Ignore at your peril: Seeds of things to come

'And now," cried Max, "let the wild rumpus start!" It's at this time of the gardening year that I start to feel like that little boy in Maurice Sendak's Where the Wild Things Are. The garden, meanwhile, reminds me of a giant firecracker whose fuse has been lit; any moment now and I know that it will start to soar skywards in a spine-tingling, unstoppable explosion of light and colour, leaving me scrambling to catch up. And while I promise myself every year I'll be fully prepared for that sudden magical surge of growth, for that moment when you realise that spring has finally sprung, inevitably I'm not.

Not that our gardens give a fig whether seeds are sown, dahlias are potted, or chitted potato tubers are carefully tucked down deep into the cool earth on time. But if you want a summer garden or allotment full of food and flowers, now’s the time to put the work in. This is especially true when it comes to the spring ritual of seed sowing, where there is a window of opportunity that all gardeners – but especially those who like to grow their own food – ignore at their peril.

Undercover gardening

Unless your garden or allotment is an exceptionally warm or sheltered one, it's still a little too early in the year to sow most things outdoors. Exceptions include potatoes, onions, shallots (the last two as sets) and broad beans. But if you have a sunny porch or conservatory or polytunnel or glasshouse, then you can give many others a wonderful head-start by sowing the seed under cover over the coming weeks, for transplanting outdoors later in the year as young module-raised plants. The list of suitable plants includes leeks, cabbage, cauliflower, Brussels sprouts, beetroot, annual spinach, Swiss chard, scallions, spring onions, kohl rabi, rocket, lamb's lettuce, lettuce, borage, parsley, dill, coriander, fennel and alpine strawberries . Flowering annuals too, including pot, French and African marigolds, sweet pea, Ammi visnaga and A. majus, cornflowers, the inky-flowered Cerinthe major, Cosmos, sunflowers, silky petalled Malope "Vulcan" and Malope "Alba", lacy Orlaya grandiflora, perfumed Nicotiana, peacock-blue Salvia patens and S. viridis and the daintily pretty "Love-in-a-mist".

Plants that can be sown over the coming weeks for growing on later in the year under cover of a glasshouse/polytunnel/ sunny conservatory include tomatoes, chillies, peppers and aubergines (but hurry), as well as dwarf and climbing French beans, cucumbers, sweetcorn, melons and courgettes.

Some gardeners will baulk at this, arguing that raising young plants under cover in this way is too much work. But the truth is that you will save yourself a lot of time, effort, seed and disappointment by doing so. Germination rates are higher, faster and more consistent than for seed direct-sown outdoors, while vulnerable young seedlings don’t have to compete with weeds, wildly fluctuating temperatures or less-than-perfect soil. Pests and diseases are also much less of a problem.

Occasionally I meet gardeners who tell me that they’ve had little luck with raising plants this way. Almost always the problem is one of inadequate heat, as seed sown into cold, sodden compost is more likely to rot than to germinate. As a general rule (there are exceptions), the seed of most plants germinates best in an average, steady soil temperature of about 21 degrees, while some – tomatoes, peppers, chillies, aubergines and melons, for example – like it even hotter. And so it’s well-worth investing in one of the small electric propagators stocked by most good garden centres at this time of year. Recommended online Irish stockists include mrmiddleton.com, johnstowngardencentre.ie and quickcrop.ie.

Along with inadequate heat, poor-quality seed compost is another cause of low germination rates, especially as regards many of the peat-free brands. So use a high-quality product, such as the German-manufactured Klassmann Organic range, stocked by online Cork-based suppliers fruithillfarm.com , which includes both peat and peat-free options. Fruithill Farm also stocks hard-wearing, high-quality plastic propagation trays and plant pots that will give many years of use.

Other tips are to avoid sowing too thickly or too deeply. Also gently water the compost both before and after sowing with tepid water using a fine spray, and cover seed trays with a transparent lid/ cling film to encourage a warm, humid atmosphere.

Early care

Once your seedlings have germinated, it’s all about ensuring their growth continues. Seedlings left too long in a tray compete with each other for light, water and nutrients and become vulnerable to disease, so prick them out into modules or individual small pots filled with potting compost once they’ve developed their first set of true leaves. Keep the compost adequately watered (damp but not sodden), using tepid water to avoid shocking tiny root systems. Make sure to give seedlings and young plants plenty of light, and protect them from chilly draughts or extremes of temperature. On very cold nights, temperatures can quickly plunge, even indoors in an unheated room so, if in doubt, use layers of fleece.

Conversely, on sunny days, temperatures in a polytunnel, glasshouse or conservatory can soar and they will need to be ventilated. Nor should you move heat-loving plants such as peppers, chillies,aubergines, cucumbers and melons into an unheated glasshouse or polytunnel until at least early May. All of this may sound like a lot of work, but the result, I promise, will be a summer garden heaving with delicious produce and flowers.

THIS WEEK IN THE GARDEN…

Plant early varieties of potatoes

Examples include Lady Christl, Charlotte, Nicola, Red Duke of York. Space the tubers 25-30cm apart, with 45-50cm between rows. Potatoes like a free-draining, very fertile, deep soil in full sun, enriched with well-rotted manure.

Turn over the compost heap

Exposing the material to oxygen helps jump-start and reactivate the process of decomposition, which will have slowed down considerably over the winter months. If the heap smells sour, mix in some carbon-based materials (fallen leaves, straw cardboard) and some fresh, nitrogen-rich material (vegetable peelings etc) and then add a biological activator such as Compost Renew (Bateriosol) which will help accelerate the process by stimulating bacterial activity.

Find a corner of your garden or allotment to plant a patch of comfrey (Symphytum x uplandicum)

Once established, the leaves of this fast-growing perennial can be harvested three or four times during the growing season. It can be used to make a potash-rich liquid feed for hungry plants, laid at the bottom of potato drills, treated as a mulch or added to the compost heap. The best variety is the sterile “Bocking 14” (pictured above). Comfrey is happy in sun and semi-shade and likes a rich, moisture-retentive soil.