Green­house buyer’s guide

A green­house is a big in­vest­ment – fi­nan­cially, and in terms of the time you spend tend­ing it. So it’s im­por­tant to make the right choice. Use our guide to help you weigh up the op­tions

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A com­pre­hen­sive guide to choos­ing a green­house to suit your needs

Where should you put your green­house?

In an ideal world, your green­house would go on a com­pletely level site that re­ceives un­in­ter­rupted light from all di­rec­tions yet is shel­tered from strong winds, and is not too close to any trees that would drop leaves on it. Your green­house would be close to the house, to make it eco­nom­i­cal to run wa­ter and elec­tric­ity to it. It would also have easy ac­cess, in­clud­ing all the way around, for ease of clean­ing. Of course, few of our gar­dens pos­sess such per­fect con­di­tions. But do avoid full shade and ar­eas that are prone to wa­ter­log­ging. If you want to grow plants di­rectly in the ground, then site your green­house away from large es­tab­lished plants that will thrust their roots into it. Slop­ing po­si­tions will need to be lev­elled, so do al­low for this in your bud­get.

What is your bud­get?

Alan says: “Work out your bud­get and buy the best you can af­ford. When it comes to green­houses ‘cheap is dear’, since you will most likely have to re­place an in­ex­pen­sive one more quickly than one that is well made.”

You can spend any­thing from around a cou­ple of hun­dred pounds for a lit­tle lean-to, to sev­eral thou­sands, de­pend­ing on fac­tors like con­struc­tion ma­te­ri­als, size and shape. The cheap­est green­houses are made of alu­minium and sit di­rectly on the soil, with beds for you to grow your plants. Fac­tors that will in­crease the cost in­clude: Con­struc­tion ma­te­ri­als and choice of glaz­ing Size Be­spoke shapes In­stal­la­tion Land­scap­ing work to level the ground In­stalling a solid base In­stalling power and wa­ter Equip­ment in­side the green­house

What type of frame?

Alan says: “Choose a green­house de­sign that will suit your house and your gar­den – mod­ern and sleek, or tra­di­tional with finials.” Alu­minium Alu­minium green­houses are cheap and strong. The glaz­ing bars are thin, so they let the most light in. They re­quire no reg­u­lar main­te­nance. Pow­der-coated alu­minium is more ex­pen­sive but comes in sev­eral colours and looks at­trac­tive. It will last longer than un­treated alu­minium.

Wooden Wooden frames look tra­di­tional. The glaz­ing bars are wider than alu­minium, so less light gets in. But wood re­tains heat bet­ter than alu­minium – ex­tend­ing the grow­ing sea­son at the start and end of the year.

Soft­wood green­houses are cheap but need to be painted/treated reg­u­larly to pre­vent rot­ting. They have a shorter life span than hard­wood, but if pres­sure treated, they can last al­most as long.

Hard­woods, such as Western red cedar, are more ex­pen­sive, but they do not need reg­u­lar main­te­nance and will last much longer.

Alu­minium strips over wooden bars ex­tend the life of the frame.

Frame­less New tech­nolo­gies al­low green­houses to be with­out a frame. Th­ese let in max­i­mum light and are easy to clean. The cost is com­pa­ra­ble to a good-qual­ity wooden green­house. Some gar­den­ers worry that birds would fly into a frame­less green­house.

What is the best glaz­ing?

Glass lets in the most light, but of­fers lit­tle in­su­la­tion dur­ing the win­ter. Tough­ened glass is more ex­pen­sive, but stronger and safer – if it breaks, it shat­ters into small pieces rather than dan­ger­ous shards – and is ideal for door­ways. Poly­car­bon­ate sheet­ing is good for in­su­la­tion dur­ing the win­ter, the dif­fused light is great for plant growth and it doesn’t need shad­ing. How­ever, it doesn’t let in quite as much light as glass, and the thicker the sheet­ing, the less it al­lows in.

What is the best size?

Alan says: “Buy a big­ger green­house than you think you will need; you’ll soon fill it!”

A high roof height will al­low in more light and im­prove air flow, help­ing plants to grow straight and strong. Height is also use­ful for train­ing plants up canes. You won’t have to stoop, of course, but you’ll need long-han­dled win­dow-clean­ing tools. It’s also eas­ier to main­tain even heat with a high roof.

A rec­tan­gu­lar green­house has the tallest sides, and it is easy to make use of the space in­side with stag­ing and shelves.

