For peak health and vigour,-grown plants must be correctly potted, and then regularly potted on and repotted, as necessary.
U sing the correct type and size of pot and the rightcan make the difference between a healthy plant and one that fails to thrive. There are three forms of porting: up consists of moving a , rooted or newly divided section into its first indi-vidual pot.
on consists of moving a plant that has outgrown its pot into a slightly larger one. involves replacing old, worn-out compost with fresh, but re-using the existing pot – often done with large plants.
Choosing the pot
A standard pot can be measured by the diameter of its rim or by its height – both figures are the same. So-called half-, which are not as deep as they are broad, are ideal for plants with shallow and those with a low growth habit, such as alpines. Round are the most common but other shapes are available, many with matching saucers and drip trays.
Plastic pots have now largely replaced clay ones; both have ad-vantages and disadvantages. You can use containers – bulb bowls, for example – withoutholes but to prevent waterlogging, pots with holes are far safer. Plastic pots are cheap, easy to clean, light, and available in various sizes and colours. Many are the colour and shape of clay pots.
Plastic pots are non-porous, so they don’t absorb moisture from the potting compost, and they are essential for capillarysystems. They are smooth so don’t cling to them, making potting on and much easier. Plastic pots are also flexible so any bonding can be eased apart.
Clay pots are much heavier than plastic ones so pots are less likely to fall over – especially when tall, unstable plants are grown in lightweight potting compost – but this also means that larger pots are difficult to move. In addition, not all clay pots are frostproof.
Before use, clean used pots in warm, soapy water, scrubbing off any lime deposits. Soak clay pots first, so they don’t dry out new potting compost.
Most clay pots have a large centralhole. To prevent potting compost falling through and roots blocking the hole, and to ensure good drainage, cover the drainage hole with a layer of crocks (pieces of broken clay pot) or clean pebbles – especially if the pot is over 12cm (Sin).
Most plastic pots have several small drainage holes and so don’t need ‘crocking’. Never crock plastic pots placed on a capillarysystem.
Place enough slightly damp pot- ting compost in the bottom of the pot so that when the plant’s roots rest on the potting compost, the top of the-ball comes to about 1-2.5cm (’/t-lin) below the pot’s rim, adjusting as necessary. (The smaller the pot, the less space is needed between the surface of the potting compost and the rim.)
Position the plant centrally and add more potting compost around it, until flush with the top of the root-ball. Gently tap the pot against the side of the table to settle the potting compost, but don’t firm potting composts with the fingers as this may damage roots or lead to waterlogging.
Once potted, water the plant lightly – damaged roots quickly rot if the compost is very wet.
Set the root-ball centrally on the potting compost so the top is 1 cm (Kin) below the base of the rim. If necessary, gently angle the plant to correct any sideways list that may have developed. Fill the space be-tween the root-ball and pot with potting compost and lightly cover the top of the root-ball with pot-
A plant is usually potted on when it becomes ‘potbound’ – its roots fill the pot, exhausting the potting compost. Such a plant makes little or no new growth and the potting compost dries out rapidly. A sign of being potbound is roots growing through the drainage holes.
Pot on young plants and those that haven’t reached optimum size into larger pots annually, in spring or early summer. Quick-growing plants may need potting on twice or more during a growing season.
The potting compost should be just moist. Place one hand over the root-ball with fingers spread out either side of the main. Carefully turn the pot over and tap it firmly on the base with the other hand to dislodge the root-ball. If necessary, tap the side of the pot against the edge of a table.
If the root-ball still sticks, use a long, thin-bladed knife to slice carefully around the edge of the compost. If necessary, poke a stick through a drainage hole.
Select a new pot about 2.5cm (lin) wider than the existing one for small to medium sized plants, or up to 8cm (3in) wider for large ones. Put a 2.5-5cm (l-2in) layer ‘ of potting compost in the base, depending on the depth of root-ball.
To avoid damaging the foliage orof fragile plants or those with a spreading habit, prepare a mould of compost by first ‘potting’ the old, empty pot in the new.
Many established plants that have reached their required size need new potting compost every year or so if they are to remain healthy, but not a larger pot.
Remove the plant from its pot as before. If the roots are fairly loose, gently tease away some of the spent potting compost and cut away a few old roots. Return the plant to its pot as above, and fill with fresh potting compost.
If the root-ball is hard and crammed with matted roots, slice some off with a sharp knife. Root, however, does weaken the plant slightly.
To revitalize an established plant without, gently scrape off the surface layer of old potting compost, using a small fork or spoon. Try not to damage the or roots. Replace with fresh potting compost and gently tap to firm. Water in as before. Alternate top dressing with repotting.
Incorporating a moss pole
Moss poles – long plastic or occasionally chicken wire tubes covered with moss – are used to supportwith aerial roots such as Swiss cheese plant,
and certain philodendrons. They are too wide to be pushed into the potting compost and must be inserted during potting.
Position the root-ball off-centre in the new pot. Insert the moss pole upright and as deeply as possible behind the plant, then fill the pot with the new potting compost. Tie stems to the pole with soft thread until the aerial roots grow into the moss.
A final top dressing of gravel or limestone chippings is attractive. Gravel and chippings are available in many colours and sizes from garden centres, builders’ merchants, DIY centres and tropical fish stores.
, succulents, hairy-leaved and alpine plants may rot if their or stems come into contact with moist potting compost, so they benefit from a gravel or chipping top dressing.
Give outdoor pots a top dressing of gravel, chippings or wood bark chips to retain water, improve appearance and deter weeds.