Growing in Module Trays

If you’re growing vegetables in any quantity it pays to be well organized, both on and off the veg plot. Maintaining records of what is sown, where and when is a must and will help you to get the most from your patch but organizing the raising of seedlings is vital too.

For me, module trays – those seed trays divided up into rows of individual cells – are a real godsend. Module trays are what plug plants are grown in and allow the ultimate in regimented planning. Alongside meticulous record keeping they’re what keep my vegetable plot shipshape and regular. If you’re unfamiliar with module trays or have never used them I’m hoping this piece might encourage you to start. Far from being an unnecessary middle step between sowing and planting out, module trays save time and, crucially, will allow maximum use of the land you have available.

Succession Sowing - One Out, One In

Of course, sowing into modules doesn’t suit all crops and in many cases would be impractical (the likes of long-rooted carrots or breakneck-speed radishes for example). But for leafy salads, legumes, veg following on from early or overwintered crops such as members of the cabbage family, and just about any vegetable that needs a reasonable amount of measured space between plants, they prove very handy indeed. You can be starting off one crop in the greenhouse or cold frame while another is still in the ground. That way when the first crop is harvested it’s a simple matter of grubbing out the old to drop in young plants of the replacement crop. No waiting – just out with the old and straight back in with the new.

Another advantage of cell growing is the absolute management of this nursery environment. Module trays raised up onto benching are less likely to be subjected to subversive slugs, pesky pigeons and malevolent mice! They can be given just the right amount of water, a perfectly tailored germination temperature (assuming suitable propagators) and a fulsome root environment designed to speed things healthily along.

Cell Sizes in Module Trays

Module trays are commonly available at standard and half-sized seed tray sizes, as well as narrower strips designed to fit a windowsill. The size of the cells within the trays varies, with those of around 2.5cm (1in) and 5cm (2in) wide most useful to the vegetable grower. Those with a 2.5cm (1in) cell size are ideal for salads and starting off most of the cabbage family. Larger cell sizes are just the ticket for sowing larger seeds (for example squash or beans) and those crops that can be multi-sown, where a small cluster of seeds is sown into each cell.

Seeds can be started off in a seed tray of seed compost before pricking out (transferring) into individual cells. Suitable veggies for this treatment include lettuces, annual herbs and tomatoes. Others can be sown directly into the modules, either one seed per cell for bomb-proof germinators (the likes of corn, squash and zucchini) or three or four seeds per cell for planting out as a cluster – for example, beet, scallions and peas.

In all cases it’s important to fill your trays properly by using quality compost pressed firmly into each cell. Don’t fret about over firming the compost as seedlings prefer a supportive root zone; a well-filled cell will hold more moisture and nutrients, allowing seedlings to remain happy in the cell for longer. To sow, simply make an indentation into the top of the cell and place your seed/s into it. Cover with fresh compost. Larger seeds may need poking down into the compost. Watering the compost thoroughly before sowing will avoid disturbing the seeds. Move the tray to a warm, bright place to commence germination.

Planting Out Module-Raised Seedlings

Planting out cell-raised seedlings is a remarkably satisfying – and surprisingly speedy – process. I’ve been known to go from blank canvass to super-charged salad bed in just half an hour! Before planting your plug young plants they will need to be hardened off to outdoor conditions, if they’re not already accustomed to them. Place the trays somewhere out of harm’s way and cover them with garden fleece at night when cold conditions are forecast. After a week like this they can be set out. For more advice see our article on Hardening Off

Use a dibber (essentially a thick, pointed stick) to make holes for your plugs then water into the holes one or more times until the water is slow to drain out. In this way you will know the ground is properly moistened for the young plants. Poke out each plug by its drainage hole using the blunt end of a pencil and pop the root ball into its hole, firming back the soil around it. Watering before planting saves a lot of effort, as the roots should have enough moisture in their immediate surrounds to break out and settle down with minimal intervention from you. That said, be on hand to water as necessary; think the opposite of little often – big, hearty thirst-quenching soaks once a week at most.

Cleanliness

It is worth buying or acquiring the sturdiest module trays you can afford as they’ll last for many seasons. This throws up its own challenges, however. It is essential that trays are thoroughly cleaned after each use to reduce the risk of fungal diseases lurking about for the next crop. Slugs and snails can also test patience as they find their way into every nook and crevice of stacked trays. Remain eagle-eyed and ready to hoik them out!

Look out for nurseries, gardening stores or fellow gardening enthusiasts off-loading unwanted trays. These can be picked up for a fraction of the cost of buying new. Re-use and recycling websites are another good source. With a modest stack of module trays you’ll be ready to transform the organization of your plot.

For more information see our articles on Raising Plug Plants and Comparing Different Types of Plant Pots.

By Benedict Vanheems.