Planting your container
The success of your container display relies on the preparation you put in before you add the plants. The key is to create an environment where the plant will have access to water and nutrients, won’t get too hot or cold, won’t be waterlogged and will have a stable medium for its roots to grow into. It’s also important to prepare the plants themselves, so the shock of moving from one environment to another isn’t too great.
Filling your container
There are five main considerations when filling your container prior to planting:
Drainage
Most containers will come with drainage holes at the base. If you are permanently planting the container, ensure that the container has holes in the base and that you place something over the holes to ensure they aren’t blocked by soil. There are plenty of different things you can use for this, eg crocks (bits of broken clay pots), polystyrene, stones or corks. The larger the pot the deeper your drainage layer should be, as more water will collect in the growing media and need a way out.
For short term plantings (eg annuals) it’s generally not necessary to place anything over the holes as the plant won’t be in the pot long enough for waterlogging to occur. You can even get away with containers with no holes for short term planting, just make sure they don’t get waterlogged (put them in a sheltered spot where rainfall won’t reach them or move them under cover if you have a lot of rain). If you’re not prepared to take this extra care, holes can be made at the base of most containers. Don’t forget that hanging baskets which are lined with plastic could also do with a couple of drainage holes if they’re going to be rained on a lot!
Water retention
Depending on your choice of container you may need to take extra steps to help it retain water. Terracotta pots, for example, are porous and absorb the water out of the growing media. To get around this you can line the container sides with plastic (eg old carrier bags) to prevent moisture leaving through the sides. Water-retaining granules can also be added to the soil – make sure you use no more than the quantity recommended by the manufacturer as the granules swell significantly and can push your plants out of the pot! An alternative to granules is to take a sponge, chop it into small pieces in a food processor, and add that into the compost mix. For small containers and baskets, place a small pot (such as the polystyrene ones from takeaways) in the base of the container so it can collect water and become a reservoir, or simply place a sponge in the base.
Pots and troughs with water reservoirs built in are also available, which might be particularly helpful for pots in hard to reach places, so long as the additional weight of the retained water isn’t an issue.
Insulation
Some containers, particularly metal ones, offer very little insulation and will heat up and cool down rapidly, leaving your plants’ roots vulnerable to the extremes of temperature. To counteract this, metal pots can be lined with polystyrene sheets or plastic bubble wrap to provide insulation against temperature changes.
Choice of compost
This will depend on whether you are creating a temporary or permanent display. If you are creating a temporary display for annuals or tender plants which you will remove from the pot to keep indoors over the winter, a general use, multi-purpose compost is ideal. This compost is light weight, making the bags of compost and the planted pots easier to handle, and often comes with fertilisers and/or water retentive granules included.
For permanent planting schemes a loam-based compost should be used as this will retain its structure beyond the first year. For most permanent containers (eg containing shrubs or ornamental grasses) John Innes No. 3 compost is a good choice. Ericaceous mixes are available for acid-loving plants.
Compost mixes can include organic matter such as coir, composted bark and leaf mould. However, it is important that anything added to a container compost mix is sterilised first. If you add too much organic matter containing living organisms (including earthworms) you run the risk that they will exhaust the food supply from the organic matter itself and start eating your plants’ roots instead. For the same reason, soil from your garden should not be used in containers.
Nutrition
While some multi-purpose compost mixes come with an amount of fertiliser in them, it won’t necessarily be enough to sustain your plants through the whole growing season. Therefore it’s easiest to mix in slow release fertiliser granules when you initially plant up your container. These little pellets will gradually release fertiliser over a long period, usually around 6 months. You can always use additional feeds if you feel it’s necessary (for example if your plant shows signs of a nutrient deficiency), but ensure that you only use inorganic fertilisers. Inorganic fertilisers, unlike organic ones, don’t rely on microorganisms in the soil to break them down and release food to the plant – and because you used a sterile growing media there won’t be as many microorganisms available in it.
