Composting is a foundational practice in nature-friendly farming, crucial for growers of all types and scales. Yet, it can often feel overwhelming with its array of techniques, ingredients, and maintenance needs. We caught up with Emma Restorick, a grower at Prideaux Walled Garden and trialist in the Farm Net Zero field lab that’s optimising compost management. One of her main focuses in the trial has been controlling bindweed, a persistent challenge for horticulturists in perennial borders and no-dig systems. 

In this article, Emma shares her expert insights on improving compost quality through effective moisture management, the use of microbial supplements, and the importance of regular turning.

How to control bindweed - use compost

Bindweed is thought to thrive in compacted soils with low organic matter. Emma’s trial investigated whether compost application could be a solution, testing on two types of soil strips: one aerated with a broad fork and one not. The objective was to determine if soil aeration, combined with compost, could be an effective method of bindweed control whilst improving overall soil health. She also investigated whether adding different microbial supplements impacted the presence of bindweed.

The first year of results indicate that improving the soil biological diversity with compost, and reducing compaction with broad forking, can be highly effective at suppressing bindweed below and above ground. Additionally, a mix of anthelmintic cover crops and land sheeting appear to have further reduced bindweed growth. While the microbial supplements had no visual impact on bindweed vigour, Emma found that adding high-quality compost and improving aeration significantly reduced bindweed infestation in just four months.

Reflecting on the results, Emma shared: “It was just amazing. I realised how much more compost I need to make because a really good application of homemade, microbially rich compost significantly reduced the presence of bindweed. Increasing organic matter and aerating the soil allows it to function better and make full use of that organic matter.”

Emma is planning a second year of trials with more replications so that firm conclusions can be made on the use of the broad fork and compost at tackling bindweed.

Why moisture is crucial for composting

One of the most important factors in creating top quality compost is maintaining the right moisture level. "The bacteria really need water to thrive," Emma explains. "Once it’s dried out, everything just grinds to a halt." To ensure optimal moisture, Emma waters her compost every time she turns the heap. She advises that the ideal moisture content can be tested by squeezing the compost: "If you get one drop of water, that’s what you’re ideally looking for in finished compost."

Composts with a lot of dry materials, such as wood chips, generally need more water. In contrast, composts rich in nitrogen (such as manures, food scraps and green leaves) may require less watering.  As a rough guide, the ideal carbon-to-nitrogen ratio is about 25 - 30 parts carbon for every 1-part nitrogen, but Emma’s hands-on approach helps her maintain the right balance: "It’s just one of those things you get a feel for the more you work with it."

How to turn your compost for the best results

Turning the compost heap is essential for maintaining aerobic conditions. Emma has found that frequent turning helps regulate the temperature and ensures even decomposition. "I turned the compost on Monday, and by Wednesday, it got up to 70°C, which is a bit too hot. So I turned it again to bring the temperature down to around 60°C, which is ideal for killing weed seeds without harming beneficial bacteria."

Emma suggests that the frequency of turning depends on the heap's temperature and smell. "When it gets too hot, or if it smells sulphuric which is an indication that it’s starting to go anaerobic, it’s time to turn it. By managing the heap regularly, you get better compost, though it’s sometimes hard to find the time during the busy summer months!"

The benefits of adding microbial supplements to your compost

Emma has experimented with various microbial supplements to enhance her compost. She’s particularly interested in introducing bokashi to her main compost heap. "Bokashi seems to speed up decomposition, and worms absolutely love it. I’ve been using it on tougher materials, like ivy, before I add them into the main pile. The idea is to create a good balance between nitrogen and carbon-rich inputs."

In addition to bokashi, Emma has experimented with other microbial brews, including a Korean recipe of fish amino acids, and calcium-rich solutions made from eggshells soaked in apple cider vinegar. In the trials, the brews made little difference to the presence of bindweed, but Emma is interested in how they improve soil health. She noted that an application of the eggshell brew increased numbers of worms in the soil. In future, Emma wants to explore using microbial supplements to create compost tailored to the specific needs of different soils.

What ingredients do you add to your compost?

Emma believes in composting a wide variety of materials to create a diverse, nutrient-rich compost. "I compost almost anything. I hate the idea of sending stuff to landfill when it could be valuable in the garden. My compost includes a lot of wood chips, leaves, and coffee grounds, which are rich in nitrogen. I also use leaf mould, which creates a lovely, loamy texture."

Emma is also exploring the use of biochar, particularly from meat bones. "Biochar is porous and can increase soil carbon and water-holding capacity. It acts like a little hotel for beneficial microorganisms."

Dealing with weed seeds and diseased material

For many growers, composting weed seeds and diseased material is a concern. Emma, however, isn’t afraid to compost small amounts of problematic plants like bindweed. She advises turning the heap regularly to ensure weed seeds are exposed to the high temperatures in the centre of the pile.

Costs of bokashi and future plans

While there are costs involved in purchasing microbial supplements like bokashi (around £7 for 1kg), Emma finds them manageable at Prideaux Walled Gardens, which is an acre in total.

Looking ahead, Emma plans to expand her composting efforts across her entire garden. She’s also considering the use of cover crops, fungal inputs, and tailored compost mixes for different areas.
"I want to replicate my composting success across the whole garden. I’ll also start using bokashi more widely in my composting process to ensure it is as microbially rich and diverse as possible."

Emma’s top tips for improving compost

Emma encourages growers to experiment with their composting practices. "Don’t be scared to try different things. As long as you trust your senses and know what good compost should smell and feel like - a rich, dark chocolate brown with a lovely structure full of worms and no off smells - you can play around with different inputs and methods. The best compost often comes from a bit of trial and error."

She also recommended listening to podcasts on the topic. Two she’s found useful are the Composter Podcast, and The Flower Podcast with Jenny Love, which although isn’t focused specifically on composting is where Emma got a lot of her recent inspiration for microbial brews.

Interested in learning more about cutting-edge composting techniques? 

The Farm Net Zero composting field lab is where Emma and four other growers in Cornwall are trialling new approaches to compost turning, microbial supplements, and managing weed seeds and pathogens. Check out the field lab page to explore the latest updates and findings from this farmer-led research.