Planting a Window Box

Window boxes are especially useful for livening up town and city gardens where outdoor space may be at a premium, but even sprawling rural properties and village high streets can be revitalised with a colourful floral display.    

The wonderful thing about window boxes is their versatility. Even if you live in a unit, with little or no outdoor room, you can still have a garden in a window box. Window box displays can be as temporary or permanent as you like. You can completely revamp them with the seasons or opt for a consistent year round display. If you're less interested in their visual appeal you can use them to grow a kitchen garden, to attract birds and butterflies, or for scented flowers.    

Why Choose a Window Box?

  • You live in a small apartment, with little or no outdoor places to grow plants.
  • They provide decoration - both from the outside looking in, and inside looking out.
  • They can help you feel in touch with nature.
  • They give you something to nurture and look after.
  • Growing plants is soothing for the soul.
  • You can benefit from wonderful fragrances wafting indoors.
  • You can get a great deal of enjoyment and pride from them.
  • They can be used to grow herbs and vegetables.

Practical Pros and Cons
When weighing up whether or not to install window boxes, you may find the following checklist of practical considerations to be useful.
Possible drawbacks:

  • They may block out light from a window, making a room darker inside.
  • If plants are not healthy they can look unsightly from indoors.
  • They can be difficult to water and feed - especially if windows don't open.
  • You may not be able to spray with insecticides from inside.
  • Soiled water may stain window ledges and building facades.
  • Over watering may cause damp problems on unsealed surfaces.  

Possible advantages:

  • Plants are continuously in view from inside so you will quickly notice and attend to problems.
  • If the window opens then plants are easy to tend to.
  • They are relatively simple to install - and uninstall if required.
  • Boxes can be secured with brackets or bars - so they don't fall.
  • There are a range of different possible types to suit a variety or needs and tastes.
  • Boxes are available in different sizes to suit different widths.
  • Wooden boxes can be custom made.

Securing Boxes

Many people shy away from window boxes because they don't realise that there are many ways to install them. You don't even need to have a window ledge to have a window box. In fact, provided it gets a reasonable amount of light, you can even place a window box on a window sill inside.  

The simplest approach is to install a metal restraining bar across the span of the window.  The bar is lined up several inches higher than window ledge and affixed to the outside walls on each side of the window frame. A series of pots and saucers can be placed on the window ledge within the restraining bar which prevents them from toppling off the ledge. Aside from individual pots, restraining bars can also be used to secure a variety of window boxes.

Another option is to first screw metal U-shaped brackets onto the window ledge and to sit the box inside them. The brackets can be painted beforehand in the same colour as the box so that they blend in. If the boxes need to be placed below the window ledge then L-shaped brackets can be screwed to the wall to house them. On balconies and in courtyards, window boxes can also be positioned along the tops of walls or suspended on brackets on the inside or railings.

For heavier types of window boxes such as those made from stone or precast concrete the sheer weight of the box and its contents is often enough to guarantee it won't move. However, if they overhang the window ledge they'll need to be restrained.  Some window boxes can be screwed directly onto window ledges.

Installation Tips

  • Pre-paint brackets or bars before fixing into place.
  • Use two brackets per window box, or one restraining bar per window frame.
  • Measure carefully and mark the positions - line up brackets the same distance from each end of each window box.
  • Step back and make a visual check before drilling - use a spirit level if feasible.   
  • When drilling into masonry and brickwork always choose a masonry drill bit - it won't shatter or instantly blunt.
  • Wear protective eye goggles and ear muffs.
  • Put raw plugs into the holes before screwing down brackets or bars.
  • Stainless steel, solid brass and aluminium screws resist rust the longest outdoors.

Window Box Options

There are several window box systems from which to choose. Individual plant pots may be used to mimic a window box. These may be placed inside a window box sleeve or a box itself so that they are not visible. If you want the individual outlines of the pots to be appreciated then select interesting pots. If you don't wish to use a window box or sleeve and only have fairly ordinary pots you can disguise them by growing trailing and spreading plants. Just be sure to install a restraining bar so the weight of plants does not cause them to fall.  

Wooden window boxes can look very attractive, especially when painted. Painted wooden boxes also last longer than waxed, stained, varnished or untreated timber. If you can't find wooden boxes which blend with the exterior colour scheme of your unit or house, consider painting them yourself with a good quality exterior paint. Look for wooden boxes that have been made from durable materials such as marine ply. If the inside has been painted with pitch they will also last longer. If not, use a lining material such as PVC before planting.

