"Remember - always sow the seeds. You can catch up on everything else - but if you get behind on doing that, then there's nothing you can do about it." .......... (A great piece of advice I was given many years ago)
Sow in gentle warmth in pots or modules for late summer tunnel/greenhouse cropping:
There's still time to sow French beans (dwarf and climbing), edamame (soy) beans, sweet corn, courgettes, pumpkins, summer squashes, marrows and melons. You can also still sow cucumbers & gherkins (Restina excellent variety) for late summer and early autumn cropping, also calabrese/Italian broccoli (Green Magic good) and self-blanching celery for later autumn crops.
Shade propagators and young seedlings well from strong sun at all times now using and make sure to turn off propagators during the day, if it's warm enough. The temperature can rise dramatically in greenhouses and tunnels at this time of year, and if it's too hot - things can quite literally cook! Although in theory you can sow everything outside now - the nights can still be quite cold, so it's still worth sowing tender crops like French and runner beans, sweetcorn, basil, cucumbers, melons, pumpkins and squashes in pots or modules in a greenhouse, tunnel or propagator for planting outside in a couple of weeks. These need reliable warmth and will germinate far more quickly undercover - often in 2-3 days - making them at least a week to to 10 days earlier than anything you might sow now outside. In addition, if the weather turns very wet - seeds can rot. Sowing in modules also avoids potential losses through slug damage, leather jackets and other pests - and it helps you to make better use of valuable growing space.
Sow some quick growing annuals now directly into the tunnel soil in odd corners to attract bees, hoverflies and other beneficial insects, these provide them with vital pollen and nectar.
It's also it's time to start to thinking about the slower developing winter tunnel crops. Self-blanching celery for winter tunnel cropping needs to be sown in cool conditions around mid - late June, for tunnel planting later, as it is quite a slow developer at first.
Outdoors, sow in modules, in a seedbed for transplanting, or in situ where they are to crop:
Amaranth (callaloo), beetroot, carrots, cabbages (leafy non-hearting and late stone head types), peas (early vars. such as Kelvedon Wonder from now to ensure cropping before early autumn frosts), calabrese and 'tenderstem' broccoli, courgettes & marrows, 'Witloof' chicory (for winter forcing), endives, salad onions, Florence fennel, French and runner beans, leeks (an early var. for baby leeks), land cress, lettuces, perilla, orach, kohl rabi, kales (early June for winter cropping), radishes, rocket, Swiss chards, spinach, summer squashes, sweet corn, white turnips and swedes, summer purslane, lamb's lettuce, salad mixes, soft herbs such as basil, oregano, parsley, coriander, dill, fennel etc. and perennial hardy herbs including sorrel.
Also sow some single, fast growing, annual flowers such as limnanthes (poached egg flower), calendula, Californian poppies, convulvulus tricolour, nasturtiums, phacelia, sunflowers etc. to attract beneficial insects like hoverflies to help with pest control, and bees to help with crop pollination.
Sow fast-growing green manures like buckwheat, red clover, mustard (a brassica so watch rotations) and phacelia, to improve the soil, 'lock-up' carbon and feed worms (after digging in), on any empty patches of ground that won't be used for 6 weeks or more, or which needs improving. Red clover, buckwheat and phacelia in particular are also great for bees! (You can 'bulk buy' buckwheat seed very cheaply from your local health food shop - just don't get 'roasted' buckwheat - it obviously won't germinate!!)
In warm well drained soils outside, tubers of oca, mashua, sweet potatoes and yacon can be planted now
(although all of these will produce a better crop in the tunnel, particularly in Ireland, as they like warm soil, bulk up late and are vulnerable to autumn frosts. They also prefer well drained conditions) With yacon - you plant the small baby 'growing' tubers that cluster round the stem area at the top of the larger tubers. These all need a long growing season as they only begin forming their tubers in late autumn - in colder frost prone areas growing them in a greenhouse or tunnel is the best way to get a reliable crop, but be aware that Yacon in particular needs a lot of space!
*Sorry to mention it at midsummer - but it's now time to think ahead to what crops you will want to grow over the winter, in the polytunnel or outside, and buy the seeds now if you haven't done already! Otherwise they may disappear off the shelves, when garden centres re-organise their stock for the autumn season which they tend to do around the end of June. Online seed companies may also be sold out of popular varieties by then.
(Please note. I really enjoy sharing my original ideas and 40 years experience of growing and cooking my own organic food with you. It's most satisfying and naturally also very complimentary if others find "inspiration" in my work......But if you do happen to copy any of my material, or repeat it in any way online - I would appreciate it very much if you would please mention that it originally came from me. It's the result of many years of hard work and hard-won experience. Thank you.)