Ask the head gardener: How often should I water my pots?

Telegraph

2 days ago

Dear Tom,
I have moved from a half-acre garden to a south-facing terrace. I had never used pots in my previous garden, so now I'm not sure how often and how much to water. I have several huge pots, and some medium ones so far.
– Claire, West Sussex
Dear Claire,
Container gardening is periodically intense but can provide the most amazing riot of colour and seasonal interest, making a small space work very hard in terms of impact. The way in which you water and feed your containers will make the difference between a reasonable display and a spectacular one. One of the features of peat-free compost is that the surface can appear to be dry but, quite often, a little further down into the root ball, the compost is holding much more moisture. Given that watering and feeding have a great impact, here is my guide to tending your containers.
Drainage
Healthy plants grow in compost with a more open structure and better air circulation because roots need that gas exchange in the same way as every other part of the plant. A saturated compost will significantly reduce the amount of gas exchange that occurs within the compost and then will compromise plant growth through root rot. For small trees or shrubs in containers, I would recommend mixing in 25 per cent of horticultural grit to open that structure within the compost and improve drainage.
Containers can dry out readily during the summer but it's also worth considering what happens to your pots during the winter. Saturated, frozen compost will expand and can cause terracotta pots to crack. Raise your pots on pot feet to allow any surplus moisture to drain away, especially during the winter months. For extra protection and insulation, your containers can be wrapped with bubble wrap to offer them a few degrees of extra warmth during prolonged cold spells.
Top dressing
Mulching your containers with gravel or composted bark will not only look great, but will also help to suppress weeds that will compete for moisture, and will help to lock in moisture in the compost. A layer of a few centimetres will suffice.
Active growing season
Many of our garden plants will have an active growing season from around the end of March until the end of October. This isn't set in stone and is in response to increasing light levels and temperatures. When plants are growing rapidly, they need more moisture and nutrition to sustain healthy growth. Water your containers more frequently during this time, with a daily watering during the months of June, July and August.
As the plants become more dormant and slow down, their need for water is drastically reduced, along with the need for fertiliser. It is much better to keep your containers slightly on the drier side during this dormant period to maximise that gas exchange within the root ball. The addition of a liquid feed once a week for your containers during the active growing season will help produce great results. Initial growth should be encouraged by a weekly feed of seaweed fertiliser, followed by the application of a tomato feed once a week when the flowers appear.
Watering
Watering is best carried out first thing in the morning when plants are waking up. During the evening and at night, plants are not processing water, so although the compost may be saturated, plants won't use that moisture until the sun comes up.
Try to avoid watering your plants little and often as this will encourage surface rooting, and in times of stress through drought, your plants won't have the resilience that they would if you encourage deeper rooting by saturating the compost to the bottom of the pot. For bedding plants and hanging baskets, your finger is a good indicator to see how much moisture lies beneath the surface. If you detect moisture on your fingertip then there's no great need to water, especially during the early spring, autumn and winter.