The Best Compost For Growing Fruit, Vegetables, And Herbs

Choosing compost can be confusing. This guide covers how to choose the best compost for growing fruit, vegetables, and herbs. It starts by defining what compost is, and why it is not the same as the soil, or earth, we have in our gardens, before looking at what makes a soil healthy, as compost is only part of the story in providing the ideal environment for plants to grow well.

From this understanding of what plants need to grow, it discusses the different types of compost available, the best compost for seedlings, what multi-purpose compost is, the type of compost found in grow bags, ericaceous compost, compost for more mature plants like fruit bushes and trees, and compost for house plants. It looks at what John Innes compost actually is, and what the numbers John Innes Number 1, John Innes Number 2, or John Innes Number 3 mean when they are printed on the outside of compost bags.

Watch the YouTube video below, or continue scrolling to read the full article on choosing compost.

Step By Step Video

YouTube Video

What Is Compost?

Compost is made from organic matter, like food waste, grass clippings, or shredded woody material from bushes or trees. There is a wide range of ingredients that can go into making compost, but in general terms, compost is made from roughly equal amounts of green materials, sometimes called wet materials, like food waste or green plant material, combined with dry materials like shredded wood.

Each manufacturer of compost will have their own recipe for making compost. But inside their compost, manufacturers often add additional material like fertilisers, or aggregate, to change the texture of their compost.

For plant growth, the crucial point is that compost is the result, or the end product, of a natural composting process, where bacteria, fungi, and organic organisms like worms, break down all the goodness in the raw materials, and convert these into nutrients that plants can use to help them grow. It is an almost magical recycling process. And depending what plant material is used at the beginning of the process, this will affect what nutrients will be available at the end.

The raw ingredients used partly explains why composts are different, combined with what manufacturers choose to add into their compost mixes afterwards.

How Is Compost Different To Soil?

Compost is only one part of garden soil, and in soil science this is often referred to as organic matter.

By contrast, soil contains other ingredients, and put simply, a large percentage of soil is made up of weathered rock, and by weathered rock, this means minerals. These minerals amount for a little under 50% of soil by volume. The size of these minerals greatly affects the texture of a soil, and how well water, or rain, moves through a soil. For example, a clay soil has small minerals that pack tightly together, and this type of soil is wet and heavy. Whereas a sandy soil has relatively large minerals, and this allows water to pass through it quickly, sometimes too quickly for plants, making the soil light and dry.

The minerals found in soil typically come from the original weathered rock beneath it, but sometimes they have arrived in an area from movement by glaciers, or volcanic action. Or in a garden, most likely builders could have brought in soil from somewhere else.

Therefore, the words compost and soil have their own specific meanings. Whereas compost is almost all organic matter, soil contains much less. And just as compost contains different nutrients based upon what the compost is made from, a soil will contain different minerals based on the original parent rock.

What Do Plants Need To Grow?

The differences between different types of compost, based on the ingredients used to make the compost, and soil, based on what parent rock was weathered to make the soil, explains why plants need different things to grow. This is because plants have adapted to the environment that they originally came from, and this adaptation means they perform better in some growing media compared to others.

What this means in practice is that there are two main considerations:

• Firstly, the ph value of a soil, which is often described as how acidic it is.
• And the second is how rich a soil is in terms of the nutrients it contains, to help plants grow.

pH Of Growing Media

Some plants have adapted to grow best in more acid soil. These include crops like potatoes, rhubarb, sorrel, blackberries, blueberries, and raspberries.

Other plants prefer a more alkaline soil, and these include cabbage, kale, cauliflower, and fruit like grapes and plums.

And then there are the plants that prefer a neutral soil like peas, onions and shallots, as well as spinach and chard.

Richness Of Growing Media

Some plants grow best in rich growing compost, or compost that contains a lot of nutrients. Tomatoes, courgettes, and winter squash are all greedy plants that will provide a bigger harvest when grown in rich growing media.

