Summer in the polytunnel is like visiting a hotter climate. In the mornings you can smell the richness of the tunnel soil, until it is drowned out by the sweet tang of herbs or the velvet musk of ripening tomatoes. Every plant is bursting with vitality and raring to go so the gardener is much in demand as there always seems to be something to do, from tying up the latest six inches of melon vine to nipping out unwanted side growth from cordon tomatoes. Insect pests grow faster in the warmth too, and a wary eye is needed to stop minor incursions turning into a full-scale war.
Just as summer turns, it is time to plant crops that will be harvested at the end of the growing season. These are plants that are stopped by frost but will crop for longer in the protected microclimate of the tunnel, and include french beans, bulb fennel (sown earlier in modules as they don’t transplant well), French beans, calabrese, Chinese cabbage and pak choi. Sow early short varieties of sweetcorn again for a late crop. Continue successional sowings of salad leaves.
In late summer (and early autumn in warm areas) it is also time to plant your winter crops, since they still have to do much of their growing while light levels are high enough. Making room for them can be problematic since high summer crops are still in full swing, but it is vital to get things started if you want to harvest from your tunnel in the dead of winter. A degree of ruthlessness is necessary in that you may have to lift plants that are still cropping well, but it is possible to undersow some crops if you remove their lower leaves, and module and container growing will allow you to get your winter crops started without disturbing summer planting too early. If needed, consider taking mature salad crops out early and do without them for a short while. After all, there will be more along in a couple of weeks; see ‘polytunnels in autumn’ (coming soon) for a list of potential winter crops.
If the tunnel needs to be re-covered, this is the time of year to do it. In full sun polytunnels can get very warm indeed. This is not a problem provided your crops are kept well watered, but if irrigation is neglected or inadequate plants will suffer almost immediately, and some of them will not forgive you for it. Keep the doors open from early morning until sunset; resist the temptation to leave them open at night because some plants, such as tomatoes, are sensitive to wide variations in temperature. Plant up hanging baskets.
Give extra water to fast-growing plants like tomatoes and the squash family, and mulch around them with comfrey leaves just as they start to fruit – this is more environmentally friendly than proprietary liquid feeds, and also helps to retain moisture in the soil. Every other day, check these fast-growing plants are securely tied up and remove all unwanted side shoots. Tap or mist tomato plants daily for better pollination, and to attract beneficial and pollinating insects into the tunnel make sure that you have a variety of flowering plants throughout the summer – most importantly umbrellifers such as coriander and dill. Why not leave a few plants to finish flowering and save the seeds?
Elephant garlic, courgettes, cucumbers, sweet and chilli peppers (taken green), aubergines, melons, tomatoes, basil, sweetcorn, watermelon, primocaine raspberries and exotics (see p.109). Don’t let early sowings of salad get away from you – keep on top of eating the young plants and be ruthless with composting anything that gets past its best.