Wooden window boxes are also sometimes available which comprise of a wooden outer sleeve with an inner plastic box. Although not as sturdy as solid wooden boxes, these have the advantage that the interior plastic box can be easily lifted out for replanting. This means that you don't have to be especially strong to maintain them. Also, the inner plastic box can be replaced if it splits - which plastic tends to do over time. From the outside, they can look just as attractive as solid wooden boxes, and they are cheaper.  

Concrete and reconstituted stone window boxes are the most durable. The main disadvantage is their weight. If they have to be installed from the outside then they can be difficult to get into position - particularly from ladders. Once in place, they may be even more difficult to remove. That said, they will last indefinitely, and the exterior can be painted to revamp them when needed or to match the changing painting schemes of the building.  Terracotta boxes can be similarly heavy but not as long-lasing since they can crack in frosts and flake in heat. Also, you shouldn't paint them.

Fibreglass is another good choice. Boxes made from fibreglass can be moulded and coloured to mimic other materials such as stone or lead. Decorative faux lead boxes look great on older style inner city properties. They can eventually become quite brittle but will easily outlast most plastics.

Plastic and PVC boxes are good value, but the least durable option. Some plastic boxes appear quite solid to begin with but bow and sag once filled with soil and plants. Look for those which claim to have more resistance to radiation damage from sunlight. Plastic window boxes and pots can be placed inside more durable and attractive sleeves and boxes from where they can be easily lifted out and replanted.  

Variations on window boxes include plastic lined metal hay racks mounted on the wall below a window, and purpose-made mangers which are similar in appearance but smaller. These can be a good option where the window ledge is too narrow to support a window box.   

What Type of Plants?

Choosing plants for window boxes requires some careful thought. A formal window box will have some structural plants, a symmetrical theme, and most likely some seasonal bedding plants to provide colour. For instance, it may contain a central conical box tree a ball box either side and perhaps sine railing ivy at each corner and down the middle. The remaining spaces may be filled in with the seasons. Box trees are a god option because they can be clipped to provide a tight shape.

For a less formal or cottage garden style, a window box can be planted with a mixture of shrubs and flowers. If you want a productive garden in your window box then herbs are a good choice. Try choosing dwarf cultivars of species like lavender and rosemary, and some naturally lower growing or spreading types like thyme and chamomile. You could intersperse seasonal herbs like basil and chives. Some vegetables are also available in dwarf forms which won't take up too much room. For instance - chilli, lettuce, cabbage, carrots, peas and salad tomatoes.

For a semi-permanent display consider having a few small shrubs which provide the general structure. These can remain in position throughout the year and only the surrounding bedding or seasonal vegetables are changed. For a permanent display or kitchen garden choose plants which will not quickly outgrow the box.  If you are unable to water the plants often try choosing plants which are not terribly thirsty - you could always consider cacti and succulents.

Do's and Don'ts for Choosing Plants

  • Don't choose plants which grow too tall - they'll ultimately block out your light.
  • Try not to select bushy species - they'll end up squashed against your windows.
  • If access is difficult, choose plants with low maintenance requirements.
  • Use trailing plants at the front edges to soften the outline of the box and extend the visual impact.
  • Select taller plants for the rear of an outside display.
  • For a display which looks good from both inside and outside use the same height bedding plants throughout.
  • Avoid plants with invasive roots - they'll take over.
  • Always choose healthy specimens - pests and diseases will spread quickly in a contained environment.

Tips for Planting a Window Box

  • If there are no drainage holes in the box, drill some in it - plants will rot if waterlogged.
  • Place some crocks or stones over the holes to stop the soil from washing away.
  • Plant heavy window boxes in situ - you might not be able to move them easily once planted.
  • You can place the soil directly into some types of boxes including plastic, terracotta, fibreglass, stone, and concrete.
  • Wooden boxes and hay racks need a plastic or metal liner (unless wooden boxes are coated on the inside with pitch or bitumen).
  • You can use a liner in any box to make it easier to lift out the entire display when you want to change it or revamp it.
  • If you place individual pots inside a sleeve or box you can always fill around them with decorative moss - you can also use moss or straw around the outside of liners in mangers.
  • Choose a suitable soil e.g. one formulated for vegetables for a kitchen garden box.
  • Make sure you include wetting agent, particularly if plants are exposed to full sun, and a slow release fertiliser.  

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