Have you noticed the price of potting soil these days – crikey! Filling up containers isn’t cheap, and it can cost a small fortune to fill raised beds.
So how can we eke out potting mixes and save big on composts? Watch our video or read on to discover five simple solutions, including crafty ways to scrimp on potting mixes, reuse them and – my favorite – create new beds for next to nothing!
1. Fill Pots for Less
It never ceases to amaze me how quickly I can get through bags of potting mix, especially early on in the growing season. But ask yourself: Do you really need to fill all of your containers with pricey potting mix?
Many shallow-rooted crops like lettuce, radishes and strawberries can cope in soil as shallow as 6 inches (15cm), so there’s little point in having expensive potting mix below this depth. Instead, start filling containers with free materials to bulk things out: chopped up sticks and twiggy material, old leaves or straw.
For heavy feeders such as squashes and cucumber a great option is to part-fill containers with nutrient-dense materials such as kitchen scraps or the freshly cut leaves of nutrient accumulators like comfrey.
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Use this root depth table to help work out how much potting mix you actually need
2. Reusing Potting Soil
Old potting mix can be used to part-fill containers below fresh potting mix as described above, or you can rejuvenate it – there’s life in the old potting mix yet!
Start by dumping out old potting mix from containers into a wheelbarrow or onto a tarp to dry out a little. Once it’s dry, pick out any large bits of root left behind by the plants grown in it previously. There’s no need to be too fussy about this because the scraps of root will gradually rot down and release their nutrients into the mix. Remove any other plant debris, then store in lidded containers or bags until you’re ready to use it.
To revive your old potting mix, add an equal volume of new potting mix and a handful or two of organic fertilizer such as blood, fish and bone, or a vegan alternative. Mix it all together thoroughly.
Reusing old potting mixes does carry the risk of passing on soil-borne diseases, but you can minimize this risk by using potting mixes you grew edibles in for growing flowers the second time round, and vice versa. Don’t reuse mixes if they contained heavily diseased plants.
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Growing flowers in old potting mix helps avoid crop rotation conflicts
3. Make Potting Mix Go Further
Both new and rejuvenated potting mixes can be made to go further using either garden-made compost or sand, depending on what you plan to grow in it.
Rich, dark compost is a fantastic source of goodness for heavy feeders, so mix sieved compost into your potting mix to create an extra-rich growing medium for these hungry plants. Potatoes, squash family crops, tomatoes, and brassicas such as cabbages are just a few examples of crops that will relish the moist, nutrient-heavy environment this should create.
Conversely, some other vegetables grow better in a less rich soil. Carrots, for example, will happily grow in potting mix cut with sand to create a very free-draining growing medium. Cheap builder’s sand works just as well as horticultural sand, or perhaps you have an old sand pit that can be plundered. Mix the sand with equal parts potting mix to make a fantastic growing medium for root crops.
You can also make your own potting mix from scratch. It can work out cheaper, and is very easy to do. You can find out how in this video.
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Compost kitchen scraps directly in the ground to directly enrich the soil
4. Make Compost Pits
Adding kitchen scraps to a compost pit or trench in autumn or winter is a superb way to save on bought-in composts.
Rather than add finished compost on top of the soil surface, instead dig out a hole and set aside some of the soil. Tip a good layer of kitchen scraps into the bed, before covering it with the excavated soil. The kitchen scraps will rot down over the course of the winter, leaving a deliciously rich, moist layer for the roots to grow down into.
5. Fill Beds for Free
And now for my favorite tip to save your hard-earned money: filling raised beds or building up new planting areas for free!
An easy method to create new beds is to use the ‘lasagna’ technique, which uses layers of organic material to create your growing medium. You can add a frame to your bed if you want to keep it tidy, but that’s not essential.
Lining the bottom of the bed with a few layers of cardboard will help to kill off any grass or weeds. Give the cardboard a thorough water to dampen it before layering up your lasagna ingredients. You need alternating layers of carbon-rich ‘brown’ materials and nitrogen-laden ‘greens’, starting with a 2-4 inch (5-10cm) layer of browns such as straw. Top it with a layer of greens such as spent crops or grass clippings, then add another layer of browns and then more greens, and so on. You should end up with a bed that’s at least 18in (45cm) high, but ideally deeper than that if you have enough materials to hand. If it’s dry, water regularly to help all that organic matter begin rotting down.
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Lasagna beds came be made free-standing (as shown at the top of the page) or contained
Your lasagna bed may look huge at first, but it will slump down within a matter of weeks. Autumn or early winter is a great time to start off new beds this way, as the repeated freezing and thawing of winter should help break it all down, ready for planting in spring. If it hasn’t completely broken down by then, you can just finish off with a couple of inches of garden compost, then plant into that.
An alternative to the lasagna method is to build up a deep bed with prunings, progressively moving from larger logs to smaller sticks and twigs, before finishing off with plant waste such as dead leaves, and then compost or potting mix to cap it off. The other bonus of this is that as the woodier material slowly breaks down it releases back the nutrients it contains to feed your plants, much like a slow-release organic fertilizer.