For other crops, the harvest size can actually be reduced if grown in too rich conditions. For example, peas may produce lots of leaves, but few pea pods, if grown in a rich compost.

The age of plants is also a factor. Seeds contain all the nutrients they need to grow, so at this stage of growth, having extra nutrients in a rich compost is not required.

By contrast, when planting perennial plants like fruit bushes and fruit trees, using a rich compost can both boost growth and help sustain the plant over the years ahead.

What Is A Healthy Soil For Plants?

So far this articles has introduced many of the differences plants have, and whilst this knowledge is important, it can make choosing a compost seem a little complicated.

Whilst having a basic understanding of what different plants need to grow is important, there are many things that plants have in common. So, whilst plants have their own nutrient and soil preferences, there are many common factors too.

The nutrient requirements for plants are similar. All plants need moisture to grow, as well as carbon and nitrogen. Water comes through rain, carbon from the air, but plants need to get their nitrogen from soil or compost. Whilst nitrogen is the most important nutrient, plants also need others in much smaller amounts, and these include phosphorus, potassium, calcium, zinc, magnesium, and copper to name a few.

The good news is that nearly all compost contains these nutrients. It is only the richness of the nutrients that tends to vary.

In addition, plants grow best in a healthy soil, and a healthy soil needs a good soil structure to allow water and air to move through it, and soil life like bacteria and earthworms to break down plant waste into nutrients plant roots can absorb. This is common across all plant types.

Therefore, because plants have common requirements for nutrients, and a good soil structure, this makes it possible for a general purpose compost to work for the large majority of plants.

Or said another way, whilst plants may perform best with a compost specific to their needs, they will still grow well with a general type of compost.

Can I Make My Own Compost?

As mentioned earlier, compost is nothing more than a combination of green or wet garden waste, like food waste or grass cuttings, mixed with brown or wet material like shredded branches. And when these ingredients are combined together, the composting process will start naturally.

There are three challenges when using homemade compost:

Moisture Content

Firstly, homemade compost is often too wet. This is because a gardener most likely has more green than brown materials. If using homemade compost as a mulch that goes on top of growing beds, this is not a problem. But if used as a growing media, it may be too wet, and not have enough air inside it for plants to grow well.

Seed Viability

Secondly, it is possible for seeds to survive a composting process, whether that is grass seed or garden weeds. Hot composting, which uses composting containers that trap heat, will kill these seeds. However, if using traditional cold composting in a compost heap, a gardener may find that when using their homemade compost, it spreads weeds around their garden, or results in weeds growing in their seed trays when trying to germinate seeds.

Time

Thirdly, traditional composting takes time, sometimes up to a year, or longer. This means that if a large quantity of compost is required, it will require a large amount of space to be dedicated to a compost heap. Sometimes, it is not practical to do this.

None of these reasons has stopped me making my own compost. But because of the reasons I’ve just described, I do buy shop bought compost too, especially for germinating seeds.

Compost, Peat, & Sustainability?

Peat has many properties that make it an excellent ingredient for compost. It is made from organic material that has not fully composted, and when added to a compost mix, it helps to create a good structure to allow water and air to circulate, as well as acting as a source of nutrients like nitrogen.

Unfortunately, peat forms in relatively rare waterlogged ground conditions, and it takes many years to even create a thin layer of peat. Peat is commonly extracted from existing peat bogs, rather than being mass produced, and therefore it is not a sustainable resource.

And for that reason, I choose to use peat free compost, even though peat is an excellent ingredient for growing plants. When buying compost, the packaging of compost often makes it clear whether a compost is made without peat.

The Different Types Of Compost

This section looks at the different types of compost it is possible to buy, starting with John Innes compost.

What Is John Innes Compost?

The name of John Innes on compost bags can be confusing, because John Innes is not actually a brand or manufacturer of compost.

Rather, John Innes takes its name from a wealthy benefactor who founded a horticultural research institution, and this institution in the 1930s created a recipe for different types of compost, based on scientific research of how the compost helped plants to grow.

