Thank you for your question. I am a bit confused, because I’m not sure if you’re asking about leaving the needles as mulch on your garden, or whether you’re wanting to know whether to put the needles in a compost heap/bin after you’ve removed them. As mulch, needles protect the soil from rain and snow compaction, retain soil moisture, may prevent weeds from developing, acidify the soil as they decompose, and eventually return nutrients to the soil, just like any other organic mulch. Because of their acidic nature, they are helpful as a mulch for acid-loving plants such as blueberries and rhododendrons. In nature, where no human is raking them up, they help with soil texture as they break down—but it can take years. Needles in compost have the same traits, but with the same long-term decomposition timelines. So, they can’t keep up with leaves or ‘softer’ plant structures, and will still look and act like needles far longer. Perhaps you can clarify, and I can give you links to Extension articles with more information. Thanks!

I wanted to know if I should leave the needles where they fell and in the concentration as they fell as mulch on the garden. I had been advised to "leave the leaves" from the surrounding maples as they would break down easily, but had read conflicting opinions on leaving needles (some said removal due to the needles forming water shedding "mats" and acidification and other opinions were to add compost on top of the needles and let them decay as the acidification was temporary).  

The tree is a Sierra Redwood Giant Sequoia and I wanted to be mindful of the right plant in the right place.  If the ferns and bleeding hearts are not going to be happy beneath a sequoia, I wanted to move them.

Thank you for your help.

Thank you for clarifying. First, I’m surprised it is a sequoia, because they are typically found only in Central California (https://oregonstate.edu/trees/conifer_genera/giant_sequoia.html). But, your neighbor or his/her predecessor may have brought it to Oregon. But it appears that the ferns are natural ‘neighbors’ on this list: http://marinmg.ucanr.edu/Marin_Master_Gardener_Help_Desk/Leaflet/Redwood_trees_are_horticultural_marvels/ Although bleeding heart is not on the list, it prefers part shade and moist, but well-drained soil: http://www.gardening.cornell.edu/homegardening/scene9f1f.html So, the needles should not be an issue, but the tree’s ‘water greediness’ may be. Leave everything as is for a year, and reassess next fall. Good luck!

You may have already discovered this publication, but it is very helpful for gardeners wanting a native plant environment: https://www.oregonmetro.gov/native-plants-willamette-valley-yards-booklet

Thank you for your help. Much appreciated!

Welcome! One more resource: https://workspace.oregonstate.edu/course/landscaping-with-native-plants-online-course?hsLang=en

Thanks!

Thanks!

Thanks!

Welcome!