How do I know I’m overwatering?

Hi I’m based in London and have no gardening experience. We have had our garden designed and the designer laid out the plants beautifully and told me to water them every 2-3 days for about 20 mins using a sprinkler as the first year of growth is very important.

However I’m worried I’m overwatering. The Amelanchier has already developed powdery mildew which I’ve treated with fungicide but I had to cut back the dead leaves and affected branches substantially. Now today the lavender showed signs of decay at the base. I googled this and it seemed to be root rot (see attached photo). I had watered the plants yesterday but as it was 34 degrees in London today I watered them in the morning today too. The soil does not seem waterlogged under the mulch but this is London (clay) so I’m not sure it’s draining efficiently.

Can someone tell me what I’m doing wrong? How can I tell if I’m overwatering or under watering? I’m scared not to water enough as I’ve been told to but now I can’t see the wood for the trees.

Photo of decaying roots attached.

 

The thing is different plants have different watering needs, it's a good idea to read up on the plants you have and to see the conditions they need.

 

@HackettLad Lavender is a Mediterranean plant growing on free draining sunny hillsides so needs similar conditions in the garden. Shouldn't need watering much at all after it's planted. Mine grow in a sunny pebbly raised bed. They get dead headed after flowering rather than pruned.
I would stop using the sprinkler and use a watering can or hosepipe, so you have more control over the amount of water going on each plant.
I would have a chat with your designer for more specific advice on aftercare and also feeding.

 

Thank you so much. I felt a bit defeated but I know I have to learn. I’ve texted the designer. Just so I understand, does your advice on watering still apply to newly planted lavender? Does it not need extra watering in the first year of planting? Many thanks.

 

I'm looking for decaying roots, but can't see any.

I'd be more inclined to keep a very close eye on things and water plants that start to show the first signs of stress.
If newly planted you are in danger of the root ball drying out while the surrounding soil can still be very wet.

So I'd be watering plants individually as opposed to a drenching every where.
You can then give the whole area a soak once a week if there is no proper rain.

 

thank you so much for your advice! I wish I had taken a proper photo but I didn’t know what I was dealing with. The bottom of the plant has become grey but the top half remained verdant. I looked this up on Google (a classic mistake probably) and it seemed that it was the root rotting. Which in the light of your reply might not have been the case!

 

Regarding rotting roots, the grey bits around the base of the plant look like fallen leaves to me.
Really without digging you should not be able to see the roots.
Lavender leaves do go grey when they die and some leaf loss around the base is normal.

 

Thank you very much. You are totally right. The lack of experience and a benchmark is what is confusing me. If I use a watering can to direct the flow, how much water is enough? Is there a rule of thumb?

 

Probably watering, and explaining watering is one of the most difficult things about gardening.

 

It's very easy to over complicate it, but basically, if the plants look good then everything is ok.
In the unusually hot weather it can make things more difficult, but if everything is looking good early and late in the day, things and probably ok.

 

Can I just add that most plants are grown in peat or peat-substitute, so the roots can struggle to get out of that initial rootball into the surrounding soil. That's why it's really important to water slowly, gently but thoroughly into the rootball for the first year. Some plants settle in quickly, others can take ages and most take longer to make the transition from peat /PS to clay. It can be an interesting experience to put a sprinkler on a patch of dry ground for 30 minutes, then take a trowel and dig a hole to see just how deeply the water has penetrated

 

Thank you all for your fascinating insights. I’ll be honest. I was about to give up and ask a professional gardener to deal with it but where’s the learning in that? Everybody’s comments have helped me gain a better understanding of this fascinating discipline and I’m super grateful.

 

My first take on watering the garden was "Wait, Observe, Adjust"

1. Wait
No need to just water away if you dont know the results. Just sit back a little and watch your plants

2. Observe
I've made it a habit to go into the garden at least once per day. Doesn't have to be a long tour. Just a quick walk around where you can see any differences to yesterdays (our last weeks) round. Some plants get bigger. Some don't. Some get eaten by slugs overnight und when the weather is hot and dry you will see that some plants will start hanging around like a teenager with emo-syndrome. That would be your cue to do something.

3. Adjust
Wether its watering, hunting slugs or pruning some roses that finished blooming. Once you get a feeling "whats normal" and what isn't, you can help those plants with their specific needs.
And once you get the hang of it, you'll know in advance that a current dry spell will be too much for some plants to handle and water them before they get dried up too much. But that feeling comes naturally and depends on what kind of garden you have. Some garden herbs in tiny pots or the perfect lawn (TM) will need a lot more care than a 15 year old rhubarb and a patch of thyme.