Composting, How To, Jorge, Planters, Planting

The amount of compost needed for a planter depends both on planter size, its material and the plant you wish to grow. Compost is important as it will improve your soil’s structure, increasing its available water capacity (AWC), which is especially important for planters. Calculating a planter’s volume (measure in litres) is relatively easy, but it is first important to work out the compost/garden soil ratio required for a particular plant.

Compost/Garden Soil Ratio

Now why do I want to mix compost with garden soil? Firstly, garden soil is incredibly complex with numerous soil organisms that help boost your plant’s health. These organisms will help improve the structure of your soil and break down organic matter into mineral nutrients, available for uptake by plants. However, there is the possibility of inducing pests and diseases, so we recommend avoiding soils that you have previously planted. Secondly, garden soil will help improve drainage, ensuring your planter does not become waterlogged. Lastly, using garden soil will save you money and lower your environmental footprint.

While compost does add nutrients to the potting mix, its major advantage is improving the water-holding capacity of the soil, which occurs through two mechanisms. Firstly, compost contains carbon, as well as other nutrients, that provide food for soil organisms. These organisms function to increase a soil’s porosity – the percentage of soil that is pore space or voids. Secondly, compost improves soil structure by gluing tiny particles of rock (sand, silt, or clay) together into peds (aggregates), which is the basis of all good soils. These peds have adequate pores to allow entry of air and water, both which are essential to plant health. The increased porosity has its origin in the fact compost is significantly lighter than conventional soils.

An ideal soil has a porosity of about 50%, equally divided between micro and macropores, which provides a good mix of drainage and retention. When it rains both macro and micropores become filled with water. Larger pores are the first to drain with light sandy soils taking about a day and heavy clay soils about three. Micropores remain filled and are unaffected by gravitational flow, the water held by electrostatic attraction. The smaller the pore, the more tightly the water is held. Macropores drain too quickly to be of much use to plants, providing little water, but allowing flows of oxygen to plants’ roots. Micropores retain water, available for use by plants. Hence, macro and micropores complement each other, allowing air and water to reach plants’ roots.

Picture credit: MesserWoland licensed under CC BY-SA 3.0.

Fascinatingly, small pores act to draw groundwater up through the soil, providing a source of water in the absence of rain. This phenomenon occurs due to the forces of cohesion (propensity of water molecules to stay together) and adhesion (propensity of water molecules to stick to other surfaces). When the force of adhesion is greater than that of cohesion the water rises, with the water near the edge of pore curving upwards. Capillary action can be easily demonstrated by dipping a paper towel in water and watching water climb the towel.

Soil textures – clay, sand, silt and loam – each have different drainage profiles, originating from the size of the particles. Clay particles are the smallest, sand the largest and silt in between. The larger the average particle, the faster the soil drains. Loam is comprised of about 40% sand, 40% silt and 20% clay and is considered the best texture, having the optimal balance of micro and macropores. Clay lacks larger pores, providing poor aeration and drainage, and possesses minute micropores too small for plants to utilise, reducing the soil’s available water capacity. Sand, on the other hand, drains too quickly, predominantly composed of large pores.

Compost increases the number of micro and macropores in the soil, greatly improving a soil’s available water capacity, and should be added to all soil textures including loam. B. D. Hudson’s 1994 paper demonstrated that for every texture as organic matter was increased by 1-3%, the available water capacity doubled. A 2000 study by A. Maynard found that the amount of water in a plow layer (8 inches) increased from 1.3 to 1.9 inches in soil amended with compost, providing a two week supply of water for vegetables, significantly reducing water stress.

An increase in the available water capacity is especially beneficial for potted plants that receive significantly less rainfall due to their container’s small surface area. We recommend the potting mix contain 20-50% compost with higher blends if your soil is clay, your plant thirsty, or the planter’s material porous as with terracotta. Compost will not provide all the nutrients needed, so we recommend the application of organic fertiliser. Mulching is also useful and will help improve water retention and soil structure.

Calculating Volume

A 1 litre cube. Picture credit: H McKenna licensed under CC BY-SA 2.5.

Volume is the sum of 3 measurements (length, width and depth) multiplied together and is expressed in cubic units (cm³, m³). Cubic units correspond directly to litres with 1 litre equal to 1000cm³.

Most planter retailers will give you the dimensions of a planter in cms that can be used to calculate volume. In not, you can use a tape measure. Compost is sold either in litres (l) or cubic meters (m³).

Note: most planter dimensions provided online will be the outer rather than inner dimensions, so you’ll need less compost, depending on the thickness of its sides.

