Spring gardening: pruning, potting, sowing

Spring pruning of plants in pots and planters

Overwintered container plants will need some care before they can move outside from May: you will need to remove any pale winter shoots, prune the plants, then repot them and add fertiliser. This is to thin out the plant and remove any old, withered or crossing stems. Pruning can also help keep plants nicely shaped. The tool list for this task is simple: all you need is a pair of secateurs. If you are pruning back thick stems on large tub plants, you may also need heavy-duty pruning shears.

When can you start pruning plants?

There is no specific season for pruning plants, but it should always be done before the main budding of new growth occurs – pruning young growth at a later stage will only rob the plant of its energy reserves. Container plants may produce weak, spindly shoots in winter. These long, tender, pale green or yellow shoots form when a plant doesn't get enough light, and they should always be removed. Any plants which overwinter in a conservatory or a cool, bright place are likely to grow shoots early in the season. You can thin these plants out until the end of February, but after this, they should be moved to a bright, warm location; otherwise, they will begin producing spindly growth again.

If you have plants that have overwintered in the dark, prepare them for spring by placing them in a bright position from the end of March. This gives the plants a chance to start growing before they are moved outside in May; if the plants are kept in the dark for too long, the flowering time will be delayed.

How to prune plants correctly

In addition to the spindly shoots we have already mentioned, you should also remove any old, withered or damaged branches. Be careful not to leave any stubs behind – you should cut the shoots directly at the main stem or a thicker side branch. Branch stubs will usually dry out and not sprout again.

Geraniums, fuchsia, leucanthemum and summer-flowering container plants will produce blooms on new growth and can be cut back more severely, to two to four buds or a branch length of 5-10 cm. This will make sure they remain compact and bushy. Oleander, on the other hand, produces blooms on shoots that are two or more years old, so take care if you want to prune yours because it has become too large. 

We recommend pruning in stages, reducing the size of the whole plant over a couple of years. Patience is a virtue here, as otherwise, your oleander will have no flowers at all for at least a year. Important: If you have shrubs in planters that have got too large, don’t just crop them to a uniform height all over: either cut off whole branches or trim side branches by a third – this means the plants will retain their shape.

One simple rule to remember: the harder you prune them, the longer they’ll take to flower.

Potting and repotting made easy

Plants in pots or planters will one day outgrow their accommodation and need to be moved to a larger container; learning how to repot a plant is simple. Older container plants may need to be potted up every two to three years depending on growth, while younger plants can need repotting every year. When the plant has become potbound – i.e. the root ball is compacted with root growth, and the roots have begun growing out of the drainage holes – it's time for a change! 

The pot size is not the only issue, though: even if not yet potbound, all container plants require new soil regularly. This is because the growing medium in any container will become depleted, losing nutrients and stability over time so that it quickly turns sludgy when it rains. By adding fresh soil, you give the plant renewed nutrients and improve water retention so you need to water it less often. Balcony plants also need new soil every year, whether they have been overwintered or newly purchased.

Time and preparation: What you need for repotting plants

You can also repot overwintering balcony plants into fresh soil from mid to late April. It is best to do this as soon as you have taken them out of their winter storage location and pruned them. Afterwards, you can move the plants to a brighter location.

Finding the right soil and suitable containers

Selecting the right kind of soil depends entirely on how long the plants will stay in the pot. For annual plants, you can use a good own-brand, peat-free soil from a garden centre. If a plant is going to stay in its pot for longer, e.g. in large planters, we recommend you use a high-quality brand of container or potting compost. You can also use multi-purpose compost. You only need specialist soil if you will be planting multiple plants into one container. Citrus plants, hydrangeas or azaleas are exceptions, as they always need specialised acidic (or ericaceous) soil.

When selecting a suitable plant pot, make sure that it has a broad base and is no taller than it is wide; this means it cannot tip over easily. Adding gravel for drainage adds weight and makes the container even more stable. Clay and terracotta are classic choices for pots. They are heavy, but have many advantages: in sunny locations, they protect roots from the heat, while in the winter, they keep plants safe from frost. However, if you leave the pots outside over the winter, make sure they don't take in water, as this will mean the clay is no longer frost-proof and might crack in freezing conditions.

If you like the look of stone and terracotta but would prefer a less expensive option, there are many plastic pots available in similar designs. Plastic pots generally keep the soil moist for longer because the water can't evaporate through the sides. Don't forget to make sure that the pot has a drainage hole. Waterlogging hurts all plants.

Here is how to repot your garden plants:

• The new pot should be two finger-widths wider than the old one.
  
