IMPROVING SOIL FERTILITY

There is a saying ‘healthy soil = healthy plants’, so it is no surprise that garden centres and nurseries offer a wide range of products to improve soils. Why do we need to focus on soil? How can one improve life in the soil and how often is it necessary to fertilise or add compost? 

First it helps to have a basic understanding of soil biology. Soil is not just dirt: there is a whole world under our feet, teeming with life which is invisible to the naked eye. There are micro-organisms such as bacteria, fungi, protozoa and algae which all play a role in making nutrients available to plants. Plants live in a mutually beneficial relationship with these micro-organisms: the plant roots give off substances which the soil microbes absorb and convert into nutrients, vitamins, growth regulators and antibiotics, which are taken up by the plants. So healthy soil is actually an underground grocery store and pharmacy for plants and trees.

Nearly all plants rely on fungi in the soil called mycorrhizae for nutrients and moisture. The fungi produce fine threads which increase the plants root surface area by 300 to 1000%. It is astounding to think that a tree may have a delicate network of fungal filaments that covers the size of a tennis court! Therefore it’s not surprising that digging or turning the soil causes major setbacks to plants and disrupts the ecosystem of the soil. So the best thing a gardener can do is spread a generous amount of organic matter on the soil surface and then do nothing. Earthworms will feed on the organic material and convert it to humus, and the soil micro-organisms will do the rest.  By feeding the soil, you are effectively feeding the plants.

How to improve soil?

There are multiple ways, and they usually involve the introduction of organic matter in one form or another. In newly made plant beds one can dig in compost, or adopt the ‘lasagne-style’ method of preparation, where one layers organic matter such as corrugated carboard, newspaper, kitchen waste, manure and straw or leaves. Another method used in permaculture is to bury logs and branches (hugelkultur) which slowly decompose and provide humus and moisture to plants growing above.

Sowing green manures is a time-honoured way of improving soil fertility. Fast-growing plants such as legumes, oats and/or mustard are sown to cover bare soil, smother weeds and prevent soil erosion. When dug into the ground while still green, they return valuable nutrients to the soil and improve soil structure. Legumes are particularly valuable as they have nodules on their roots with specialised bacteria that convert nitrogen from the air into nitrogen compounds – i.e. fertiliser for free! Using green manures is widely used in organic vegetable gardening and would be a cost effective method of soil preparation for larger landscapes and developments.

In established plantings, it is preferable not to disturb the soil and simply to mulch with organic matter – i.e. spread a layer of chipped garden material, straw or leaves. For most gardens and landscapes this is sufficient to meet the needs of plants.

How often to compost or fertilise the soil?

Here you need to consider the type of plant and its requirements. Vegetables require ongoing and regular inputs of organic matter and fertiliser. Remember that every time you pick a tomato, cauliflower or pepper you are in effect removing a concentration of macronutrients (carbon, nitrogen, phosphrous, potassium) and micronutrients (e.g trace elements) so these need to be replenished. Soil drenches and foliar feeding with ‘teas’ made of compost, manure, comfrey, seaweed and earthworm castings are all highly beneficial. Organic fertilisers made of plant, animal and mineral material provide a concentration of nutrients that become available to plants in a slow and sustained way, so there is no leaching or waste.

Plants growing in forests have an ongoing supply of leaves, twigs and branches landing on the forest floor which decompose and become compost. So forest trees, shrubs (e.g. plectranthus) and bulbs all enjoy regular dressings of compost.  On the other hand Strandveld species grow in the sandiest of soils, and fynbos is adapted to nutrient poor soil that is low in organic matter, so these plants require minimal or no composting when planted in ‘clean’ soil. Plant growth will be slower but more sustained without compost, which requires less pruning and results in a longer lifespan. However, cement and plaster from building activity changes the pH and requires generous amounts of compost to undo the effects of contamination.

Fertilising in a nutshell: Feed the microorganisms in the soil, and you will be feeding your plants.

  • Save ALL your organic matter (leaves, branches, trimmings) and recycle it on site – by chipping and composting or spreading as a mulch. No more exporting bags of green waste!
  • Kitchen waste and cardboard can be composted or processed in a worm bin or in a compost heap
  • Always mulch with an organic mulch (e.g. leaves, straw, chippings) as it will decompose and feed the soil
  • Use leaf blowers ONLY on paved areas. Ensure it doesn’t blow away mulch from plant beds as this will lead to soil encrustation and depletion
  • Feed and improve the soil according to plants’ specific needs – e.g. veggies need a lot and some plants don’t need much

 

Text and pics by Marijke Honig

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Bridging Waters event

“Bridging waters”  was the first of a series of events to be held at UCT’s Future Water Research Institute, a transdisciplinary initiative that enables researchers to work collaboratively in water science, engineering and society, in order to think differently about water capture, use, handling, treatment and management. Water Sensitive Design is one of Future Water’s flagship projects. Continue reading “Bridging Waters event”

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RESILIENT LANDSCAPING

Here is the 3rd communication from the Cape Resilient Landscaping Forum by Marijke Honig. This one outlines the importance of resilient landscaping and offers some tips and suggestions for creating and maintaining water-wise, resilient gardens and landscapes.

1. How has climate change affected weather patterns in SA?

The weather patterns are more unpredictable and extreme, for example there are prolonged dry seasons, then flooding.  We also experience wild swings from day to day – in Cape Town we had hot humid conditions and lightning in October followed by weeks of unusually cool weather, followed by a 40 C heat wave. And snow in mid November! The winters are becoming milder, which is an issue because fruit trees need a period of dormancy (rest) in order to produce well.