The original recipe used a combination of soil, peat, and sand, but since then, peat free variations have been developed. A distinctive feature of John Innes is the use of soil in the body of the compost, instead of just compost. The use of soil adds more body, or weight, to the compost, with peat helping to provide a good soil structure and provide nutrients. The use of peat, as I mentioned before, is a challenge from a sustainability standpoint. But today, there is a selection of peat free John Innes variants.

At the time of creating this article, there is a manufacturers association that specifies the recipes for John Innes compost, and these recipes are followed by manufacturers when creating their brand of compost.

But not all John Innes labelled composts are identical, as although producers need to follow the recipe, the recipe allows for variation, for example in the use of peat and peat substitutes, and some flexibility in the percentage of different ingredients.

One of the distinctive features of John Innes compost is the simple naming of the different recipes, which are based on the life stage of the plants.

John Innes Seed Compost

John Innes Seed Compost is, as the name suggests, for germinating seeds. But it is also used as a planting media for plant cuttings.

John Innes Number 1

John Innes Number 1 is for young seedlings before they are transplanted to their final growing position. It is lower in nutrients than other types, to suit the growing stage of the plants.

John Innes Number 2

John Innes Number 2 is a general purpose mix for established plants. It can be used for growing vegetables in troughs and containers, and also for house plants. It contains double the amount of nutrients compared to John Innes Number 1.

John Innes Number 3

John Innes Number 3 is the most nutrient rich recipe. It is designed for larger plants, bushes, and shrubs. Given it’s high nutrient content, it is also good for greedy plants like tomatoes and squash.

There is also an ericaceous compost, but I’ll talk more about ericaceous compost later.

Speaking personally, what I like about the John Innes approach, is that it provides clear guidance on what each John Innes numbered compost is designed to be used for.

Other Composts

Aside from John Innes compost, there are many other composts to choose from, and as I mentioned at the beginning of the video, these include compost made entirely of organic matter, meaning without containing soil, or loam, which is a relatively rare resource. And as I said before, I choose compost that includes the words peat free on the packaging.

The absence of soil and peat in these composts can make these composts lighter compared to John Innes recipes. Instead of soil, these composts may include additional ingredients like sand and grit to help their texture. I’ll describe these composts in this part of the video.

Seed & Cutting Compost

Seed and cutting compost has a fine texture and relatively small particle size, to provide ideal growing conditions for sowing seed and potting up plant cuttings. The fine texture is created by processing, or milling the compost, to reduce the particle size.

The small particle size can create problems with drainage, and for this reason, the compost often has added grit, or sand, to create gaps in the compost to allow air and water to pass through.

General Purpose Compost

Compared to seed compost, general purpose or all purpose compost has a more coarse texture. It is often possible to see shredded wood within the compost mix.

I use general purpose compost frequently for sowing seeds and taking cuttings, and I’ve found it to work well.

There are general purpose composts with added nutrients, or other properties to boost plant growth. With so many to choose from, I cannot recommend one type over another.

My personal experience is to use a normal general purpose compost, unboosted with other ingredients, and then feed my plants when watering later in the growing season, if required.

Ericaceous Compost

There are some plants that prefer more acidic growing conditions, and for these plants, I buy ericaceous compost to help them grow well.

For example, when I planted my blueberry bushes on my allotment, I added a bag of ericaceous compost to each planting hole, and they have performed very well since then.

Grow Bags & Tomato Planters

There are many types of grow bags. Typically, these contain a general purpose compost, with added ingredients to help with moisture retention. Extra nutrients are sometimes added to boost growth.

Perhaps the biggest advantage of grow bags is their convenience, with the ability to grow plants directly in the bag, without the need for repotting.

Compost Ingredients & Specialist Compost

This section introduces common ingredients to add to shop bought compost, as well as a couple of specialist growing media.

