Choosing potting composts and using water wisely

IT is important to distinguish between the compost we make in our compost heap from garden and kitchen waste and the composts we use for potting up seedlings and young plants and filling containers and hanging baskets. Garden compost is generally not suitable for use in containers for potting seedlings and young plants, due to the potential for fungal diseases.

With the sale of multi-purpose composts containing peat due to be banned for amateur sales in 2024, and brands needing to find alternatives to peat, the challenge is on to find a suitable substitute.

Sphagnum moss peat, as opposed to the darker, more decomposed sedge peat found on the Somerset Levels, has been the ideal growing media for the last 40 years or more, taking over from the loam based composts devised by the John Innes Institute in the 1930s.

Sphagnum peat is sterile, contains very little nutrients, holds water yet has a structure that allows good drainage leaving air spaces – what we call “air filled porosity”. It is interesting to note that commercial growers will not be banned from using sphagnum peat-based composts, as no really satisfactory alternative is currently available.

This leads one to surmise that amateur gardeners are facing a lottery of which compost to purchase. So, what materials go into composts as alternatives to peat?

For many years coir fibre has been promoted. This comes from coconut husks and must be imported and as such is not a very sustainable product. Those who have tried growing in coir composts will probably agree it is far from ideal. Water flows straight through, but combined with other materials it is often used.

Wood fibre is being increasingly used. Old pallets are broken up, shredded, and composted to make a fibrous medium which again is best mixed with other products. This material is often the cause of tiny toadstools appearing in your pots and trays, as the wood fibres are broken down by fungi. These are usually harmless to the plants but cause concern to gardeners who see them.

Composted shredded bark is proving one of the most useful materials and one which is certainly sustainable. It has many of the ideal properties of sphagnum moss peat, holding moisture, but draining to leave good air spaces. Trace elements and major nutrients are added.

Composted green waste (CGW) is made from the contents of your green bin/bag. It is shredded and composted to high temperatures hopefully to kill off seeds, pests, and diseases but the composting process may not degrade weedkiller residues, particularly the selective weedkillers used on lawns, and I have experienced several cases of hormone weedkiller damage on plants growing in a compost containing CGW.

So, I am very wary of branded composts that contain it. I would like all compost brands to declare on the bag what it contains.

Wool waste is another material making an appearance in potting composts, sometimes mixed with bracken and comfrey, claiming that there is no need to feed your plants. I think this is rather a rash statement, the nutrients will certainly be very slowly available to plants as they are broken down into the basic chemicals that plants are able to absorb.

This may be fine for short term crops such as tomatoes, but for longer use I have reservations.

Although February was unusually dry this year, we still recall the very wet spell before Christmas and last summer’s drought, so planning for watering in case of anther dry year is important.

Water butts are excellent but have a nasty habit of being empty when water is required and overflowing during rainy periods. So, understanding how, and when to water will enable gardeners to use this precious resource carefully.

Plants in containers need to be kept moist by hand watering, or using one of the many automated dripper systems which work extremely well. Plants in the ground can vary in their demand for water.

Newly planted trees, shrubs or perennials will all need to be watered during their first year of establishment. Transplanted vegetables and bedding plants need care during their early days, whilst their roots explore the soil. Thorough watering after planting and the addition of a 5cm (2”) surface mulch will help enormously.

Vegetables vary considerably in their demand for water at different stages of their growth cycle, so an understanding of this will enable valuable water to be applied where and when it is most needed.

Leafy vegetables like spinach, lettuce and cabbage need a constant supply, although cabbages are more tolerant than the others. Root crops, such as carrots and parsnips, tend to split if they are dry for any period and then the rains come.

Runner beans need water at the point of flowering and bean development. However, French beans are much more tolerant of drought and are also self-fertile so they set a good crop even if the bees are having a holiday.

The hybrids varieties of Moonlight, Firestorm and Snowstorm are runner beans with French blood, making them the perfect combination for a reliable crop. They grow, look, and taste like runner beans.

Potatoes need water when the baby spuds are roughly the size of marbles. The most cantankerous vegetable to grow is the cauliflower. The slightest check in their growth at any stage results in premature curding and failure. Leave them to the experts and buy the “imperfectly tasty” ones from your grocer.

The one vegetable that is the most adaptable and rarely needs water is the humble beetroot, easy to grow, rarely attacked by pests (other than mice and badgers) and diseases, and they are apparently so good for us. They now come in a variety of colours, and even pink and white stripes to suit all tastes. Roasted, boiled, and even shredded and eaten raw, the humble beetroot beats them all.

• If you have raised your own plants and your greenhouse is unheated, keep the plants on a bright windowsill indoors for a few more days.

• Sweet corn can be sown in cell trays inside but delay planting out until next month.

• Marrows, courgettes, pumpkins and squashes can be sown in individual pots towards the end of the month. These will need protection if sown outside. Peat pots are very good for this.

• Consider buying a cold frame to ease the strain on space in your greenhouse at this time of the year. It is ideal for hardening plants off prior to planting them outside.

• Plant main crop potatoes. Early varieties may need earthing up to exclude the light from the tubers. Cover shoots with fleece to protect from frost damage.

• Sow more peas and broad beans. Support early sown varieties. Make a first sowing of French beans towards the end of the month. Sow runner beans in pots inside.

• Sow vegetable varieties that have inherent pest and disease resistance.

• Sow perpetual spinach, leeks, radish, turnips, lettuces, carrots, beetroot, Swiss chard and summer cauliflowers outside.

• Protect flowers on peaches, nectarines and apricots from frost. Use a soft brush to hand pollinate blooms and increase chances of a good crop.