Preparing your plants
When your container is ready, you need to prepare your plants for the move to their new home. Make sure the compost you’re putting the plant into is damp before planting. If the compost has already dried out then you may need to mix it with water in a large tub or wheelbarrow to make it damp again.
If the plant’s rootball is dry, soak it in a bucket of water until it’s thoroughly wetted. Assuming the plant is already in a little plastic pot, put the whole pot in the bucket, rather than removing the plant. Once it’s really wet, take it out and leave it to drain for a few minutes before planting.
Putting your plants in the container
Part fill your container with compost, to a depth that leaves enough space above for the deepest plant to fit in. Carefully knock or shake the container a few times to make sure that there aren’t any air pockets in the compost, then press down gently on the surface to consolidate the compost. Check the depth by putting the plant (still in its plastic pot) on top of the soil – the surface level of the compost in the plant’s current pot should be 5-10cm below the rim of the new container (to allow space for watering and mulching). Once you have the compost at the right depth take the deepest plant out of its current pot and put it in place in the new container, holding on to the foliage of the new plant so it doesn’t get caught in the compost (you might find it easier to loosely tie the foliage up with twine if you’re dealing with a large, loose plant). If you’re trying to get it central, make sure you check it from all angles (or get a ruler out and measure it) as it’s very easy to get plants off centre.
Once the first plant is in place, add compost around the rootball, gently pressing down on it from time to time until you reach the correct depth for the next deepest plants. Repeat this process until all the plants are in. Make sure that all the plants are planted to the same depth as they were originally and that no leaves or stems are trapped under the surface of the compost. Don’t firm the top of the compost too much or you can compact it and damage roots.
Water the container thoroughly. Check it again in a few hours to fill in any areas which have sunk a little as the compost settled.
When dealing with hanging baskets you follow the same basic process, with a few additions. If the basket is a wire one which allows planting through the sides as well as the top, you will firstly need to place a ready-made basket liner, well soaked sphagnum moss, or perhaps an old jumper, around the basket to hold the compost. If you are using sphagnum moss, build the layers of moss up gradually, filling each section with compost to hold the moss in place.
To plant up the sides, fill the basket with moss and/or compost to the level you want to put the first plants in at. If you have a ready-made liner (or a jumper!) cut a cross in it large enough to poke the plant through. Take a sheet of newspaper and gently wrap it around the top of your plant, so it holds all the stems and leaves in a cylinder of paper. Remove your plant from the pot and feed the newspaper wrapped tip of the plant gently through the hole. Once the plant is in place, with the rootball up against the edge of the basket, gently remove the newspaper. Continue this process to add all the plants into the side and finally add the plants to grow out of the top surface of the basket, filling all gaps as you go. A final layer of moss can be added to the top of the basket to act as a mulch. Water well.
Let baskets rest in a sheltered spot (stand them on top of a large plant pot or bucket) so that the plants can establish before hanging them; this helps the plants adapt to their new home and build a good root structure before they are hung up and exposed to the elements.
Mulching your container
Adding a mulch on top of the compost in your container can help to retain water, reduce weeds, prevent the compost eroding and give an attractive finish to your container. A wide range of materials are available which make suitable mulches, and you may find that on the smaller scale of container plantings you can justify the expense for very attractive mulches such as seashells or tumbled glass. Just ensure that your mulch is sterile so you’re not introducing any organisms to your container which may run out of food from the compost and start eating your plants’ roots (eg earthworms).
One slight downside of mulching is that you are likely to need to remove it at the end of the season, or at least once a year to refresh the compost. This can be quite a fiddly job as mulches tend to work their way down into the compost. If you use a relatively cheap mulch such a gravel you may be happy to just dispose of it with the compost. However, if you have spent quite a lot of money on a beautiful tumbled glass mulch, you may have to spend a bit of time picking the pieces out of the compost to save your investment!
