HOTBIN COMPOSTING IN AUTUMN
Autumn is Coming –
Here are a few tips for managing your HOTBIN after your garden clear up!
Time for the big autumn tidy up which means lots of waste. Unlike a traditional heap the HOTBIN will not freeze and continues to work over the winter providing you with a nice batch of spring compost.
To get HOTBIN composting in autumn here are a few tips to help you manage the tidy up.
Tip One: Shred waste where possible. A pile of hedge trimmings that fill a barrow will be a few cm high when well shredded. If you do not have a shredder, careful use of your hedge trimmer or lawn mower can suffice:
- Hedge Trimmer – pile up the waste on soft grass, cross cut repeatedly.
- Lawn Mower – pile waste on the lawn and run over it repeatedly with the mower.
We do not recommend either technique if the twigs are more than 5 mm thick.
Tip Two: If you have lots of brown fallen leaves and the grass is not too damp for one last cut, it is worth spreading the leaves on the lawn and cutting and shredding both in one go. The grass/leaf mix will compost super-fast in the HOTBIN.
Tip Three: Where you have too much, ensure your stock pile is protected from the rain. A large bag of wet cold leaves will be significantly harder to get hot than a dry cold bag of leaves. You will be amazed how quickly a mound of waste can be composted if you maintain 60C using the “little and often” technique.
Tip Four: Do not be tempted to add or squash everything in. Fast composting requires heat and heat requires airflow. If you compress it too much airflow will be restricted. Adding bulking agent (particialy composted woodchip) helps maintain airflow throughout the waste. If you add a lot of cold waste it will take longer to reheat. You are better off adding a 20-30cm (one foot) layer every 2 days over one 50 cm layer in one go.
Tip Five: If your HOTBIN is already full, then check your base layer to see if it is worth removing now. Even if the base does not look like perfect compost, it might be better to remove and use it as winter mulch or for digging in. This is not always easy to assess – if you need help view how does HOTBIN compost look and feel.
Keeping the HOTBIN Compost Bin Hot in Winter
The HOTBIN is capable of working at 40-60C all through winter.
Even when the outside temperatures of falls to -15C.
To achieve this, you will need to:
- Add waste regularly – at least once a week
- Add at least 5Kg/week (2 small, or 1 large caddy)
- Ensure you add lots of shredded paper (or corrugated cardboard) in with your food waste
- Re-start your HOTBIN if your waste drops below 20C (ie use the ‘kick start’ hot water bottle)
Not all customers will achieve hot composting over winter as they do not have enough waste. It’s good if you do but don’t worry if you don’t as you will be able to kick start hot composting when you start to get enough waste.
To understand why, you need an appreciation of the laws of nature that govern how the HOTBIN and bacteria work:
- Hot things cool down – the insulated walls slow the rate of heat loss, they do not stop it
- To keep hot, you need more energy going IN (food to generate heat) than the heat (energy) coming OUT, i.e. lost due to cooling
- Bacteria work faster, and hence generate more heat, at higher temperatures. They work very slow and almost not at all below 5C. Cold waste with cold bacteria are unable to generate enough heat to ‘warm up’ a cold bin in winter – they need a little help via a ‘hot water’ bottle to give them warmth to which allows them to get active and generate their own heat.
- A HOTBIN in an exposed windy site (e.g. middle of garden) will cool faster than one in a sheltered position (e.g. behind a wall). A windy location requires more waste.
What happens when it snows?
If the HOTBIN is running at 40-60C it will carry on working when it snows. Snow that falls on the valve is melted by the hot air leaving the valve. There are limits – so watch out for exceptionally heavy snow (like 5cm) as you may need to brush this off to keep the valve clear.
If your HOTBIN is luke warm (20-30C) then there will not be enough hot air rising out to melt the snow – you will need to wipe snow off the valve.
See the attached photo – we have two HOTBINs permanently on test at HQ. At this point in time one is running hot and the other has cooled down. Last night it snowed about 2cm.
How to start your HOTBIN in winter
Plus how to keep the HOTBIN hot in winter
From scientific angle, it is not that much harder to start the HOTBIN in winter than it is in summer.
