As the weather gets warmer in spring, rising greenhouse temperatures are controlled by opening ventilators and doors. The air can get very dry, and this is a problem for plants which prefer it moist, such as cucumbers, foliage plants and many orchids. Damping-down helps. You sprinkle the ground (and staging if any) with water using a hose or watering-can. The evaporation of the water humidifies and cools the air, reducing water stress on the plant leaves. The humidity also prevents tomato pollen from drying out and encourages a better set of fruit. In warm weather the water will quickly dry off and you may need to damp down more than once a day. Capillary matting or old carpet holds more water than a concrete path and they keep the humidity up for longer. In really hot weather you may need to spray the plant leaves as well. Damping down discourages some pests like red spider and thrips which don’t like the humidity. On the other hand, the same humidity can encourage the botrytis fungus that causes grey mould, so carefully remove all rubbish and dead leaves, and don’t damp down late in the day to let the greenhouse dry out before dark.
We have a star in our midst! The new Star Greenhouse from Janssens is now on display. This beautiful little Greenhouse being a Janssens is a substantial one, made with the same aluminium profiles as the Helios range of Greenhouses. It is 1.62m x 2.36m and 1.81m high at the sides. It is available in an attractive black or green powder coated frame with decorative ridge finials and crestings. The glass is 4mm toughened. The price is currently 2,144 euro for the DIY kit (for self assembly). Customers are most welcome to come and view six days a week (Monday to Saturday) during office hours.
As the days get shorter and cooler, greenhouse plants need less and less water. If you go on giving them as much water as in summertime, problems will build up.
Firstly, the plants may continue to grow soft young shoots that will be susceptible to frosts and disease, instead of slowing down their growth-rate and hardening up their stems for the winter.
Secondly, the dampness caused by all the watering will encourage the fungus growth that causes leaf moulds and root rots. This is made worse by the lack of sun to dry off plant and soil surfaces quickly after watering.
Thirdly, the excess water unused by the roots as it drains down through the soil dissolves essential plant nutrients out of the soil and carries them down beyond the roots’ reach. This process is called leaching (sometimes misspelled ‘leeching’, which is an entirely different thing).
What can you do? If you are using a watering computer set it to water less often, for example every fifth day instead of every third. The soil surface can dry off longer between waterings. You could also set it to run for a shorter time. Water in the early morning, so that leaves and soil can dry off before night, when humidity rises as the temperature falls. Instead of spraying with a hose use a can to apply water to the bases of plants without splashing their leaves and wetting the soil between them. Ventilate the greenhouse as often as you can.
Check pot plants by touching the compost surface with a dry finger: if it is damp enough it will feel cool and compost particles will stick to your fingertip. Give little or no water until next time.
We are delighted to announce we have moved into our new state of the art office. The office is a converted stone barn that has been radically renovated to include geothermal under floor heating, insulation to virtually passive standards, heat recovery and a lovely open bright feel to it. We will have an official opening in the spring. At the moment we are in the process of settling in but of course are open for Glasshouses and Polytunnel sales, visitors are most welcome. In due course we will have a showroom in the office for Greenhouse Accessories to complement our display area which has currently 24 structures (Greenhouses and Polytunnels) on show.
De-leafing is one of the tasks that beginners to tomato-growing have to learn. It’s a simple task, and knowing why you need to do it makes it easier still. Basically, you take the lowest leaves off single-stemmed vine tomato plants as they grow upwards. It’s harder and less profitable to do it on bush-type plants with their smaller leaves and tangled growth habit, so just cut out any dead or diseased bits and otherwise leave them alone.
Only the leaves on the top 75 centimetres of vine tomatoes contribute to their growth and yield: the rest are passengers using up feed and water. The lowest leaves are the oldest, most tired and shaded ones that contribute nothing. They are magnets for fungus diseases such as Botrytis (grey mould), and increase the risk of infection of ripening tomatoes by trapping damp stagnant air around them. They can hide weeds and slugs that make things worse again.
There are two ways of de-leafing. In the morning, when plants are still pumped up with water drawn up during the night, the leaf stem will snap off cleanly if bent sharply upwards at the base. The neat wound left behind will be dry and resistant to fungal infection by nightfall. The easiest way to break off leaves is to place your fingers behind the main stem opposite the leaf, and your thumb on the leaf stem about two centimetres above the base, then pull in your thumb smartly towards the main stem to break it inwards. If it hangs on to the stem by a bit at the top snap it downwards to finish the job. Cutting works too, but the stubs that you leave behind can rot and infect the main stem. Compost the leaves, and wash your hands thoroughly.
