The Beginner’s Guide to How and When to Water - a guide for people with new gardens
This is not a straight-forward topic to write about - as you will see - because when it comes to water you need to give the plants as much as they need to establish….and quantifying that is not easy to write down out of the context of your own garden.
Let’s quickly start with the basics - why water at all?
Plants require nutrients from the soil, they require sunlight (to varying intensities), and they require water. Water acts in two ways - to help to power the chemical reactions that underpin photosynthesis in the leaves, and to draw nutrients from the roots to the areas of growth (pulling them up the plant, dissolved in solution, through capillary action).
Therefore to grow, respire, and remain a healthy and viable organism plants each need their optimum amount of water.
Of course outside of a garden (or artificial landscape) plants are not watered. They create complex root structures to draw water from the soil, either growing deeply or more shallowly, to extract water trapped in spaces between soil particles (which prevents water from simply evaporating into the atmosphere).
Therefore why water? It is because when you plant new plants into a garden they do not have an extensive root system of their own with which to collect water. Their roots have been trapped inside a pot and so have a very limited spread (all of which is also constrained in the growing medium from the pot). New plants therefore need additional water to (a) survive and (b) to power the growth of new roots that will allow them to find water for themselves.
What you are trying to achieve with watering
Watering new plants is therefore a balancing act. You want to keep the plant alive (as its capacity to capture water is only from a limited area) but you want to ‘stress’ the plant enough that it recognises the need to grow an extensive system of roots to find additional water to power its growth.
This means that you are not trying to give too much water to the plant (and certainly not so much water that the roots start to rot) but neither are you leaving it too dry so it (and its roots) start to desiccate. Both of these issues will show up as signs of stress above ground - with leaves discolouring (often turning yellow) if over-watered, or wilting if under-watered.
Some rules of thumb for getting watering right
With a new garden and a variety of plants some plants will need more water to establish and others slightly less but generally speaking the advice for watering is:
use an oscillating sprinkler to ensure you water the whole area and don’t miss anything (if you’ve only planted a few plants this is more effectively and more sustainably undertaken with a watering can using collected rainwater)
water morning or evening so that you don’t lose water through evaporation before it can seep into the soil
the soil needs to be damp at least 2cm below the surface - you therefore need to ensure you’ve watered enough to seep into the soil and not just damped down the surface
watering frequency is really difficult to quantify but most designers and nurseries would advise at least 2 weeks of watering every day, 2 weeks of watering 3 - 4 times per week, and then watering when necessary (such as just before plants start to wilt or if there is an extended dry spell); for new plantings, and trees (see below) you need to water daily even if it has been raining - as a light rain shower will not soak sufficiently into the soil
personally though, I prefer to water less frequently than this to ensure that root development is encouraged; this does need some spot watering of key plants by watering can each day and for you to carefully review all the plants every day as well
also trees will require well watering to ensure their survival; a good piece of advice here is to give them a bucket’s worth of water every day for their first 2 summers (using less in spring and autumn and no extra water needed in winter); this is because they will have a lot of top growth and almost no root system until it establishes itself so you are providing them with all of their water (because the root system has not developed in situ from seed);
providing you’ve designed the garden properly - with the correct selection of plants - they should establish, and find their own water, relatively quickly; additionally a mulch applied to the surface will reduce water loss through evaporation (and will reduce weed growth that would be triggered by regular watering)
finally, and most importantly, common-sense is needed to flex these requirements as necessary, to help to ensure your plants survive and thrive (for example if plants start to wilt between waterings water more often)!
Watering sustainably
We are all trying to conserve water.
New homes often come with a rainwater harvesting tank and these are the best systems to irrigate your garden from. Rainwater does not contain excess minerals and does not require energy to produce and transport.
This will not be available to everyone with a new garden though. If using the domestic water supply then the all of above recommendations still apply - but you need to be conscious of the need to minimise water use, recycle where you can, and keep an eye out for local regulations in the event of a summer hose-pipe ban. Within hose-pipe ban regulations there are often provisions for watering new gardens but these change depending upon your local water company and as advice is updated each year - so you need to check this if it affects you.
Once a garden is established then try to use rainwater to water wherever possible - but if plants are selected properly they wont need gallons of extra water to remain alive in a UK garden. Grey water can also be used once plants are established - but use this sparingly and limit this to very dry spells to minimise any chemical build up in the soil.