture.
It also increases humus in the soil and introduces beneficial microbes that help to reduce soil-borne diseases and to suppress pathogens present in the soil.
How to know my compost is ready to apply
Compost is ready for application into your garden any time from 1 to 12 months, depending on factors such as level of garden management and quantities of materials used in making the compost.
Compost used for growing potted plants must always be allowed to compost thoroughly because if it is not allowed to mature, it will attract pests and causes damage to plants.
It will also use up the very nutrients meant to support the healthy growth of your plants. On the other hand, if compost is intended for use as mulch, you need only to wait for about 1 to 3 months before using it for this purpose.
Signs of mature compost
You will know your compost is ready to use when:
- The initial organic materials that you put together are no longer appearing the same way they did at the beginning.
- The compost has changed to a rich, dark-brown color, crumbles in your hands and smells like earth.
- The compost pile reduces to half of its original size/volume.
- The compost is no longer generating much heat like it initially did. However, this will be the case only when applying a heat composting method.
Compost that has not matured for its intended use needs to be given ample time for the curing process to be completed. The compost should always be aerated and kept moist during the curing process.
Can I put compost on top of soil?
Compost can be put on top of soil without mixing it with the soil if the sole purpose of use is to mulch your plants. However, if the intended purpose of use is to provide nutrients to plants, then this will not be helpful.
For compost to be beneficial in terms of providing nutrients to plants, you will need to mix it well with top soil. Apply 1 to 2 ½ inches of compost on the soil then till it 6 inches deep into the soil.
How long does compost last in soil?
The duration of compost in soil is largely dependent on the kind of plants grown and the space in which they are grown.
For instance, if you are growing a tree in a container or pot, you will need to replenish your compost every one to two years.
Within this time, nutrients present in compost will have been depleted and a new supply of nutrients from fresh compost will be required for optimal growth.
Rate of loss of nutrients
Generally, nutrients tend to be lost quickly in pots and containers. However, when it comes to growing other plants such as food crops, and horticultural plants such as flowers in a garden or farm, compost lasts throughout the growing season until the next growing season.
Old compost tends to be greatly depleted of nutrients, microbes and structure, making it of little benefit in a new growing season. Every growing season therefore requires fresh supply of compost.
Do I need mulch on top of compost?
Yes, you need mulch on top of compost because it helps to suppress the growth of weeds. It also reduces evaporation of soil moisture and adds organic matter into the soil upon decomposition.
However, it decomposes at a much slower rate than compost, making it necessary to always use compost for the purpose of providing nutrients to your plants.
How often do you need to reapply compost?
Compost should be reapplied yearly to replenish old compost in your garden. Old compost decays over time, making it useless to growing plants in terms of providing them with nutrients.
However, compost is not beneficial when used as mulch because it does not prevent the growth of weeds but instead promotes it by feeding them.
Frequency of application also depends on the frequency of use of the garden and the type of plants grown. For instance, if plants are grown in containers or pots, you will need to reapply compost every 6 months.
Should I spray my compost with water before applying?
It is not necessary to spray compost with water before applying it your garden so long as it is already sufficiently moist.
However, it is advisable to water your garden after applying compost because it helps the compost nutrients to seep down all the way through the top soil to the subsoil.
Ideally, compost should feel as wet as a damp sponge prior to application. However, if for whatever reason, your compost is not moist prior to application, place an oscillating sprinkler on your garden after spreading compost on it and let the sprinkler run for an hour. This will make your compost sufficiently moist.
Wet or dry compost – which is best to apply?
Wet compost is best to apply in a garden or farm because it helps to keep the living organisms within it alive.
These living organisms are the ones responsible for breaking down the organic matter in compost, therefore when compost is allowed to dry out completely, they die. Water it often to keep it moist.
Avoid making it soggy thou. Soggy compost interrupts the composting process, slowing it down and eventually stopping it. Again, too much water prevents air circulation within the compost, thus interfering with the activity of the compost microorganisms.
Lack of air circulation also makes compost slimy and full of bad odor which attracts flies.
Moisture content in compost
The amount of moisture in compost should be 40% to 60%. This helps the compost to generate enough heat for compost breakdown, making it light, frothy and fine for application.
It also encourages aerobic decomposition as air is able to circulate well deep within it. Dry compost can also be made and kept moist through constant addition of grass cuttings and food scraps without having to add any water directly.
Use a compost moisture meter to measure the moisture content of your compost. You will get one from an online market or from an agricultural store.
Causes of too wet compost
- Poor air circulation or total lack of it.
- Using too many greens. Whenever too much of green composting materials such as vegetable scraps are used, compost becomes overly wet.
- Using compost bins that lacks ventilation.
- Too much rain.
- Excessive watering.
- Poor or insufficient drainage.
Anaerobic compost also produces ammonia-like substances that gives off an unpleasant smell. It also produces methane, a greenhouse gas that harms plants by increasing surface ozone that causes yellowing of leaves.
What happens if you add too much compost?
Adding too much compost in soil leads to excessive accumulation of nutrients such as calcium, magnesium, potassium, ammonium and sodium, and also causes soil to develop high concentrations of carbonates and bicarbonates.
Nutrients such as phosphorus and potassium leach past the root zone of plants and even find their way into surface and ground water through irrigation or rainfall.
Surface water nutrients promote lack of sufficient oxygen in water and growth of algae. Excessive nitrogen causes compost to heat up too quickly, leading to combustion and risk of fire breakouts.
Too much compost also burns the roots of your plants and seedling stems whenever the concentration of nutrients within it is too high.
Does compost go bad over winter?
Winter has the effect of slowing down the decomposition of compost. Compost must therefore be stored properly during winter as repeated exposure to very cold temperatures affects the health of any compost.
Store it in such a way to allow the continual breakdown of all organic matter in your compost. If compost pile becomes frozen, decomposition will stop completely.
However, if you do your composting in large compost piles during winter, the organic matter in the interior of the pile will continue decomposing, albeit slowly because it will remain fairly warm, but the exterior compost will need help to continue composting.
Insulate your compost
Insulate your compost during winter by surrounding the sides of your composting bins with 6 to 12 inches of sawdust, leaves or wood chips to create a buffer against freezing temperatures. You can also surround your bins with bags of leaves or straw bales for insulation.