In hot sunny weather opening all available doors and vents may not be enough to cool your greenhouse, especially if there’s no breeze. Plants suffer from stress if the temperature goes above 25-27°C (77-81°F): they wilt if they fail to get water from the soil and up to their leaves as fast as it evaporates out. If they wilt badly enough the leaf edges will die and turn brown (scorch) and growth and yield will be reduced.
Apart from plenty of watering and full ventilation, shading is the answer. It blocks the entry of infra-red light into a greenhouse and reduces the build-up of heat but it also reduces the visible light needed for plant growth, so use only as much shading as the plants need and only when they need it. A recording thermometer can help you decide how much and when.
Shading paint can be applied to glasshouses with aluminium or painted wood frames, but it can stain polythene, polycarbonate and unpainted wood permanently. Paint it on in spring or summer when needed and clean it off in autumn when no longer wanted. It’s inflexible when the weather changes often.
Shade netting or roller blinds can be fixed up to the inside of the frame or over the top of the greenhouse, and small plants can be shaded with larger plants or sheets of newspaper or tinfoil above them. Shading fixed inside the greenhouse is easier to adjust and blocks direct sunlight from the plants, but it still allows heat to build up. External shading controls the heat better, but can be more expensive to fit and interfere with vents. Automated blinds are handy but cost more.
We are looking forward to participating at the Bloom Show in the Pheonix Park in Dublin next week. It is on from Thursday 29th to June 2nd inclusive. Bloom is a great day out for all the family. Our stand is number 35 and we will have the lovely Helios Victorian 34 that we had on display at Garden Show Ireland recently.
We will be exhibiting at the Garden Ireland Show at Antrim Castle from Friday to Sunday this week (9th to the 11th of May). On display will be a black Helios Victorian Greenhouse. The radio station U105FM will be broadcasting again from our Greenhouse on Friday and Jonathan Pyle (a Director of Polydome) might be interviewed. Last year the show was at Hillsborough in beautiful surroundings and I am told that the Gardens at Antrim Castle are fabulous too. Looking forward to a great show and hoping the weather will be kind.
It’s handy to be able to keep tender plants and grow salad crops in the greenhouse over the winter. Protected from the worst of the frost, they survive the cold so much better than outside. But aphids overwinter better in a greenhouse too. Commonly called greenfly, the many different species come in all colours and some, like woolly apple aphid and lettuce root aphid, are covered in white waxy ‘wool’ to deter predators.
Aphids are weak fliers, and easily killed by cold or washed away by rain. Their only hope of survival outdoors is to lay eggs to hatch out in spring, but in a warmer, drier and wind-free greenhouse the adults can live all winter. When the sap starts to rise in your precious plants they give birth to live young which are bearing young themselves in a few days, so their numbers snowball quickly.
What can you do? Various aphid predators can be bought for releasing into a greenhouse, but most take time to build up and reduce aphid numbers to an acceptable level. For best results use them exactly as recommended. You could rescue adult ladybirds from winter prunings and cleanups, and leave them on the plants in your greenhouse. Sprays come and go: check with your local garden shop or centre to see what’s currently available, and follow the instructions carefully. Some spray very dilute washing-up liquid weekly.
If you want organic remedies try Pyrethrum or sprays based on fatty acids, or on plant or fish oils such as rapeseed oil. Hose down plants with water to dislodge aphids, or squish them on the shoot tips between finger and thumb, or brush them off with a soft brush. Grow root aphid-resistant lettuce varieties. Tagetes grown between other plants can deter aphids.
You could pull out the last of your summer crops from your greenhouse, clean it up for the winter and close it until spring. But why not have it produce fresh green salads for you all winter? If you didn’t sow any leaf greens in recent weeks you can still sow turnip seed in early November and expect the soil to be still warm enough for some growth. It will grow slower than would September-sown crops but still be worthwhile.
Failing that, you can plant roots of turnip and beetroot in pots or the greenhouse soil and let them sprout leaves as if it were next spring. The leaves might not be as good eating as the seedling ones but will be better than nothing. The roots may need some frost to trigger this re-growth. Watch out for slugs.
Chicory has traditionally been grown for forcing in winter. Dig up straight roots about 2cm thick, cut the leaves back to about 2cm high and shorten the roots to about 15cm. Store them flat in sand in a cool shed. Every few weeks, plant a half-dozen or so roots upright and tight together in a medium pot of damp compost, placing it in a shady part of the glasshouse and covering over the top with an upturned pot (cover the drainage holes) to exclude light. Darkness makes the emerging leaves paler and less bitter. Cut them for eating when about 15cm high.
Rhubarb roots can be forced too. Dig up crowns and leave them exposed to frost. Then pack them tightly into a container with old compost, leaving them upright. Put it in a shady part of the greenhouse covered with black plastic. Harvest the sticks when still small and dump the exhausted roots afterwards.