2. How can we respond to changing weather patterns in the way we manage our gardens?

We can respond by creating resilient landscapes and gardens that can adapt to changing weather patterns and bounce back after extreme events.

The drought has been a real eye opener in this regard: many people realised they had been overwatering their gardens, and that most established plants could survive and bounce back after the first rain.

Plants that require a lot of regular watering and feeding are obviously not suited to your garden conditions. Choose hardy resilient plants instead that thrive with least human input in your garden. Please note that resilient doesn’t mean only succulents! There are hundreds of resilient shrubs and groundcovers that can survive with local rainfall. Instead of working against nature allow natural ecological processes to take place. For example open areas will be colonised by pioneer species; fallen leaves and branches will decay on the ground, thereby mulching the soil and releasing nutrients through the natural process of decomposition.

3. How do we build resilient landscapes? 

  • Create structure in the design: ‘good bones’ using hardscape elements and hardy long-lived evergreens.
  • Create flexibility in the design and relax control: allow plants to migrate and ‘find’ their own place in the landscape – these will be the areas (habitats) most suited to them.
  • Challenge plants to survive on natural rainfall
  • Maximise the infiltration of rainfall to recharge the soil and create an underground moisture reserve
  • Create a closed system for your garden with no outputs (garden refuse) or inputs (fertiliser, compost, water, plants) – allow natural cycles to take place instead.
  • Select plants not on aesthetics or emotional attachment – opt for plants that can survive drought, tolerate a wide range of conditions and rapid recovery after a major disturbance. When resilience is the main criterion, weedy and self-seeded plants are not a problem but an asset: they contribute to the long-term sustainability of the landscape.
  • An adaptive response to changing weather patterns requires changes in the way we see and what we do. Perhaps the biggest challenge is that we have to undo old habits (overfeeding, overwatering) and do less. No more digging (which upsets soil microorganisms and disturbs roots), no feeding, no raking of leaves, no spraying for pests – it requires a much lighter touch and an attunement to natural processes. One can learn a lot by observing plant communities growing on un-irrigated road verges and natural areas – these are usually resilient and self-sustaining.

4. Some practical tips to create resilience.

  • Set yourself the challenge: zero storm water runoff from your property. Capture and store rainwater from roofs and air conditioners and ensure that all water runoff from paved areas goes directly into the soil. Avoid hard surfaces and choose permeable options instead (e.g. planted and mulched areas).  If you need a hard durable surface consider materials such as stone chip or peach pips – these can be stabilised with a plastic honeycomb like product called Gravelfix, or permeable paving.
  • Consider your garden like a giant underground reservoir or sponge, and do whatever you can to maximise the infiltration of water. Find out about rainwater harvesting and how to ‘plant the rain’. For more detail visit Brad Lancaster’s website https://www.harvestingrainwater.com. Ensure you have carefully planned overflow systems to handle downpours and prevent flooding.
  • Zone your garden into water-use zones, with a small high water-use area close to the house (e.g. pots or plantings seen from living area) and a large area allocated to a low or no water-use zone, using plants that can survive on natural rainfall.
  • Select plants for resilience: their ability to tolerate a wide range of conditions and bounce back after an extreme event
  • Use trees and large shrubs for creating shade, screening and privacy. Instead of building boundary walls, plant mixed hedges of indigenous plants – you will enjoy masses of greenery, foliage textures and flowers and create wonderful habitat for birds, bees and other wildlife.
  • Measure, monitor and manage your water-use carefully. If you have a borehole, it is now a legal requirement to install a water meterso that you can monitor water usage and detect leaks when they arise. Smart meters offer the convenience of real-time data on a handheld device in your home.
  • When watering water deeply and infrequently. Mimic a good rainfall event of say 50mm and really saturate an area, with water penetrating at least 50-60cm into the soil. Then you may only need to do this every 3 to 4 weeks.
  1. How can resilient landscaping save you money? 
  • By ‘planting the rain’ instead of letting it run off your property, and choosing appropriate plants, you can enjoy a lush garden teaming with life with minimal input. It really is the smart choice!
  • Strategically planted trees offer shade and coolness – saving you the capital investment and running cost of air-conditioning.
  • Wicking beds are a water-efficient way to grow veggies and provide ongoing access to fresh salad leaves, spinach, herbs and tomatoes, to name just a few of the easiest ones to grow.

Resilient gardens and landscapes make a valuable contribution to the urban ecosystem, making our cities livable, sustainable and a pleasure to be in.

Left: In the front, a resilient plant combination of red Kangaroo Paw (Anizoganthos), Cotyledon orbiculataEragrostis curvula and coral Hesperaloe parviflora in front, with the lacey grey foliage of Rhagoda histata (Saltbush) and Strelitzia reginae behind.

Right: Self-seeded plants like Geranium incanum are an asset in resilient landscapes, filling in any gaps.

Landscape Water Audit & Budget

Marijke Honig made this one page summary for a landscaper’s ‘water audit’. The idea is to work out a kind of water budget for the property, and design accordingly.
This could of course become a much more detailed checklist or planning tool.
Any comments/ feedback?

A Water Management Tool

Green Cape has put together this useful planning tool for water management and saving.

Many people in the industry have emphasized the need to do steps 1, 2 and 3 BEFORE considering alternate water.

Unfortunately the water crisis has meant that many people/ businesses have skipped straight to step 4: installing a borehole, without doing the metering and monitoring, and water saving technologies and behaviours first.
We can help raise awareness and educate clients in this 4 step planning process. Please share the tool widely!

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