Potty about Plant Pots – Which ones are Best?

Friday, April 23, 2010 by Jeremy Dore - Categories: gardening growing pots
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To most people plant pots are just throwaway items – flimsy bits of plastic packaging for houseplants bought from a garden centre or DIY store.  To gardeners, however, plant pots are an essential part of raising plants from seed - which often predominates the early parts of spring when the ground is still too cold for outdoor sowing.  Choosing plant pots and containers is something we may not give much thought to but there are a surprising number of options and choosing the best types can make a big difference to the success of young plants...

Seed Trays or Plant Pots?

Seed trays are the traditional way to start indoor plants and they are very economical on space and soil.  However, the tray depth is rarely more than a couple of inches and little seedlings soon outgrow the cramped conditions, needing to be ‘pricked out’ into pots while still small.

An alternative approach is to sow several seeds into each 3 inch (diameter) pot.  Once they are a couple of inches high you have a choice:

• If the seed is cheap you can simply choose the strongest looking seedling to grow on and remove the others. This is best done by snipping them off with scissors at the soil level because pulling them out can disturb the roots of the remaining seedling
• For more expensive seed such as peppers, the extra seedlings can be pricked out into other pots in the same way as from seed trays.
• Some herbs can be raised with several plants together to make them economical to grow.  I usually grow about 5 basil plants per pot and just ‘pot them up’ as a group when they need more space.

Potting Up

Most plants will outgrow the smaller pots in which they start life and ‘potting up’ is the process of transferring them to larger pots to give the roots sufficient room to continue to grow.  If the plants are destined for the garden then you may be able to harden them off and plant them out before they need this but most plants will need potting up at least once.  To do this choose the next size pot, add some potting compost (called ‘potting soil’ in America) at the bottom, position the plant so the top of the root-ball is still level with the top of the pot and push soil down the sides firmly until it is well supported.

As well as giving the roots more room to grow potting up serves a second very important purpose.  Even the best potting compost gradually loses nutrients as it is watered day after day.  By potting up plants every few weeks they get a fresh supply of new compost with plenty of nutrients to help sustain growth.  If your plants start to show signs of nutrient deficiency such as less vigorous growth or lighter patches on leaves then it is time to give them some fresh potting compost.

Putting Down Roots

Getting plants to grow downwards is as important as the growth above soil.  When they are planted out it will be the ability of the root system to access moisture and nutrients deep in the soil that will help them grow well so containers that have more depth can really help.  There are several commercial products that encourage strong downwards root growth such as Roottrainers which have a ribbed structure to the sides so that roots find it easier to turn downwards.   These work particularly well with peas, beans and sweet corn all of which benefit from deeper roots before planting out.

On a smaller scale I have had much success with raising plug plants.  Smaller seedlings such as lettuce and flowers seem to be well suited to raising in these little modules and they are so easy to produce because the trays are compact and self-watering.

Biodegradable

For plants that don’t like having their roots disturbed a very effective approach is to use bio-degradeable pots.  These can then be planted straight into the soil and the roots will just grow through them. Various types are available but steer clear of peat ones because of the environmental impact - alternatives include recycled fibres, coir and even dried cow manure!  The main problem is that you can’t pot them up with fresh compost so I think these are best used for fast-growing plants such as squash that will be hardened off and planted out within a few weeks.

It is easy to make your own biodegradable pots.  There are simple instructions available for making pots out of newspaper but they usually need a firm tray to keep them upright and in my experience they are hard to make with enough depth for many seedlings.  An alternative is to use cardboard tubes stood upright in a tray with compost stuffed in as they provide better depth.  I use these for peas and beans in a similar way to roottrainers.

Recycle and Reuse

You can often reuse perfectly good plastic containers rather than sending them to landfill:

• Almost any plastic container can become a plant pot as long as you punch plenty of holes in the bottom for good drainage.  This is important because soggy roots can’t get the oxygen they require and that will stunt growth.
• Many thousands of plant pots and trays are thrown away every year by people who buy their bedding plants from garden centres.  Just ask any neighbour you know who does this and you can have an endless supply of perfect pots with perfectly fitting trays which make them easy to move when hardening off.
• Old guttering can be used to raise peas and beans.  Once they are a few inches tall you can slide the plants out of the guttering into a trench for planting.  It’s a little tricky the first time you try it but it works well for succession sowing where the plants will be in the ground quite quickly and so don’t need a lot of depth for roots.

Over To You

Some plants such as root crops should almost never be started in pots but others, like tender basil, do best in pots on a sunny windowsill rather than planted outside.  You can mix and match - I grow some tomatoes for outdoors and others in large recycled pots in my greenhouse.  The trick of course is to experiment and work out what each plant type likes best. 

Do you have your own perfect containers for raising a particular plant or have you found a good way to use recycled items?  Please do add your ideas and tips below...