Pictures of the situation would help but don’t put irrigation touching the plants. Put it a foot or so away from newly planted plants. Whether in front or behind is up to you. The plants don't know the difference. Maybe someone in California can say whether Bougainvilleas even need irrigation there. I’ve never seen them in Europe being irrigated.

you are watering the root mass.. not the plant you see ... so .. most likely.. you could put it a foot away.. and still accomplish your watering...

DEPENDING on you soil type and how water flows thru your soil... have you perced your soil.?? do you even know???

https://duckduckgo.com/?t=ffab&q=perc+garden+soil&iax=videos&ia=videos

what flora said about the necessity of watering....

but. to be sure.. you MUST water new transplants for the first year.. and in drought in the second.. but afterwards.. many plants should be well established..meaning they have an established root mass.... and be able to care for themselves after that.. unless you are zone pushing and playing the odds ...

ken

ps: the person who sold you the irrigation.. should have told you about percing.. unless it was bigbox of course ...

They're not newly planted. Actually, I've had them for about five years but they weren't thriving. They're mostly woody stems, and I wanted a hedge. I called a new gardener and he said it was because they weren't getting any water with the drip line in front of them. He moved it back a few inches. Then a second gardener said it should be in front of them, and he moved it there. So now I'm totally confused! The line is covered with mulch so a photo wouldn't help. :(

Since they're not newly planted, does it matter if the line is touching them? I've never heard of percing. :( And I'm still wondering why they haven't filled out in all this time!

Pictures of the plants, not the drip line, are what we need to help us to see what the problem might be. Irrigation in front or behind is irrelevant to plants. They don't have a 'front' or 'back'. Roots radiate all round so your gardener is talking nonsense. The advice about water not touching the plants is nothing to do with how long they've been in the ground, it's to do with applying water where the roots are and not keeping the trunks damp, which can lead to fungal issues. As Ken said, you water the root zone, not top growth. Anyway a five year old Bougainvillea shouldn't need to be nursed with constant water. You say they are woody. Have you pruned at all? This plant isn't a shrub, it's a lax woody rambler that wants to scramble upwards. To make it into a hedge it needs training and pruning.

Im in Zone 9b and don't irrigate my established bougainvillea.

@Louisa I am going to insist along with the others that you show photos of the plant, because we need to first figure out is the problem here a failure to deliver water to the plant. If it looks dry and underwatered, then my solution to that will be to wrap the base with soaker hose that is tied to a rate limiter so you know the precise amount of water delivered across the base.

If the plant does not have a watering issue, then let's not focus on the water delivery.

Did your two gardeners agree that the plant appears to be underwatered?

I'll take a photo tomorrow. Actually, these are dwarf bougainvillea: Rosenka.

The second gardener didn't say if they needed more water;

he just moved the drip line to what he thought was the right place.

Over watering is more likely to be a problem with bougs than under watering. Mine did perfectly fine through our awful multi year drought, but lost all their leaves this winter when it rained non stop for 4 months.

@drinkmorewater I have my one Bougainvillea in a container and never water it. It doesn't like that. These plants enjoy getting watered a few times a week, but they want very well-drained soil. If she has an in-ground planting and the percolation test of the area shows it to be slow-draining, then sure it might be overwatered. But from what I am understanding this plant is getting water from a single emitter on a drip tubing system, so I am struggling to see how that could saturate the soil.

@Louisa This is your variant. So much for being "dwarf". :)

@Louisa I just did a percolation test for @ken_adrian Adrian MI cold Z5 in this thread. You might want to see how I approached it, although it looks like I did not dig the ditch quite as deep as the test requires (mine was eight inches deep and the test asks for 12 inches in the test ditch).

Ask your gardener for the following information and convey to us:

1) What are the gallons per hour delivered to this plant by its emitter?

2) Is the plant watered only by a single emitter or is there another water source?

3) How long does the irrigation system water this plant, and on what days of the week?

Once you have the percolation test done, we will know if your soil absorbs water too slowly or too rapidly.

Once you have the questions I asked answered, we will know if the amount of water is too much or too little for the soil draining conditions.

Judging water requirements is not simply a matter of checking the soil drainage, measuring the amount and applying a rule. The plant in question and the weather are vitally important factors. You can’t water by numbers and formuli. And several of us here are questioning whether regular irrigation is even necessary for this subject.

@westes Zone 9b California SF Bay Plants in containers have different irrigation needs than in ground, of course. Even the most drought tolerant plant in a container will need to be watered since it has absolutely no other way of getting to water. Established bougainvilleas have an extensive root system (even aggressive) and can take care of themselves better than container ones.

@floral_uk z.8/9 SW UK Obviously you factor in the plant in question. I would add the weather to my list, She should answer the questions I asked and then we might move this conversation to a useful conclusion.

@drinkmorewater I don't disagree that a container plant is more helpless and depends on regular care. My point is this is not a cactus that you can simply water once a month. It appreciates water from*some* source but wants the soil to drain well. A deep watering once every 7 to 14 days probably is enough, but watering twice a week if the soil drains well is probably also okay.

Thank you to everyone for your thoughtful and detailed suggestions! I'm posting

a pic of the rosenka from a few weeks ago (I wasn't able to take a photo today). My regular gardener who'd planted them had put plastic around them to prevent damage to my home's foundation. The plastic has since been removed. The two gardeners who disagreed about the drip line placement came here one time for this problem only. I'll take a current pic tomorrow, and I'll try to figure out the answers to your questions about the irrigation. We had an unusual amount of rain this year, if that makes any difference.

@Louisa More questions to add to what I asked already:

4) Where do you live and what is your plant zone?

5) Describe your weather pattern throughout the year.

6) Applying some common sense, does the soil in which these plants live feel dry or moist between waterings, going down about 10 inches? You want to have someone do the percolation test and I gave you a link to a thread that talks about how to do it. This is very very important for your case. We have no idea if your soil is wet or dry, and whether it drains fast or slow.

Bougainvillea wants to live in dry soil and then be drenched once every week or two. They want the water to drain fast. You probably don't have those conditions.

Also, if you did not figure it out by now, the photo of your variant makes clear that it is the wrong plant for that small wall location unless you are willing to maybe put up a trellis and very actively prune it.

Thank you again for all the information! I'm attaching a pic taken today. I'm in zones 10A and 10B. Weather is mild except for the past few months when we had rainstorms. It gets very hot in the summer. The soil feels dry. I'll find someone to do the percolation test; thank you for that! Are Rosenka roots so aggressive that they can damage plumbing pipes?

@Louisa The ;photo I found earlier of Rosenka must be wrong. I read now that Rosenka typically reaches heights of around 2-3 feet (60-90 cm), and can spread to around 3-4 feet wide (90-120 cm).

That's why I wanted it. I'm tempted to give up on it and plant geraniums instead!

@Louisa I think the questions I asked are worth answering. My guess is the plants are underwatered, but we don't have the data to conclude that yet.

Thank you, westes Zone 9b California SF Bay. I'll see what I can find out. I asked a nursery about this a few years ago and from seeing a photo, they thought the plants were overwatered. I stopped watering for several weeks and it didn't seem to make any difference. Again, I appreciate all your time on this!