Whether growing herbs in sprawling gardens, dedicated allotments or on windowsills, the verdant and edible blooms require the same maintenance and care. From regular watering, pruning and dusting to ensuring proper drainage and un-tangled roots, the most important way to ensure a prosperous yield starts with the soil.
We spoke with the RHS-trained Horticulturalist and dedicated Plant Doctor for Patch Pants, Kelly, for some insight into the different types of soil and what works best for indoor plants.
What are the different soil types?
“Unlike the different soil types that you get outdoors, which are heavily influenced by the topography of the landscape (i.e. chalky, sandy, loamy) the general purpose potting compost that you get for indoor and general household plants has been fine-tuned to create a neutral pH with a balance of minerals and a blend of free-draining and moisture retentive particle sizes,” explains Patch’s dedicated Plant Doctor.
Kelly goes on to explain the composition of common household soil, “For the most part potting compost includes a blend of moss/peat, organic matter (broken down vegetation), bark, perlite and vermiculite. Some potting composts include man-made slow-release plant food in the form of osmocote.”
The Plant Doctor also explains why so many soils and composts have ‘Peat-Free’ emblazoned on the packaging, “Up until recently most potting composts have included peat, which is known for being highly moisture retentive, but as awareness increases around the precious, non-renewable nature of this resource, there is a commitment to moving away from its use and to seeking suitable alternatives. One of the main substitutes is coir, or coconut husk fibre.”
“Houseplant-specific potting compost is likely to be more free-draining than general purpose potting compost, and special mixes for plants like orchids or cacti and succulents, are likely to be even more free-draining again,” Kelly explains. “What makes a compost mix more free draining are bigger, less ‘sticky’ particle sizes like sand or bark. While most plants enjoy a neutral to slightly alkaline pH (all general-purpose potting composts), some plants need more acidic soil, and you’ll need to invest in ericaceous compost specifically.”
Why are different soils required for different plants?
“Most leafy houseplants and herbs are happy in a general-purpose potting compost. Plants like cacti and succulents, however, which have adapted to store water in their stems and leaves, need a much more free-draining potting mix or they are likely to rot. A much higher ratio of sand, grit or perlite to organic matter is therefore required, so that some but not too much water is retained,” says the Plant Doctor.
She suggests checking your plant’s specific needs before investing in litres of soil. This can be achieved through handy applications like PictureThis or with a simple Google search. “It’s always good to check if your plants have a particular pH preference. For instance, if you are growing outdoor plants like Acers or Camellias in pots, they require a more acidic or ericaceous compost, and if you're growing plants like lavender in pots, they require compost that is a bit more alkaline.”
What's the best way to maintain soil at home?
“The best way to maintain soil is firstly to add plant food every fortnight or once a month throughout the growing season, from mid-Spring to mid-Autumn. This is when your plants are in active growth in response to the increased light levels and temperature. This tops up the nutrient levels, promoting healthy growth and building up your plants' immunity or resilience to pests and diseases.
“There are a range of plant foods available for different plants, and they will have a different NPK (Nitrogen, Phosphorus, Potassium) ratio depending on what you want to encourage your plant to do. Plant food higher in Nitrogen, for instance, encourages green leafy growth, whereas plant food higher in Potassium, promotes fruiting and flowering.”
How often should house plants be re-potted?
“At some point, your plants will have used up all of the available nutrients in the original soil they were potted into, and despite additional plant food, they won’t be getting all the nutrients they need. This is when repotting is required, and why repotting it’s so important. Fresh compost is also essential to maintain the correct airflow and water absorption around the roots of your plants.
“The general rule of thumb for repotting is every two to three years, but the signs to look out for are:
- If the roots have filled the pot or are coming out of the drainage holes at the bottom of the pot
- If the level of compost in the pot has sunk significantly. This means it’s broken down into smaller particle sizes over time.
- The roots are pushing the plant out of its existing pot
- If your plant has stopped putting on any new growth. This will mean it’s used up all of the nutrients that were originally available in its soil.
- If your plant is drying out very quickly, if the soil has gone rock hard, or if the soil has contracted in from the edge of the pot”
With Plant Doctor Kelly’s advice in mind, we’ve curated a selection of the best soils for prosperous, high-yielding herbs and leafy green houseplants below. Whether you’re repotting or planting anew, keep scrolling for certifiably terrific composts.
Miracle-Gro Performance Organic, Fruit & Vegetable Compost
A go-to, multipurpose fruit and vegetable compost beloved by amateur gardeners up and down the country, Miracle-Gro is a high-performance 100 per cent natural and organic compost formulated for producing tasty and abundant yields. Slow-releasing nutrients keep your plants fed for up to three months at a time for easy maintenance, while helping them to produce twice as much produce.
Buy now £9.07, Amazon
Miracle-Gro All Purpose Enriched Compost
Same, same but different. This all-purpose Miracle-Gro compost is a fantastic choice for those looking to save on gardening supplies for smaller spaces. The nutrient-rich compost can be used for indoor and outdoor potted plants, as well as fruits, vegetables and herbs. It keeps plants fed for an impressive six months, encourages faster growth, stronger plants, maximum root growth and absorbs up to 25 per cent more water.
Buy now £8.55, Amazon
Westland Top Soil
A rich, clay loam soil which is ideal for creating nutrient-rich herb beds, we recommend mixing Westland’s Top Soil with some coarse grit or perlite to improve drainage. A combination of moisture-retentive compost and grit is ideal for thriving herbs at home. This topsoil is mainly used to improve existing soil beds, so it’s a great option for mixing with shop-bought, pre-potted herbs.
Buy now £4.00, B&Q
Organic Peat Free Compost
This environmentally friendly compost mixes fine bark, wood and coconut fibre for nutrient-packed goodness which allows for both moisture-retention and drainage where necessary. It’s RHS-approved and suitable for potted plants, flower beds, tomato plants, vegetables and herbs.
Buy now £8.00, Patch
Melcourt Topsoil Blended Loam
This is another brilliant RHS-endorsed soil - this time a blended loam consisting of sandy loam and organic matter. It’s a fine-textured, free-flowing and incredibly easy-to-handle soil which is brilliant for both domestic and professional use. Since it’s virtually stone-free, mix with grit for better drainage for herbs and plants which require less water retention.
Buy now £12.99, Amazon
Incredicompost Multi-Purpose
A vegan-friendly formula crafted to promote strong flower, foliage and root growth, Incredicompost Multi-Purpose is suitable for both ornamentals and edible plants. Though it contains peat, it includes considerably less than other classic peat soils and is mixed with 20 per cent wood fibre.
Buy now £11.99, Thompson Morgan
Westland John Innes Seed Sowing Compost
For those looking to sow herbs from scratch, Westland’s John Innes Seed Sowing Compost is a top-notch choice. It’s 100 per cent peat-free and enriched with vermiculite to retain moisture and nutrients, making it brilliant for bringing seeds to life speedily and healthily. It’s a light compost, meaning that seedlings can easily push their way through the surface as they emerge. It has a neutral to slightly acidic pH level.
Buy now £9.95, Amazon
