CHOOSING A GROWING MEDIUM FOR YOUR GREENHOUSE
by Adrian White
20 December, 2021 by
CHOOSING A GROWING MEDIUM FOR YOUR GREENHOUSE
Lucija Johum

If you thought that there was only one way to grow in a greenhouse – think again.

Before you consider greenhouse growing and its many benefits, you’ll want to make sure that you’re starting out your operation right and making a smooth transition from your earlier growing method. Part of this involves selecting the plants that would be perfect for greenhouse growing, as well as the ideal location, materials, and plan of attack on managing one of these genius, efficient growing systems effectively.

Another important consideration is what you’ll grow your plants in, and how you’ll grow them. There are many different types of growing mediums (or “media”) to choose from, and each one may function differently when you put it in the scheme of a greenhouse. Further, the type of crop you choose to grow will also benefit from certain media over others – so choose wisely.

SOIL BEDS

If you’ve got good soils straightaway under your covers, why not utilize them? This is more likely in very agriculturally-rich areas, such as the Midwest, the South, or parts of the Northeastern U.S. In these areas, all you’ll need to do is some soil prep or amending with a nutrient-rich compost to get beds ready for your preferred greenhouse planting method.

If you have access (or want to have access) to mechanical equipment – from small tillers to large tractors – then direct planting in a soil bed may be just the thing for you. This is an especially popular choice for high-volume, wholesale vegetable farming or similar operation. For a tractor, however, make sure that your greenhouse would be large enough to receive it!

ROW CROPPING

Row cropping is one of the most common and traditional methods for planting one’s fare straight into the ground. It also pairs with mechanical methods the best: discs, cultivators, and other implements on a tractor are built to operate close to and around plant rows, making quicker work of a higher volume of plants.

If your greenhouse can hold a tractor and you are also considering large scale annual vegetable production, consider row cropping. Again, this is a common option mostly for vegetable crops, but also others like cotton, tobacco, and more – though these are less ideal greenhouse crops.

BIOINTENSIVE

If you are not interested in mechanized agriculture and are growing more on a smaller scale, consider a hand-labor, space-intensive method such as John Jeavons’s biointensive technique from his famous book How To Grow More Vegetables. This involves closer spacing, thinning techniques, and stagger-planting rather than row cropping, which makes the most of space not utilized in row cropping.

A method like this can help growers produce a lot more food in a smaller space while minimizing weeding and mulching with closer spacing; all while still making it an efficient work space for growers. Again, mechanized agriculture doesn’t combine well with biointensive, save for during the tilling and bed-prep phase – all weeding and cultivating must be done by hand. Then again, the technique itself is designed to prevent labor put into weeding or mulching, and is well-suited for smaller operations – particularly for vegetable growing.

RAISED BEDS

Moving up from the ground level, raised beds are another option for your greenhouse hobby or operation. These involve large containers placed on top or above the soil – usually of rectangular or square shape, though this can vary – and then filled with the soil medium of one’s choice. Within this container, plants are then grown: ranging from vegetables to flowers, herbs, annuals, perennials, and more.

Raised beds are best suited for those wishing to grow in smaller operations and greenhouses, and who have no need (or don’t want to use) mechanized agriculture. They can be constructed from wood, UV-safe plastic, metal, or other materials. 

These provide a couple advantages: if beds are made high enough, they reduce back strain during the weeding or working process; on the other hand, they provide a great growing medium for greenhouse growers unable to work or use the soil straight under their covers for whatever reason. It can also give growers more control over the soil mediums they use, instead of being limited to simply what’s available underneath their structure.

SQUARE FOOT GARDENING

Square foot gardening is a popular growing method that combines flawlessly with the raised bed. Much like biointensive growing, it involves close spacing for the benefit of growing more in a small space; it’s biggest difference is that it incorporates companion planting. Ideal for those growing vegetables, herbs, and flowers, hobby growers who only want to grow small amounts in their greenhouse may take interest in this method.

CONTAINERS

For specific kinds of plants – and for greenhouse growers with ambitions to grow at a larger scale – container planting may be just the way to go. This especially applies to ones that don’t need certain cultivation techniques to thrive, but which are also better having their root systems isolated from others nearby (or which are set to be sold individual and separately, such as flowers). Large perennial plants, flowers, nursery trees, shrubs, ornamentals, berries, and even growing cannabis works great with the individual container method, and especially if you want to grow these in great volume.

Not only does container growing prevent weed pressure completely, it can also grant more disease suppression and control over pH, which is especially beneficial for particular plants. Container growing also gives farmers the opportunity to transport their crop quickly and easily when need be, and cater more to the finnicky soil needs of pickier crops. 

Further, containers (much like raised beds) give growers more control over their soils or other growing media they choose, and what goes into them – especially if the natural medium found under the cover is not viable enough for what they wish to grow.