• For larger plants that you don't want to move to a larger pot, you can reduce the size of the root ball. To do this, remove the plant from the tub and cut the root ball with a long knife into a cube shape. Then replace the plant in the old pot along with some fresh soil.
• Place a shard of ceramic over the drainage hole, topping it off with a drainage layer of expanded clay.
• Place a cotton cloth or newspaper on the drainage layer so no soil seeps in.
• Add soil, place the plant in the pot and fill the container almost to the rim with more soil.
• Press down gently on either side of the plants with both hands so that there is a distance of 2-3 centimetres between the surface of the soil and the top of the pot so it can be watered easily.

Tricks to make potting and repotting easier

• The drainage layer should only be a few centimetres thick; otherwise, it could work too well and drain the pot entirely. 
  
• Where possible, place the tub on flat stones or pot feet so that ants can't get inside easily and water drains effectively.
• Leaving space between the top of the soil and the rim of the pot for watering is especially useful for thirsty plants; simply pour in a good dose of water which will be held here like a reservoir and will seep gradually through the pot.  
• Mulching also works with container plants. Gravel is a proven choice, but grass cuttings can also be used.
• Slow-release mineral fertilisers are the best option: organic fertilisers often work too slowly in balcony boxes, and there is no need to improve the soil for annual plants.
• Self-watering pots: automatic self-watering from the built-in tank only becomes effective after four weeks, as plants need that long to take root. Until then, you will need to water plants in these pots as normal.

Sowing seeds in spring

The selection of young plants on offer in garden centres can't compare with the variety of options available as seeds. Seed packs are also much cheaper than plug plants. And there is one more advantage: if you are looking for more unusual plants, seeds are the right choice because many species you can get as seeds are simply not available as plants. You can find out all you need to know about sowing seeds here.

You should generally only use specialist seed compost, as this is low in nutrients and will make sure your seedlings are not sluggish – they will be forced to grow lots of roots to source the nutrients they need. The resulting root mass will see seedlings grow into strong plants in the right soil.

You will not need seed compost if sowing directly into the earth outside. Summer flowers, in particular, can be sown directly into beds from May onwards, eliminating the need to start them off in trays on your window sill. For root vegetables such as carrots, direct sowing is the only option, while other vegetables that need warmth to germinate must be started indoors (e.g. tomatoes or aubergines).

If you are planting seeds indoors, clean old seed trays with hot water since young plants are very sensitive. Fungi can damage and even kill seedlings.

How to sow seeds

The size of the seeds will determine whether they should be sown in individual pots or propagation trays. Large seeds can be sown into pots individually or in pairs to get a good start until they are planted out. Small seeds are sown in flat propagation trays, so they can grow in large numbers. Here’s how to do it: half-fill the tray with soil and press down gently with your fingers. Now fill the tray up completely so that the soil in the middle is heaped significantly above the rim. Then skim off the excess with a ruler. You should hold the ruler at a slight angle of about 45° while doing this – and be sure to slide it beyond the edge of the tray. This will automatically compress the soil. Finally, press down gently on the soil with a wide piece of wood so that it bulges slightly towards the edges of the tray. Now, scatter the seeds directly from the package, distributing evenly, and sift some soil over them. Tip: Mix tiny seeds such as begonia seeds with bird sand and spread the mixture across the tray using a tea strainer. As soon as you can grasp them firmly by the seed leaves, the seedlings from the tray should be pricked out into small pots before they can be planted outside. You should only prick out the strongest seedlings.

The best way to water seeds is with a watering can with a fine rose. Now, cover the seeds with a clear cover. If you don't have a propagator, you can use a plastic sheet or some plastic wrap. This keeps more moisture in with the seeds.

Seedlings often grow towards the light and can become crooked, but here’s a simple trick to get your seedlings growing straight: place seed trays into a cardboard box with one side open. Stick a piece of aluminium foil into the box so that the incoming light is reflected off it. Seedlings grown in a lightbox like this tend to be significantly stronger.

Summary: The garden in spring

• At the start of the new season, check your potted plants and remove any old and withered shoots, as well as any stems which cross over each other.
• From the end of March, move container plants that have overwintered in the dark to a bright, frost-free location, where they’ll start to grow again.
• From May, you can put tubs and potted plants outdoors again.
• The harder you prune them, the longer they’ll take to flower – so don’t cut potted plants all the way back in one go; do it gradually.
• Repot young container plants every year and older plants every two to three years. At the latest, it’s time to repot when roots are growing out of the drainage holes.
• Choose the right planter: clay or terracotta pots are heavier but protect plants from heat and frost. Plastic pots retain moisture in the soil for longer. All pots should have a drainage hole.
• Don’t forget to include a drainage layer when potting and repotting so water drains away properly. 
• When growing from scratch, large seeds can be sown directly in a pot, individually or in pairs, while small seeds can be planted in large numbers in a flat seed tray.