Note 2: planters come in a huge range of shapes. Hypothetically you can calculate the volume of any shape (done by dividing shapes into smaller ones), but we recommend you simply approximate the shape.

Once you have calculated your planter’s litres, simply times it by 0.2-0.5, depending on how much compost you wish to add, to arrive at the quantity you need to buy.

Cubes and Rectangles

Calculating volume for cubes and rectangles is very easy. Simply multiple width, depth and height and then divide by 1000.

Hence, a 100cm³ planter would have a volume of 1000 litres. (100 x 100 x 100 / 1000.) A 140 x 30 x 30 rectangle would have a volume of 126 litres. (140 x 30 x 30 / 1000.)

Cylinders

Calculating the volume of a cylinder requires multiplying height by radius squared by pi which is written as V =πr²h. You then need to divide by a 1000 to get volume in litres. Hence a planter with 30cm diameter and 30cm in height would have a volume of 21 litres. (3.142 x 15² x 30 / 1000.)

Bowls

To calculate the volume of a bowl, you have to calculate the volume of a sphere and divide by 2. Calculating the volume of a sphere requires multiplying 4 divided by 3 times pi times radius cubed, which is written as 4/3πr³. You then need to divide by a 1000 to get volume in litres. Hence a bowl with a 15cm radius would have a volume of 7 litres. (((4/3 x 3.142 x 15³) / 1000) / 2.)

If you would like to know more about soil science please read our guide: Everything you need to know about soil.

If you are interested in pots, Primrose has the biggest range online with over 2000 planters. We also sell compost starting at £5.99.

Jorge at PrimroseJorge works in the Primrose marketing team. He is an avid reader, although struggles to stick to one topic!

His ideal afternoon would involve a long walk, before settling down for scones.

Jorge is a journeyman gardener with experience in growing crops.

See all of Jorge’s posts.

Flowers, Gardening, Gardening Year, George, Grow Your Own, Herbs, How To, Infographics, Planters, Planting, Plants

You may have noticed over the last few months that we’ve been going potty over pot-growing plants. Through a series of infographics, we’ve compiled the Complete Guide to Container Gardening – simple guides to help you get the most out of planting in pots.

Here are the collected guides for you to enjoy all over again. And when you’re ready to start growing, we have all the planters you could ever need!

How to Plant in Pots

How to plant in pots

We kick off with the basics, for gardening novices or simply those who need a refresher. Planting in pots opens up a whole world of flexible gardening for decorative plants, herbs, houseplants and more.

How to Repot a Plant

Hot to repot a plant

Most potted plants will need repotting at some stage in their life. If they outgrow their current container it’s essential to give them more space. We made this 5 step guide to make the process super straight forward!

How to Water Pot Plants

How to water pot plants

Watering is one of those critical conundrums when it comes to pot plants. With potentially no natural water and limited drainage, it’s easy to over or under-water. Follow these best practices for healthy plants.

How to Choose the Right Planter for Your Garden

How to choose the right planter

Picking the right planter is a deceptively easily task. But there are so many factors aside from taste – material, portability, size and more. We address them all to make your decision simple again.

How to Plant Potatoes in Containers

How to plant potatoes in containers

Container gardening is such an adaptable form of growing and it’s perfect for raising your own crops to eat. Potatoes especially are a natural fit for pots, meaning you can have home-grown spuds without the need for an allotment.

How to Plant Strawberries in Containers

How to plant strawberries

Strawberries are perfect for growing in pots on the patio too. Fresh fruit on the doorstep – what’s not to like? We take you through how to grow the juiciest strawberries at home.

How to Grow Herbs in Pots

How to grow herbs in pots

Take your cooking to the next level with a stock of fresh herbs at your fingertips. We show you how to start growing herbs at home in a kitchen garden or right on the windowsill.

How to Grow Plants Indoors

How to grow plants indoors

Of course, many of us who love container gardening do so because it allows us to fill the house with beautiful blooms. Indoor gardening has its own challenges, so we’ve got the tips for you to master it.

How to Plant a Hanging Basket

How to plant a hanging basket

Finally we round off the series by heading back out into the garden for a classic horticultural endeavour – planting a hanging basket. By now you should be an expert in container growing and well prepared for this last task.

George at PrimroseGeorge works in the Primrose marketing team. As a lover of all things filmic, he also gets involved with our TV ads and web videos.

