here is another flax. It has the same leaf problem, but doesn't have leaves that are getting pink like the previous one.

When did you plant them?

That could be a soil nutrient problem or a soil moisture problem or a planting problem.
If the plants roots are unable to stretch out and take in moisture and nutrients even the best soil in the world will not be of any help.
If the soil lacks adequate levels of moisture the plants roots will not be able to uptake any nutrients in the soil. If the soil is too wet the same thing happens.
If the soil the plant is trying to grow in lacks nutrients the plant cannot uptake what is not there.

lack of proper water management.. including deep soaking of the soil.. and mulching over black soil ...

not only is the soil color taking up and retaining heat late into the night .... it is sucking moisture out of the leaves themselves .. the heat retension is a problem.. as many plants can recover at night .. when the sun goes away.. unless its roots stay too hot to do the job ....

the plants looked baked ...

i suspect recent transplants ... and if so.. it is NOT a nutrient issue ...

do NOT fertilize an already stressed plant ...

also.. its hard to tell from the pix.. but are these on a slope.. if so.. that complicates deep watering also .... as it looks like the water is running away.. before soaking in deeply ....

ken

the reason I suspect it is nutrient problem for the first picture is that you can see a leaf gets pink. What do you think? I am not sure if it is the case and what kind of nutrient I need to add.

it is not on a slope. But the soil is clay, so I dig a big hole and use compost+coffee ground (1:1) as the soil. The first one is a little better probably it starts to get some shade at 2-3pm. The 2nd one is very bad, it has no shade until probably 6pm.

Probably it is too hot and I need to add some shade and mulch.

Flax - Phormium tenax - is an incredibly drought tolerant plant. It is also not the slightest bit fussy about soil conditions, including nutrient levels, other than requiring very good drainage. The hybrids are a bit more fussy than the species and less tolerant of extended droughts, heavy soils and intense sun.

Daily watering may be excessive....especially if the soil is somewhat heavy or drains less than ideally. Digging a large hole and filling with compost in an otherwise clayey soil is just creating a large bathtub - you are drowning your plants!! If your soil needs amending to loosen or lighten the clay, you should do so over the largest possible area - NOT individual planting holes. Otherwise, dig a wide and quite shallow planting hole and locate plant so the top of rootball is above grade. Then use the removed unamended soil to mound up to top of rootball, creating a mini berm. You can use the compost as a mulch or topdressing.

Pink coloration is not out of line for these plants as many colored and variegated hybrids exist and there is some genetic leanings towards colored foliage. Usually considered a problem-free plant for any part of CA - I'd look first to watering issues before any sort of nutrient problem.

insert finger.. or use a trowel.. and find out about how water moves thru YOUR soil ... dig done an inch or two.. and find out ....

guessing is useless ...

and only you.. can define such in your soil ...

but do let us know ...

i NEVER fertilize a stressed plant .. or when i used ... to they all died...

finally.. a plant planted.. a few months ago.. is usually NOT fully established... the drought capability of an ESTABLISHED plant.. can not be equated to a recent transplant ....

but your base problem remains... IMHO .. the leaves are not getting enough water.. either you arent getting water in to the root zone ...

or there is so much water down there.. the roots rotted off ... so not enough water is being processed for the leaves ...

and.. as far as i am concerned.. the mulch would still be a plus ...

ken

thanks for your suggtion