SOIL

Soil is the most likely medium you will find in a container planting setup. Depending on the specific plant chosen and its particular needs, soil can then be cut or combined with other materials that alter the particular drainage, pH, fertility, and other particulars that container plant requires. Soil can either be microbially active, or sterile – if active, this typically means that it has been cut with compost.

PEAT MOSS

Peat moss is a very common additive to most commercial soil mixes. It lowers pH (raises acidity), thus making it ideal for plants that love acidity and commonly enjoy the container life: shrubs, berries, nursery trees, and others. For plants that like damp soils, peat moss helps retain and hold water to prevent excessive drainage.

VERMICULITE

Like peat moss, vermiculite is added to soil mixes for containers to improve water retention. In terms of pH, however, it leans more on the alkaline side of the scale. It comes in either a rough, large texture for larger potted plants, but can also come in a very small, fine texture as well – making it a great option for very small containers, such as for seed starting trays or transplants.

PERLITE

Mined from volcanic rock, perlite is also designed to help retain water in soils. Since its retention rates are higher and better than vermiculite or peat moss, it tends to be added to soils ideal for plants that prefer dampness. It has no nutrient value but is slightly alkaline in pH.

BARK

Typically sourced as by-product from lumber mills (and mostly from pine trees), bark is added to some soil mediums for the purpose of aeration and compaction prevention. It’s definitely on the acidic side of the pH scale. Before it’s added to any soil mixes, however, it must be composted to some extent, because its acidity can be phytotoxic and detrimental to other plants.

COMPOST

Some soil mixes come with substantial amounts of organic matter, or can be completely organic matter – namely, compost. Commercial mixes may include it, or one can cut their pre-made soil mix of other materials with compost to make it more nutritive and microbially-active. 

Keep in mind to never put fresh (or “hot”) compost in a soil mix, or uncut with other matter or in mixes in incredibly high amounts. The high nitrogen content can “burn” your plants, and even kill them. Use finished compost only!

COIR PITH

A fiber extracted from the husk of coconuts, coir pith can be used similarly to peat moss as a replacement and water retaining material. It’s also environmentally friendly and sustainable, which gives it some edge. Be aware that it has a high pH (alkaline) – and be careful about where you source coir from, as some have been found to be high in fungal contamination. 

VERTICAL SYSTEMS

When growing certain types of plants – and raised beds, biointensive planting, or square foot gardening won’t apply as space-intensive methods – you may want to consider vertical systems. Obviously, these will be the best choices in your greenhouse for vining plants like squashes, melons, hops, beans, and indeterminate tomatoes. But in some cases, you can build vertical systems – such as shelfs, water shelfs, terraces, or even intricate irrigation systems – for just about any plant you like: from strawberries and herbs, to lettuce, carrots, and more, so you can grow more in the same amount of space.

HYDROPONICS

Some plants flourish exceptionally in soil-less mediums that involve just water. Hydroponics, the name for water growing methods, allows growers to skip soil altogether and grow healthy plants in water mediums, such as in flood tables. Greens and shallow-rooted plants like lettuce, arugula, strawberries, watercress, and spinach are very successful; while proponents of the method state that its far superior to soil because you have more control of nutrients, and plants grow faster unimpeded by soil limitations.

AQUAPONICS

Aquaponics, while sounding very similar to hydroponics, does have similarities – but it also has its differences. It’s a complex yet sophisticated closed system that brings in the benefits of aquatic life into your growing operation: namely, fish. 

Water used to irrigate all plants (as in hydroponics) actually comes from a pond, aquarium, or reservoir that holds aquatic life, and thus holds their nutrient-rich, highly desirable fecal matter as a fertilizer to them in the process. It should be noted that plants are not directly exposed to the actual reservoir holding the fish and fecal matter (which would harm the plants). Rather, the plant and aquatic life systems are separate, with water from the aquaponics feeding into the hydroponic system.

WHICH MEDIUM WILL YOU CHOOSE?

It all comes down to what you want to grow. Do perennial plants, flowers, shrubs, or even cannabis interest you? Do your plants have picky needs? Then you may want to plant in containers.

Wanting to pump out the produce for a large operation in your space-, cost-, and climate-efficient greenhouse? Invest in something large, and try row-cropping. If you take a particular interest in shallow-rooted plants, then hydroponics may be up your alley.

Or perhaps you’re just a humble hobby grower, with the desire to grow as much as you can in a small space. You might prefer quaint raised beds, combined with biointensive planting, square foot gardening, or even a vertical system for vining plants. Whatever you choose, all mediums are compatible with your greenhouse growing operation.

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CHOOSING A GROWING MEDIUM FOR YOUR GREENHOUSE
Lucija Johum 20 December, 2021
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