A lean-to is the an­swer where space is re­ally tight. It is warm, but the light is one-sided.

Domes and oc­tag­o­nal green­houses al­low in lots of light and are bet­ter at with­stand­ing high winds, but the roof is gen­er­ally lower than other shapes.

What sort of vents should you choose?

Good air flow is vi­tal to cool a green­house and re­duce hu­mid­ity, to limit fun­gal dis­eases. To work out how many vents you will need, mea­sure the floor area and make sure the roof vents are equal to 15-20 per cent of this area, and the side vents plus the door are equal to 15-20 per cent again.

Roof vents are the most ef­fec­tive and can be au­to­mated so that they open when the green­house reaches a cer­tain tem­per­a­ture, although they can be slow to re­spond.

Lou­vered side vents are a use­ful ad­di­tion, or sec­ond choice – but them clear of clut­ter.

The door is a good source of ven­ti­la­tion, so

opt for as large an open­ing as pos­si­ble; it also helps with ac­cess when you have lots to carry.

In a large green­house, use fans, hung mid­way be­tween the vents, to im­prove air flow.

Do you want a soil base or a solid base?

Green­houses can be built with a paved or con­crete base, or placed onto com­pacted soil (us­ing a steel frame ce­mented into the ground at the cor­ners) that you can grow di­rectly in to.

Soil base Cheap to con­struct Can grow plants up full-height canes Roots can grow beyond the bound­aries of the green­house Sim­ple wa­ter­ing regime Po­ten­tial build-up of pests and dis­eases Soil struc­ture de­te­ri­o­rates Lim­its an area to one use Not suit­able for very large green­houses

Alan says: “A green­house with glass sides is best if you plan on grow­ing crops in the soil bor­ders – toma­toes, mel­ons, cu­cum­bers, or a grape vine.”

Solid base Durable and solid Easy to keep clean Stag­ing can be moved to pro­vide flex­i­ble height grow­ing spa­ces Stor­age un­der benches is pos­si­ble Free from ver­min and moles Makes it pos­si­ble to have a knee-high brick wall, which helps keep heat at the base and makes the con­struc­tion ex­tra-strong Ex­pen­sive if hard land­scap­ing is needed Can only grow plants in con­tain­ers or raised beds

Do you want stag­ing in your green­house?

Th­ese are wide, waist-high shelves that run around the edge of the green­house. They can be free­stand­ing or built-in. Slat­ted stag­ing is ad­e­quate and the most com­mon. Solid stag­ing, or trays placed on slat­ted stag­ing, al­lows you to use cap­il­lary mat­ting for wa­ter­ing. It’s use­ful to have an area of solid stag­ing for pot­ting up.

What about shad­ing?

The sim­plest form of shad­ing is a kind of white­wash that is sprayed or brushed onto the glass in late spring and washed off in late sum­mer, but it is messy to ap­ply and to re­move. Shade net­ting is clipped onto the bars on the in­side of the green­house. It must be taken down and washed reg­u­larly to re­move any pests or fun­gal spores. The best, but most ex­pen­sive, op­tion is in­te­gral blinds, prefer­ably on the out­side so that they in­ter­cept the sun’s rays be­fore they pen­e­trate the glass. In­ter­nal blinds are a good sec­ond choice.

Are you go­ing to heat it?

Elec­tric­ity is a cost-ef­fec­tive method of heat­ing a green­house, but you will need to get an elec­tri­cian to in­stall elec­tric points for lights, heaters and prop­a­ga­tors at the out­set. Propane heaters are a good idea where there is no elec­tric­ity sup­ply. Record max-min ther­mome­ter read­ings to mon­i­tor heat­ing ef­fi­ciency in the green­house. In­su­lat­ing the green­house with bub­ble wrap or dou­ble glaz­ing will keep down the bills, but make sure the vents can open. Heat mats and prop­a­ga­tors are a cheap way to keep a small range of plants pro­tected dur­ing the win­ter months. Wa­ter stor­age tanks pro­vide warm wa­ter and ab­sorb the day’s heat and can help to keep the green­house frost-free overnight.

Septem­ber 2017

Oc­tag­o­nal de­signs are good at with­stand­ing high winds Lou­vered side vents are less heavy to oper­ate than sin­gle pane vents Roof vents are es­sen­tial to re­duce hu­mid­ity in a green­house Septem­ber 2017

Solid stag­ing pro­vides a handy area for pot­ting up Shade blinds dif­fuse the sun’s scorch­ing ef­fect Septem­ber 2017

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