The quest to find the best soil

Just which compost to choose for our precious chillies?

Loam. Peat. Coir. Grit. Vermiculite. Sand. Clay. Silt. Perlite. Manure. Compost. Sand. So much to consider.

The options are a little overwhelming but let’s dig down to what we know about chilli plants to see if we can come up with our perfect potting medium.

Cultural roots

Considering the geographical heritage of our chilli plants should hopefully give some guidance to the type of soil required for perfect chilli production. Chillies originated from Mexico. They gradually became mainstream as part of the Columbian Exchange in the 15th & 16th Centuries. A large percentage of the soil in Mexico is shallow to medium depth, dry, free draining, not layered or super structured, contains gravel, often fertile, pH leaning towards acid: 5.5-6.5. (Food Agricultural Organisation for the United Nations state that Leptosol, Regosol and Calcisol make up nearly 65% of the soil in Mexico if you want the scientific terms) Replicating this soil composition seems like a good starting point for creating the perfect chilli compost.

Back here in the UK

However, where chillies come from is not the only factor in soil choice. Surely where they are actually going to grow plays a part too. The UK offers a dizzying range of soil types, some of which would be incredibly inhospitable to a poor little chilli plant. Our Hampshire soil is about 6 inches top soil and then solid chalk. Not sure what our chilli amigos would say to that. A slightly acid, sandy loam in the South Hams of Devon would be perfect for growing chillies in the ground. With that in mind, we will be planting in pots.

Our UK weather is such that too much organic matter, such as peat or manure, silt or clay could easily become water logged and get cold. No one likes a soggy cold bottom, especially not chilli plants.

The potting soil in question will have two main functions for our plants: 1. to provide a habitat for our chilli roots to do their thing. 2. To be a vessel for the chemical requirements for great plant growth and chilli production. Let’s tackle each function separately.

A cosy home

We want the roots to have plenty of space to stretch out. Soil is typically 50% solids (mineral and organic) and 50% spaces, about half of which is occupied by water and soluble and suspended nutrients. A light, airy soil, with small particles would match the requirements. The roots can work their way through the gaps.

We will be gradually moving our chillies into progressively bigger pots. They sulk for ages if the pot size goes up too quickly. The indicator that they need to move home is when their roots poke through the bottom. Watering from the bottom should avoid compaction (which leads to a reduction of spaces within the soil available for root growth & essential gas, water and nutrient storage). Perhaps a layer of Horticultural grit in the base of each pot would avoid aforementioned sulky soggy bottom too.

Adding Perlite to the mix is another way to allow the soil mix to stay loose, encourage root growth and water drainage. No rotten roots here.

Feed the need

No great nutrient supply is needed from the soil solids as we will be feeding with Chilli Focus regularly. The organic components of the soil provided by the garden compost will ensure a good supply of microorganisms to exist alongside our chilli plants and work their bio magic. No doubt a few extra seeds will germinate as well but that is all part of the fun of doing things yourself.

We do not want too much green Nitrogen releasing organic matter. We hope to encourage good all round plant health and then fabulous flowering and fruiting. Extra Nitrogen may cause bushy green plants that forget to flower.

The seedlings are currently receiving a weekly feed of 5ml per litre of Chilli Focus. This will increase to 10mls per litre once a week when the plants have been pinched out and show some signs of flowers forming. At the height of flowering and fruiting the plants will have two feeds each week.

Vermiculite is another ingredient to consider. A natural product that is a good addition to any soil type. Added to clay soils it allows aeration and flow through the soil, reducing water logging and stunted or bound root growth. In sandy soils it soaks up water allowing retention where there would be very little otherwise. Good access to water, slowly released, means good access to those soluble and suspended nutrients. Sounds like Vermiculite is definitely going into our chilli mix.

So what does this all mean?

It’s looking like a hand mixed potting medium of 3/10 loam top soil, 2/10 coir, 2/10 organic homegrown well rotted compost, 1/10 grit for the bottom of the pot, 1/10 vermiculite to hold on to water and nutrients between watering and feeds, 1/10 perlite for free drainage within the soil. Probably very similar to John Inness No 2!

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Feeding time at the zoo

It’s time to give these little chilli seedlings a bit of what they fancy. They have been potted on into seed compost and are settling in admirably. The seed leaves are opening, they are a good green colour and generally they look healthy. The seed compost has no nutrients in it though.

Seven day old seedlings looking healthy after moving into their newspaper pots.

In the future we’d like to have a go at producing a homemade, maybe organic, specialist chilli feed. Using local ingredients. Perhaps with a seaweed enrichment? But not just yet.

Seemingly THE recommended chilli food is Chilli Focus. Containing ‘A precise formulation for optimal performance of chillies and peppers in pots, grow bags or the open ground.’ We used it all last season and the chilli plants and crop were spectacular. It turns out that Chilli Focus is ‘Made with care in the UK’, and ‘enriched with organic complex plant acids and pure concentrated extracts of kelp’ and comes in a 5 litre bottle, ‘enough for 1,000 litres of feed’.

With added Kelp extract

Err, sounds pretty good to us. Homemade fertiliser can wait for further research on a rainy (or snowy, check the forecast!) day.

The seedlings have been given a gentle dilute feed of 5mls per litre. This will be given once a week for now. Once the plants start to flower it will increase to 10mls per litre and then twice weekly when they set fruit.

Pots Galore

It’s been a while. Busy times, you know. A quick status update shows that the February planted seeds are now in 9cm pots, they have 4-5 pairs of true leaves and are being fed ‘Chilli Focus’ plant food once a week (10mls to 1L). The March chitters are in their coir pots. Most have at least one pair of true leaves.

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So what happened in the chitting experiment? Jalapeno, Bulgarian Carrot, Aji Limon, Prairie Fire and Pretty Purple were all stars. Pretty much 100% success rate with the chitting within two weeks. Somewhat confusing results from the other candidates. Scotch Bonnet gave a 50% show. Fresno sent us three germinated offerings. Serrano & Long Slim Cayenne a couple each. Still NONE from Tobago Seasoning and Go Chu. None whatsoever. Disappointing to say the least.

The conditions were a little varied but surely one or two of each seed type should have germinated? We did take a holiday to Cornwall. The seeds were kept warm in the boxes at the back of an Aga the size & colour of a fire engine. They were also kept in the light. One Serrano showed his head in that week but then a few more of the harder types followed suit. Maybe light exposure is also a factor for some chilli types?

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There was also a brief foray into chemical assistance to germination. Some seed cases are tough and can be helped to soften using a couple of techniques: presoaking before chitting and using tea to soak them in. The tannins in the tea helps soften the seed case to allow more moisture in and then the root to break out. Not sure if I am committed enough to try diluted bird poo as a chemical aid. Might try scarification though.

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One tiny glimmer of hope remains in the fact that lots of books, seed packets and website claim that chilli seeds can take up to 5 weeks to germinate. All remaining seeds are basking in warm sunlight during the day and in the airing cupboard at night. If any of the Tobago Seasoning or Go Chu germinate they will be the most precious plants EVER. Definitely ones to overwinter. Come on now, play nice and give me couple of the plants I really want