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The Secrets of Effective Watering

April 25, 2010 17:21


Of all the skills a gardener needs to acquire, probably the single most important one is watering. It's also the skill that new gardeners often find the hardest time to acquire.

Many new gardeners know (of course) that a plant needs water to survive and water them every day, only to end up 'killing them with kindness'. But plant roots also need a good supply of air, if a pot is too full of water it pushes the air out and the roots start to rot.

Watering will to a large extent depend on the plant. For the vast majority of plants on the nursery we use a technique called 'wet/dry cycles'. What this means is that we leave the plant to dry out to a certain extent, then give it a thorough watering and leave it to dry again before repeating.

The toughest part of this strategy is judging when a plant is dry. You could, of course, wait until the plant goes limp, but it's best to give the plant water before it reaches this extreme stage. Other than this there arfe basically two techniques you can use: compost colour or the weight of the container.

With many brands of compost you will notice that the compost changes colour when dry. When wet the compost will be very dark brown, if not black in colour. As the plant dries the media will fade to light grey. You will probably also notice the compost becoming dustier as it dries out, though this may not be the case when a plant has been in it's pot more than a few months. You do need to bear in mind, though, that with a newly potted plant in hot weather the top surface of the compost may dry out through evaporation whilst the rest of the compost is still wet. I always recommend extra caution with newly potted plants.

If you've ever picked up a bucket full of water you will know that water is heavy. A plant pot which is full of water will, therefore, weight more than an a dry one. Using weight to assess dryness takes a bit more skill than looking at compost colour, but it can be an effective technique with hanging baskets and well filled pots where it's not possible to see the compost. The skill comes from the fact that different sized containers will naturally have different weights anyway, and different composts may also vary in weight (a soil based compost such as a John Innes type will weight more than a peat based compost). You will need to learn this technique by experience.

There's one more factor that can help you determine when a plant is dry: time. Get to know your plants and how frequently they need watering. A hanging basket in summer will probably need watering daily, the same basket in winter only once a week. The more you practice watering the more you will learn each plants requirements.

So, when you've established that your plants are dry, how much water should you give them? Here's in interesting little experiment you can do: fill an empty plant pot with compost fresh from the bag. Leave the compost level a little below the rim of the pot, as you would when planting a plant. With a watering can or hosepipe, fill the top of the pot with water until it starts to overflow the side of the pot. Leave the water to soak in for half an hour, then tip pot out. You will probably see that the water has barely soaking on more than an inch.

What this teaches us is that a dry pot will need a considerable amount of water to thoroughly soak it. This is somthing to bear in mind when watering a newly potted plant, or one which has dried out to the state of goung limp. For watering in on the nursery I usually recommend filling the compost to the rim at least three times, letting the water soak in between fills.

So, if that's what I recommend for a thoroughly dry plant, what about one which is dry enough to benefit from watering, but is not completely dry? For this case I would simply fill once to the rim of the pot as a starting measure.

From here you can modify the exact amount as you get used to your individual plants requirements. And I'll repeat myself: get to know your individual plants and what their requirements are. Like children all plants are unique and have different requirements, learn what they are and they will flourish for you.


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