It is common for gardeners to add ingredients to their compost to suit the particular growing requirements of plants. These ingredients often help with drainage to create a lighter, less wet soil, or alternatively, to help with water retention, whilst still allowing a good structure for air and water to pass through.

Grit

Grit is added to compost to help with drainage. Compost that consists only of organic matter, or with low soil content, has a tendency to shrink and stick together. Adding grit helps by creating air spaces in the soil, to keep the soil structure open.

I like to keep a bag of grit at home for exactly this purpose. I regularly use the grit when preparing compost for pots, for example to grow heat loving herbs like thyme, basil, and coriander. These herbs, and many others, prefer a free draining soil.

Perlite

Perlite feels a little like polystyrene, but is made by heating a type of rock until it expands and becomes filled with air. Like grit, perlite helps water to drain through a compost, but perlite itself also absorbs water, and therefore helps keep moisture in the soil.

Because perlite is so light, it can also be used to provide a thin covering over surface sown seed.

Vermiculite

Vermiculite is another natural mineral that is used in a similar way to perlite. It improves water drainage, and by absorbing water, helps to keep the soil moist. It’s light brown colour gives a compost a slightly more natural appearance that the bright white colour of perlite.

Mushroom Compost

Mushroom compost was developed as a by-product of the mushroom growing industry, and may contain peat if this was used for growing mushrooms. It contains many nutrients, and is commonly slightly alkaline in nature, which is helpful when growing crops like cabbage, kale, and broccoli.

Coco Bricks

Coco bricks, that contain coir, are made from the hairy husks of coconuts. They are sold dry, and then hydrated in a bucket of water before use. The coir is excellent at retaining water, and is often used as a substitute for peat in compost formulations. Like peat, coir has the ability to retain moisture, whilst improving the overall texture of a compost, allowing water and air to pass through.

My experience with coir is that whilst it is excellent at retaining moisture, it does come with one disadvantage compared to peat. Unlike peat, coir does not contain nutrients. Therefore, I need to add additional nutrients when watering to make up for this to keep the plants growing well.

Orchid Potting Mix

And to complete my look at compost ingredients, is to show a specialist orchid compost potting mix. Orchids are a great example of specialisation, as they grow on a bark based compost with very little, if any, green organic matter.

Understanding where orchids come from, helps with selecting the best compost to use. Orchids grow in tropical rainforests, and are often found in trees at the point where a branch meets the main trunk. Therefore a bark based compost matches most closely to the growing conditions the plants are adapted to.

How I Choose My Compost

Before finishing the article, I want to share what compost I buy and how I use it.

At home and on the allotment, I always want to have available:

• General purpose compost
• Gardening grit
• And a supply of homemade compost

At the beginning of the growing season, I may purchase a bag or two of seed and cutting compost for germination, but only if I have run out of general purpose compost at the end of the last growing season.

Seed compost generally comes in smaller bags than general purpose compost, and as it is designed specifically to germinate seeds, I sometimes buy it out of convenience.

But most often, I will use general purpose compost for all my growing needs. Depending on the plant, when potting up, I will add grit to the compost to help with drainage. However, I’ll only add grit if the plant really needs it. I mentioned earlier I use grit for mediterranean herbs, but I’ll also use it for pot plants like aloe vera and other succulents.

If I am planting out greedy vegetables like winter squash or courgettes, or fruit bushes, canes, or trees, I will mix either my homemade compost, or general purpose compost, with garden soil in the planting hole. Adding compost helps to feed the plants, whilst the original soil gives more weight and stability.

I use my homemade compost to feed and condition my existing garden and allotment beds, as well as plants that have permanent homes in large containers. My homemade compost is quite wet, but it is excellent as a mulch that goes on top of the soil. Life in the soil will quickly draw it down below the surface, and the sun will help dry it out.

And, when required, I may make a special trip to a garden centre to buy ericaceous compost, but only if I need this to add to a planting hole of an acid loving plant, like a rose bush, hydrangea, or blueberry bush. If I’m simply feeding the plants, I’ll use my homemade compost as a mulch.

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