Suc­cess with green­house grow­ing

Alan Titch­marsh shares his ad­vice for get­ting the most out of your green­house, so you can en­joy grow­ing all year-round, what­ever the weather

Gardeners' World - - Contents -

Alan shares tips on get­ting the most from the gar­dener’s glassy sanc­tu­ary

A green­house is some­thing of a sanc­tu­ary for the gar­dener – a place to be en­joyed in all weathers

To call a green­house ‘ the cathe­dral of the gar­den’ might be stretch­ing things a bit. After all, a 6ft by 8ft glass box is a far cry from West­min­ster Abbey. But there is some­thing about even the small­est of green­houses that of­fers a kind of hal­lowed at­mos­phere. It be­comes not sim­ply a place to grow plants that would other­wise fail to thrive out in the open, but also some­thing of a sanc­tu­ary for the gar­dener – a space to be en­joyed in all weathers, and an op­por­tu­nity to grow toma­toes, pep­pers cu­cum­bers and aubergines, as well as ex­otic or­na­men­tal plants, and you don’t need to run up a heat­ing bill that would make a Rus­sian oli­garch blench. If you long for toma­toes weeks be­fore they are ready in the gar­den, or if you want to over­win­ter ten­der pelargo­ni­ums and other bright-flow­ered plants; if you fancy col lect­ing cacti, suc­cu­lents, strep­to­car­pus or ten­der fuch­sias; if you yearn for cu­cum­bers and mel­ons at your bid­ding, or a grapevine yield­ing suc­cu­lent fruits, then a green­house is a must. In colder parts of the coun­try, a green­house is even more valu­able than in the milder south, as it will ex­tend your grow­ing sea­son. It will al­low you to start plants – such as dahlias, ten­der veg­etable seedlings and bed­ding plugs – into growth ear­lier than they could be risked out­doors. It will also pro­long the grow­ing sea­son when the nights turn chilly. A green­house also en­ables you to grow a host of ex­otic plants that might other­wise be off lim­its, for ex­am­ple, cit­rus fruits and ba­nana plant s can be over­win­tered un­der cover and put out in sum­mer. Un­der the cov­er­ing of glass – even if it is kept just frost free – a part of your gar­den is opened up for year-round use and en­ter­tain­ment.

Set­ting the stage

If you want to grow let­tuces and toma­toes in a soil bor­der, leave one side of the green­house with its earth ex­posed. Al­ter­na­tively, stag­ing can be run all round the green­house. It is cer­tainly worth in­vest­ing in sturdy stag­ing (waisthigh shelv­ing) down one side of the green­house so that pot plants can be eas­ily tended to. If you are plan­ning to dis­play the likes of pelargo­ni­ums, fuch­sias, schizan­thus and strep­to­car­pus, then tiered stag­ing will give you a wa­ter­fall ef­fect of fo­liage and flow­ers. If you plan on grow­ing a grapevine, the

The more ven­ti­la­tors a green­house has, the hap­pier the plants

roots can be planted in the soil and the stem led up be­hind the stag­ing, with the vine stems ( rods) slung from the glazing bars above. In my own green­house, I have stag­ing all round so that toma­toes and cu­cum­bers can be grown in large pots or grow­ing bags placed on it. A shelf un­der­neath the stag­ing, where the light lev­els are lower, is a great spot for maid­en­hair ferns, which en­joy shade and hu­mid­ity. Make sure that plants that de­mand plenty of sun­light are put where they will re­ceive it – on shelves near­est the glass.

Ven­ti­la­tion and wa­ter­ing

In your ex­cite­ment about hav­ing some­where warm to work in win­ter, don’t for­get the im­por­tance of ven­ti­la­tion, for in sum­mer the green­house will turn into a fur­nace with­out ad­e­quate air cir­cu­la­tion. The door can be opened, but high-level (ridge) and lower (eaves) ven­ti­la­tors are vi­tal to en­sure that tem­per­a­tures can be kept at an ac­cept­able level and that hu­mid­ity can be con­trolled by a healthy flow of air. The more ven­ti­la­tors a green­house has, the hap­pier the plants – and the gar­dener. If you are out at work all day, au­to­matic ven­ti­lat­ing arms can be fit­ted to open the vents when the tem­per­a­ture rises above a cer­tain point. They are won­der­ful life- savers for plants grown by gar­den­ers who can’t be in at­ten­dance all the time. Shad­ing, too, is vi­tal be­tween May and Septem­ber to pre­vent plants from be­ing scorched by the mag­ni­fied ef­fect of the sun. When it comes to wa­ter­ing, a tap in­stalled in­side the green­house will save you a lot of lug­ging a hosepipe or wa­ter­ing can up and down the gar­den. Au­to­matic wa­ter­ing sys­tems are now avail­able at rea­son­able cost and can be rigged up to a small bat­tery­op­er­ated com­puter fit­ted to the tap. When you are ab­sent for long pe­ri­ods of time they can be a use­ful al­ter­na­tive to try­ing to find a help­ful neigh­bour who knows how and when to wa­ter plants.


Elec­tric­ity is by far the most ef­fi­cient way of heat­ing a green­house, since it of­fers dry, con­trol­lable heat. There are lots of green­house heaters that are fit­ted with ther­mostats to en­sure ef­fi­ciency and econ­omy. But don’t un­der any cir­cum­stances use a do­mes­tic heater in the green­house. It won’t be safe for use where wa­ter is around and in ext reme cir­cum­stances may even prove lethal. Un­less you want to grow trop­i­cal plants in win­ter you won’t need to heat your

green­house to a high tem­per­a­ture. Most plants – such as cit­rus, pelargo­ni­ums and ten­der fuch­sias – will be happy if the tem­per­a­ture doesn’t drop be­low 7°C (45°F), though if you can keep them a lit­tle warmer than this they will con­tinue grow­ing. Free­dom from frost is crit­i­cal – un­heated green­houses are use­ful in spring for the shel­ter they pro­vide but in the dead of win­ter they of­fer lit­tle use­ful pro­tec­tion.

Pest con­trol

While a green­house has many ad­van­tages, it has its own range of pests – red spi­der mite, mealy bug, white­fly, vine wee­vil and scale in­sects. These can be con­trolled with bought preda­tors and, in the con­fines of a green­house, this bi­o­log­i­cal con­trol is usu­ally more ef­fec­tive than it is out­doors. When it comes to dis­eases such as mildew and botry­tis, ad­e­quate air cir­cu­la­tion will

keep such out­breaks to a min­i­mum. Re­mov­ing dead leaves and flow­ers from plants will help and is a rou­tine that ev­ery green­house gar­dener gets into the way of. For me, it’s one of the joys of my morn­ing! Turn over for our green­house buyer’s guide

Septem­ber 2017 gar­den­er­

Green­house con­di­tions are ideal for onion stor­age in win­ter

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