Fiann Ó Nualláin says you can boost the growth potential of your plants by thinning seedlings

May is the thinning month, for the bulk of edible crops — if you want them to bulk themselves up that is. Previously sown seeds may have germinated in clusters or clumps or just come up too close together to get the maximum growth from your crop, so removing all but one or making room for expansion is considered gardening best practice.

Thinning enables space below ground for roots to swell and spread, as much as it provides space topside for foliage spread. Leaving crowded seedlings to continue growing can result in stunted plants as they compete for moisture, nutrients, and light from the same pocket of space.

Crowded plants can have a tendency to increased susceptibility to diseases and even pest attack. All this stress does not induce the most flavourful produce.

So thinning is a good idea but what is the best way to go about it? It is plant disturbance after all and while for decades and more, gardening pundits recommended you pluck out the excess, they rarely mentioned the shock and other jeopardies to the seedlings left behind. I prefer to thin on cool, still days in part as the scent of your thinning can waft on the air and alert every pest in the vicinity to just where your cabbages, carrots or onions are, or to put it another way, to where their favourite munching or laying sites are.

The second reason I like cool and still days is that my own patience is not tested by rushing the job to beat the rain or to avoid my neck being scorched. Attention to detail is as important in the garden as anywhere else and being comfortable is important to diligence, vigilance and focus. The cool and still also means that you can water the row to be thinned a half hour or one hour prior to thinning without fear of leaf scorch.

Just a sprinkle and a short absorption time delay in order to plump up those seedlings and soften the soil at the root zone so you can gently prize out with minimal disturbance to the one left behind. Always gently firm the soil around remaining seedlings and /or water it again.

I know some gardeners who, rather than prize up the excess seedlings, will simply nip out the tops with their nails or a scissors to avoid any root disturbance whatsoever. All I will say is that if your seedlings are in soil then the nip process can leave the roots behind to wither and rot back into the soil potentially also feeding the seedling left behind.

Soil-grown seedlings are often quite sturdy and have beneficial bacteria at their root zone to strengthen the survivor. A wet seed tray, however, or a humid greenhouse row is perhaps more prone to fungal and bacterial infection from rotting material. So apply techniques to circumstance.

Similarly to thinning, disbudding can be a practice of strengthening the vigour of plants for future years or an aesthetic practice to get the most of your roses, camellias or dahlias.

In the edible garden, disbudding is the select thinning out or, in some cases, the removal of all flowers. It is a practice done to manage fruiting yields. We are effectively thinning the flowering buds to control the fruiting capacity of the plant.

Traditionally, new strawberries (those planted earlier in the current year) have their flowers removed preventing them from setting fruit this season and thus focusing their energies on building good roots to support a bumper crop next year. Disbudding is a bit of ‘tough love’ and it is also hard to deny yourself a crop, especial one so delicious.

The solution to that quandary is to get some strawberry plants into a hanging basket and let them be a small crop this year while the other disbudded strawberry plants under your care can be all about next year’s bumper harvest. You can also try some garden-grown, alpine strawberries too, small but wow.

It is not just strawberries that benefit. Peach, pear, apple even quince — in fact, a lot of fruit trees can be encouraged into bigger fruits with some strategic disbudding. Every June, fruit growers experience what is known as the ‘June drop’ where about half of the forming fruits fall off the tree. This is the tree exercising a form of disbudding/thinning on its own yield. So it can better support a more sustainable crop level to full maturity. Disbudding is not limiting your full potential harvest, it is simply helping the fruiters you grow to keep their energies on a good crop.

However, it is not essential and not every grower employs it as a regular technique. I don’t. In reality, not every flower will be fertilised and go on to develop a fruit and not every fertilised flower will survive that late frost or harsh wind. So thinning out your flowers is a bit of a risk. Let the June drop do it for you.

So to ‘pinching out’ — the removal of side shoots or top shoots to encourage a growth pattern. We hear of it most often with herbs, peas and beans and tomatoes. With herbs, pinching out the tops of the plant mimics browsing by animals and the plant in defence puts out more sideshoots and extra growth. We reap the reward of this trick with extra foliage to harvest.

With peas and beans, it not only encourages more side growth lower down and along the plant and thus more flower/fruit-bearing parts, but it also helps remove the growing tip hormones that attract aphids. For a bumper crop, wait until they reach the top of your support and then fire away.

When it comes to tomatoes, there are two main growth habits — indeterminate aka vine or cordon (one central stem) and determinate aka bush type. It will say which on the seed packet or label. How you approach pinching out depends on the type. Indeterminate like a strict training — that’s a pinching out of all the lateral growth (aka side- shoots) and the removal of any competing leader stems. This encourages fruiting trusses rather than leafy foliage expansion.

Later, it is also advised to pinch off the growing tip of the main stem to switch the production of growth hormones to ripening hormones — this is done at a specific position that is different for outdoor cultivation and indoor cultivation.

Outdoor is at two leaves above the fourth truss of fruits — with indoor it is above the sixth truss.

Determinate tomatoes are bushy in habit and fruit on the bush so we don’t remove sideshoots as that removes sections that will crop, but some like to pinch out the growing point to help ripening at that stage or to encourage more sideshoots early on.

When you start growing your own, in the early days you just want to get the plants to stay alive long enough to supply a crop but then these techniques become invaluable in maximising your harvest. It seems like a lot to remember, but , it becomes as automatic as remembering to water or weed.

Fiann’s tips for the weekend

  • Don’t be fooled that the summer is too late for productive gardening, not every seed packet becomes obsolete after March. Keep successional sowing and think of new crops to start.
  • Good to go are: lettuces, Brussels sprouts, savoys and winter cabbages, carrots, courgettes, cucumbers, pumpkins, swedes, parsnips and turnips, sweet corn, salad onions, chicory, beetroot, self-blanching celery and radishes.
  • If you are planting sweetcorn then do it in in blocks not rows. It needs wind pollination and grouping works best. Keep earthing up your potatoes.
  • Plant hanging baskets; keep them indoors until all potential frost risk has passed. Try an edible one — herbs, trailing tomatoes, or strawberries.
  • Outdoor containers can be planted up with herbs — culinary and medicinal.


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