From a practical standpoint it is harder because;
1) there is less garden waste around to create the minimum 40 cm base layer
2) In winter there is less ‘easy to consume’ waste (e.g. grass) and more ‘slow to consume’ waste (e.g. brown leaves)
How do new customers get going in Winter?
There are two options – which route you take depends on what waste you have available and to some extent on your willingness to actively seek out waste to ensure you have the right components. In the end not everyone wants this challenge. We have also noted a more laid back ‘patient’ approach.
Just be aware – we cannot change the laws of physics on heating and rates of cooling. If you do not have the quantity and type of mix to create heat, be patient you are going to have to wait until late spring.
The rule of thumb to getting started and getting the HOTBIN hot is: the more you add the easier it is, the more digestible the waste the faster heat is produced. If the temperature is below 10C (which it is most nights and days after September) you need to also ‘kick start’ the base layer in the HOTBIN with the winter heater (aka a hot water bottle!).
Fast – for those willing and able to search out enough waste
To get going you need a base layer – add lots of waste – at least 40cm (above hatch paneldoor) and more if available. Also ensure the mix has lots of easy to digest waste. As you are unlikely to have cut grass in winter – cheat as follows:
- Shredded office paper (or chopped up corrugated card) is easy for bacteria to digest. You need lots – think a 1-2 carrier bags full to start and several handfuls each week
- Add a handful of chicken pellet (poo) or blood bone meal from the garden centre each week. Buy big cheap buckets – and don’t worry – you are merely delaying the application of the fertiliser – all the nutrients will still be in your compost
- Add a few handsful of autumn leaves on alternative days – but not masses of cold leaves in one go. Leave time for the leaves to heat before adding more cold leaves. Drain rain water off from exceptionally wet leaves
- Add your kitchen peelings and food waste – but do ensure you also add shredded paper (or cardboard) and bulking agent too
Still not enough waste? Get creative…
- Seek out friends with allotments, larger families with waste, even your local grocer – and ask for waste
- Not enough shredded paper? Most offices produce sacks full of shredded office paper every day. Your company pays to dispose of this – ask for a sack full!
Once going you need to keep the heat up. This will require at least 5-10L of waste a week. It is even more essential in winter that your waste is not ‘too wet’. Always amend your mix with 30g (one large handful) of shredded office paper per one Kg of food waste. That is 2 handfuls of shredded paper per caddy. The easy way to do this is add the paper into the base of the caddy after each empty.
ALWAYS add bulking agent with food waste.
Using the ‘Kick Start’ bottle
Some people find this ‘amazing’ and they find they have a hot heap in 6-12 hours, others try it a few times, nothing seems to happen and give up. So here’s a little bit of background on how it works, and the essential thing to get it to work
The science behind the ‘heater’ is:
- Compost heat is a by product of bacterial activity (i.e. growth)
- More bacterial activity = more heat
- Bacteria do not grow much (or produce heat) below 5C and almost not at all at 0C
- When the waste is cold, only a tiny amount of heat is created by the bacteria and this is quickly lost. (Hence outdoor heaps stay cold/frozen in winter). The HOTBIN’s Insulated walls help retain heat, but there is still not enough heat to raise the temperature of the waste.
- Why add boiling water? 1 litre of boiling water contains 4200 J energy. The heat moves from the water into the cold waste and is retained within by the insulated walls for a few hours – the HOTBIN acts like a Thermos Flask!
- The waste heats up around bottle to 30-40C for an hour or so
- During this short period, bacterial activity increase 8-16 fold. More activity = more heat and the waste moves into a self sustaining increase in temperature
- There is enough heat to increase the waste temp – i.e. the HOTBON increases, rapidly towards 60C
The technique only works if there is enough easy to digest food waste.
I liken it to a human diet – if you eat a high fibre breakfast you get steady energy all day, but drink coke and sweets and you’ll be on sugar high for a hour! Since the heat from the bottle only last an hour or so, the bacteria need fast food during this hour.
