Robert Smith

10 Apr 2024 13:12

The Ultimate Guide to Container Gardening in a Greenhouse


Container gardening in a greenhouse is a fantastic way to extend your growing season and maximise your garden's productivity, regardless of its size. Using pots, troughs, growbags, hanging baskets, and even tin cans allows you to create multiple areas to produce different veggies in a protected environment.  With our changing weather, growing in containers also helps prevent loses should your greenhouse flood or become waterlogged, as containers are easier to move and keep plants roots above the soil level.  So, lets walk through the essentials of successful container gardening, from selecting the perfect substrate to innovative watering and drainage solutions that will keep your plants healthy and happy.

Choosing the Right Substrate

Annual Vegetables: Opt for a nutrient-rich potting mix that includes peat-free compost or coconut coir, and vermiculite or perlite. This blend ensures both moisture retention and proper aeration, key for the growth of annuals.  There are plenty of good composts on the market, from wool based to those using green waste, so it may be best to try a few to see which works for you the best.


Permanently Planted Vegetables: Use a heavier mix, incorporating more loam-based compost and garden soil, to provide long-term support and nutrition.  This type of planting works well for citrus trees, grapes, and any other perennial fruit you may be growing in the greenhouse.  Basically, if your plant is a permeant feature of the greenhouse, you want the substrate its growing in to be as near to growing in the ground as you can, otherwise compost can sink and become depleted of nutrients quickly.


Enhancing Water Management

Drainage: Proper drainage is vital. To improve this, add a layer of crocks (broken pottery) or pebbles at the bottom of your containers. This age-old technique prevents excess water from sitting at the container's base, reducing the risk of root diseases. For pots with built-in drainage holes, this extra layer ensures water flows freely, keeping roots healthy.  If you are growing in metal animal water troughs, be sure to make ample drainage holes in the base.  You may also need to add holes to terracotta pots if they are slow to drain, this can be done easily with special ceramic drills you can buy online.


Water Reservoirs: Some modern containers come equipped with water reservoirs at their base, designed to help manage watering by allowing plants to absorb moisture as needed. This is particularly useful in a greenhouse setting where temperatures can fluctuate.  You can also buy Olha pots; these are large containers which are embedded in the compost with just the neck showing, allowing you to fill them with water which will slowly seep through the porous material and water your plants.


Wool Linings for Hanging Baskets: Lining your hanging baskets with wool can help retain moisture, slowly releasing it back to the plants when they need it most. This method is ideal for water-loving plants like tomatoes and cucumbers, ensuring they stay hydrated without constant attention.  You can also use a layer of wool at the bottom of your pots to slow the water speed of which it drains from the holes, allowing plants longer to hydrate, and save water at the same time.


Water Crystals: Incorporating water crystals into your potting mix can significantly improve water retention. These crystals absorb water and expand, slowly releasing moisture back into the soil as it dries out. They're especially useful for containers that dry out quickly, reducing the need for frequent watering.


Dripper systems:  These include sprinklers, drippers and sprayers which can be added to each container, perfectly directing the water where it needs to go for maximum effectiveness.  These can be connected to a garden tap or water butt, with some even having solar panels so they don’t require mains electricity, perfect if you are on an allotment or site with few amenities.


Feeding: Container-grown plants rely entirely on you for their nutrition. Use a balanced, water-soluble fertiliser every two weeks during the growing season. For permanently planted veggies, consider a slow-release fertiliser that will feed them for up to six months.  You can make your own liquid feed by soaking comfrey leaves which are tied in an old pillowcase in water for a few weeks, then dilute the feed one part to 10 parts water before using on your fruiting plants, this will help ensure a good crop of home-grown, tasty veg.  If this seems like too much work, simply lay the comfrey leaves on the surface of the compost as a mulch, they will quickly rot down and help feed your plants while reducing water evaporation at the same time.

If you prefer not to make your own plant feed, there are plenty on the market to choose from.





Space-Saving Planting Techniques

Hanging Baskets: you can easily grow tomatoes and cucumbers in hanging baskets to save space and produce a crop from an unused space.  Choose hanging basket varieties which are usually smaller fruited, so they don’t rip themselves from the basket with their own weight.  You can get red, yellow and orange tomatoes for baskets, in fact there are even striped tomatoes that will work well.  Some cucumbers are also great in baskets, though they will need to be at least 30cm wide and 20cm deep; remember to use wool or water crystals in baskets, this prevents them drying out too quickly.



Using the space beneath tomato plants by underplanting with basil or marigolds, which can enhance tomato flavour and deter pests.  It is space that would otherwise not be used, so by growing a tasty crop of basil you can harvest your tomatoes at the same time, ideal for an Italian inspired meal.

If you aren’t a fan of basil, why not use small-sized chillies or herbs at the front of containers, adding variety and maximising every inch of your greenhouse space.


Growing in containers in your greenhouse ensures a productive harvest and allows you to grow differing plants with differing needs, all in the same space.  By selecting the right substrates, employing innovative watering solutions, and optimising space with creative planting, your greenhouse can become lush and productive. 


Images courtesy of Robert Smith and Darren Lakin

Om Robert Smith

Rob is a seasoned gardener, specialising in growing edible plants. Not only does he write for multiple national Gardening Magazines, but he also appears now and again on TV and radio, sharing his passion for the “Grow Your Own” lifestyle on social media (@robsallotment).  Alongside his public persona, Rob also works with several of the counties best known gardening companies, including Suttons, Thompson & Morgan, Dobies, and The Organic Gardening Catalogue, to source new and exciting types of fruit, veg and flowers to be launched into garden centres across the UK and Europe.  At home you will find him in his Kitchen Garden, come rain or shine, accompanied by his faithful companions, Nipper and Reggie.

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