Learn Hardcore Japanese: nedumari ga susumu ni turete, mizuhake ga waruku naru. - As root binding progresses, the soil drainage gets worse.

In this sentence, 根詰まり（ねづまり） is a gardening term meaning a plant’s roots have become too crowded in the pot or soil, so they are packed together and have little room to spread.

In English, this is often described as being root-bound or pot-bound.

So 根詰まりが進む means something like:

the root-bound condition gets worse
the roots become more crowded
root congestion progresses

This is different from some other words with 詰まる / 詰まり, which can mean to be clogged or to be blocked in other contexts.

Why is there a が after both 根詰まり and 水はけ?

Because the sentence has two parts, and each part has its own subject:

根詰まりが進むにつれて
→ root crowding progresses
水はけが悪くなる
→ drainage becomes worse

In Japanese, the subject of each clause can be marked with が.

So this is not strange or repetitive. It is just:

根詰まり is the thing that progresses
水はけ is the thing that becomes worse

What does 〜につれて mean?