If your bin is full of woody stuff that they find hard to digest, then no new heat is generated. The bottle works when bacteria have a diet of ‘fast food’ i.e. shredded white paper, food waste, cardboard, soft plant material (grass nettles, comfrey).
All the above might be a little too energetic for some users. Below is an alternative winter method.
Just be aware – we cannot change the laws of physics on heating and rates of cooling. If you do have the quantity and type of mix to create heat, be patient you are going to have to accept ‘warm’ rather than hot composting wait until late spring.
Patient winter method – for those unable to track down enough waste
Add waste ‘as it comes’ and let it build up over time. It won’t ‘take-off’ and get into the hot 40-60C range, more likely to move along at 10-30C. But this is still much better than a frozen open heap that is inactive. As with the fast method, the key in winter is to ensure your waste is not too wet – so add lots of shredded office paper and bulking agent.
Please note the Kick Starter Heater comes with the HOTBIN with all the extras. It is a 2-litre HDPE screw top container that can hold boiling water which you can pop into the top layer of the HOTBIN when it needs a winter boost.
Can I add Autumn LEAVES to compost in my HOTBIN
Leaves can go in the HOTBIN and they make great humus.
If you have a lot of leaves (>10 litres, a bucket load), you need to tweak the recipe to ensure they HOT compost.
If you only add thick layers of leaves into the HOTBIN, it is unlikely they will rise above 20-30C as the woody nature means they are hard for bacteria to digest and hence heat is released slowly.
To HOT compost autumn leaves, see the recipe below:
How to HOT Compost Autumn Leaves
There are two parts to successful composting of autumn leaves.
1) Adding a nitrogen source to balance the high carbon in leaves
2) Ensuring that there is enough ‘easy to digest’ waste (e.g. greens, food waste, shredded office paper’ (which creates heat quickly) to keep things hot whilst the hard to digest woody material (in which heat is released slowly) are also digested. In some cases solving (1) & usually solves (2).
Here’s what you need to do to ensure you get the best out of your HOTBIN
Step 1: Shred leaves
Leaves tend to form a dense matted layer that restricts air and oxygen flow within the HOTBIN. We advise shredding the leaves (e.g. using mower or a hedge trimmer).
Step 2: Mix leaves with easier to digest materials like food waste
Many people simply will not have enough food waste to mix with high volume autumn leaf fall. You can cheat a little by adding another easy to digest waste to go with the leaves such as chicken poo, chicken pellets, or a sprinkling of blood bone meal.
The ideal waste to mix with autumn leaves is grass lawn mowing – unfortunately, it is rare in UK to be able to get the mower out in Autumn as it is too wet and compacts the lawn soil. If you have room storing leaves in a wire frame box ready for spring and first grass cut can work really well . (Avoid sealing in black bags – the leaves will go anaerobic (see below for anaerobic method).
Step 3 – Do not add too many each time – little and often is best
More than 10cm (20 litres) of cold wet leaves in one go will “stall” the HOTBIN. The cold leaves will lower the temperature of the HOTBIN below 20°C and the heat production falls below that needed to re-heat. So store the leaves in a pop up bag, protected from rain and add over a couple of weeks – you’ll be amazed how fast they compost.
If you have a large garden with lots of trees and mounds of leaves then possibly doing a little bit each week in the HOTBIN is impractical. Try the following – shred the leaves (e.g. using lawn mower), store in a wire frame or cold compost heap until spring. Mix with first grass cuttings in large volume piles. Turn occasionally.
Leaf Mould Versus Composting
If you are collecting leaves into a wire frame then you might go down the route of just leaving them in the box and waiting 1-2 years for leaf mould.
Leaf mould versus ‘bagging’ i.e. anaerobic digestion
Many compost sites note that ‘bagging’ leaves in black plastic and tying off will create a black slime that can be used as compost. What this really means is you are anaerobically digesting the leaves down to compost. To an extent this is ok, our point would be AD creates methane and you are releasing a GHG that is 24 times more harmful than CO2. And we hope you would agree that every little bit avoided helps.
Aerobic composing is carbon neutral. Also to be honest – the black bags absolutely stink when you open then!
You can now successfully compost large amounts of Autumn leaves in your HOTBIN.