In the excitement of purchasing your first greenhouse, be it of glass or plastic, dreams tend to overtake practicality where a ‘floor’ plan is concerned.
A greenhouse built to hold 10 tomatoes can suddenly, in your imagination, extend to accommodating 20 (plus five capsicums and half a dozen aubergine, as well as chillies). But if you want to make the best use of space while maximising plant health, planning – not cramming – is what’s required when you’re growing under cover.
Begin with the essentials and plan a path so you are not compacting soil in the grow zones. A path needs to be wide enough for you to kneel down on it comfortably as you weed and plant, and long enough to allow you to reach plants growing against the back wall of the greenhouse. What you build it of is up to you. Laying down wooden planks is adequate but tends to provide hiding places for slugs and snails. Gravel, even with weed matting laid under it, will quickly gather soil and sprout weeds. Straw over soil works well as does sawdust but, even better, is a path of flat rocks or pavers that draw in the heat during the day and radiate it out again in the evening, helping to boost night-time temperatures. To prevent soil spilling onto your path, provide an edging of untreated wood attached to pegs hammered into the ground.
Water is an essential in the greenhouse and even if you are on a town supply with access to water on-tap, there will always be times when restrictions apply. Work around this by erecting a spouting along the side of your greenhouse (where design makes this a possibility), and installing a barrel or tank at the door-end of the house to catch rainwater. Note: for safety around small children, always keep rain barrels covered securely.
How you set out your greenhouse floor plan depends on how you will use the structure at various times of the year. If indoor winter gardening is on your agenda, a potting bench along one side of the greenhouse will be the order of the day. Whether you install a purchased structure or build your own, ensure it is anchored firmly in the ground to prevent it tipping and breaking valuable glass panes or tearing precious plastic, and always bear in mind that once water is added to growing mediums, pots become heavy, so your bench must be strong enough to support the load you plan for it.
For those in colder climes who rely on their greenhouse as a ‘frost-free zone’ in winter for potted citrus and ornamentals, such as pelargoniums, staged shelving along the shortest wall of the greenhouse will come in handy. Staged shelving provides multitiered storage with each shelf protruding out further than the one above it so all plants get their fair share of light.
Staged shelving can also be used to hold trays of seedlings. By the time the space is required for this purpose, it is usually possible to move frosttender plants outside to sheltered spots. If cold conditions continue into mid-late spring, frosttender plants can be moved onto the floor of the greenhouse. Once seedlings have been moved into the main garden, pots of heat-loving herbs such as basils and lemongrass, and companion plants such as marigolds, can be grown in pots and take their place on the staged shelving.
By keeping one complete side of the greenhouse clear of structures during winter and early spring, you’ll be able to grow winter greens, such as cool-season lettuce, silver beet, spring onions and Asian greens. As these are harvested, tomato, cucumber, capsicum and other heat loving annual vegetables can take their place.
A place for everything
The main planting season requires the greatest deal of planning where layout is concerned, and thinking about height should be your starting point. Cucumbers and tomatoes will likely be your tallest plants and should be grown in a spot where they can attain the greatest height possible within the confines of the greenhouse. With the traditional pitched-roof greenhouses as well as tunnel houses, this will be along the edge of the central pathway. Shorter plants such as aubergines, capsicums and chillies can be fitted in behind these.
While tomatoes and cucumbers, which require plenty of space, are still young, consider getting the likes of courgettes and pumpkins off to a flying start by planting them in black polythene bags and placing them between these vegetables. Once soil temperatures have warmed up in the outside world, and tomato and cucumber vines require more space, move the courgette and pumpkin plants outside. Carefully split the sides of their polythene containers with a knife and transplant the plants into the main garden. In the same way, potatoes can be planted in bags in the greenhouse to give them an early start and later be moved outside (although they should remain in the bags rather than be transplanted).
Up and at ’em
It’s always a challenge to see just how much you can fit into a greenhouse without compromising the health of your plants. In this regard, smart gardeners will want to maximise growing opportunities by using hanging gardens. These can be purchased baskets with coir linings or plastic buckets filled with potting mix. Remember that it is possible to plant through the sides of mesh baskets as well as in the top of the container. Hanging vertical grow bags are another way of maximising space but as they are a solid structure, they should be hung from frames running in a north-south direction in the central part of the greenhouse to minimise shading. They should not be hung from walls where they will shut out light.
Pollination is always a challenge in greenhouses, especially with the decline of honeybees. Draw these helpful insects into the greenhouse by growing, close to the door, the kinds of plants that will attract them. By growing these in pots, it is possible to replace the flowering plants as they die off with others coming on stream. Attract bees early in the season with flowering bulbs, and over summer with annuals or flowering herbs such as rosemary and lavender. Restrict plantings to low-growing flowers that will not shade the glasshouse (sunflowers, while highly attractive to bees, for example, are too tall).
Enjoy drawing up your greenhouse layout now, as spring starts to make its presence known. The result will be healthier plants and ease of movement as you work in your under-cover garden.