George’s idea of the perfect time in the garden is a long afternoon sitting in the shade with a good book. A cool breeze, peace and quiet… But of course, he’s usually disturbed by his energetic wire fox terrier, Poppy!

He writes about his misadventures in repotting plants and new discoveries about cat repellers.

See all of George’s posts.

Celebrations And Holidays, Competitions, Current Issues, Decoration, Events, Flowers, Garden Design, Garden Furniture, Gardening, Gardening Year, Hampton Court Flower Show, Liam, News, Planters, Planting, Plants, Ponds, RHS, Water Features

The Primrose team attended this year’s RHS Hampton Court Palace Flower Show to catch up with and discuss the latest gardening trends as well as engage with some of the nation’s favourite horticultural festivities. We endured the sweltering heat and odd glass of champagne to hopefully bring you the inspiration for your perfect garden.

Tropical

On display at this year were a vibrant showcase of exotic landscapes seemingly plucked from some far-off jungle and dropped onto the grounds of Hampton Court Palace. However, tropical gardening is something which is growing in popularity in the UK and not just the odd palm tree.

Tropical plants are, in fact, surprisingly hardy and many of them can tough it out through a British winter. Creating a tropical aesthetic in your very own garden provides a sense of exotic escape in what can be an otherwise cold and stressful routine. More and more urban dwellers are looking to bamboos, ferns, sarracenias and zantedeschias to create these backyard get-aways.

Many of these tropical varieties are used to battling it out below the canopy for little light and nutrients and so can thrive even in the heart of the concrete jungle. For gardens everywhere tropical planting offers height, depth and an abundance of life. Water-features and lighting perfect the ambience offering various tones and sounds.

Prairie Planting

A major trend at this year’s show was Prairie Planting; the combination of wild flowers and grasses in a seemingly loose planting scheme. Pockets of meadow teeming with wildlife were a persistent feature offering a wholesome, wild but almost gentle beauty.

There are an abundance of prairie plants which are native to the UK all of which are hardy enough to thrive in poor soils in times of drought and frost. Therefore, they make a perfect low-maintenance garden with a more natural aesthetic. Eryngiums, Echinaceas, Achilleas and Salvias among others offer a rich pallet of colours while various grasses deliver height and texture.

The prairie garden is also a fantastic way for you to join the noble crusade of saving our native bee and butterfly populations. Already an incentive which is sweeping  the country, prairie patches are being planted in local initiatives to save our ecosystems. With some bordering and creative features thrown in prairie planting also helps make an award-winning garden too.

Reclaimed

Here is a trend which certainly taps into the prevalent vintage culture of today. Adding a certain character to outdoor spaces it creates a more relaxing atmosphere allowing the mind to wonder amongst the assortment of bizarre objects strewn across the flower beds.  Big concrete planters, weedy patios, even bits of recycled car parts and vintage furniture make an appearance.

Once the hardware is in the garden is certainly easier to manage than a pristine and strictly coordinated garden while keeping a sense of style and purpose. Ground covering and climbing plants are encouraged to grow over. One may find a bike wheel or an old Coca-Cola sign amongst the wild grasses. There is certainly space to let your imagination roam.

Along with prairie planting, Rust was a consistently strong contender throughout the show and the reclaimed aesthetic is a natural ally to both these features.

Jorge at PrimroseLiam works in the buying team at Primrose. He is passionate about studying other cultures, especially their history. A lover of sports his favourite pass-time is football, either playing or watching it! In the garden Liam is particularly interested in growing your own food.

See all of Liam’s posts.

Flowers, Gardening, George, Grow Your Own, How To, Infographics, Planters, Planting, Plants

Hanging baskets are a staple of garden design – both traditional and modern. They’re brilliant at brightening up walls or framing your front door with a burst of colour. So don’t delay – read our guide to learn how to plant a hanging basket and master this essential gardening art.

Head over to our shop to see our range of hanging baskets.

How to plant a hanging basket infographic

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Designed once more by our graphic designer Becky.

This is the final part of our Complete Guide to Container Gardening! Check out the previous installment, How to Grow Plants Indoors or flick through them all over again from the beginning with How to Plant in Pots.

George at PrimroseGeorge works in the Primrose marketing team. As a lover of all things filmic, he also gets involved with our TV ads and web videos.

George’s idea of the perfect time in the garden is a long afternoon sitting in the shade with a good book. A cool breeze, peace and quiet… But of course, he’s usually disturbed by his energetic wire fox terrier, Poppy!

He writes about his misadventures in repotting plants and new discoveries about cat repellers.

See all of George’s posts.

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