It’s hard to give any answers without photos.

When was the last full repot? What type of soil? Drain hole? Do you flush the soil when watering?

I know. But I don't have a camera, at least not a digital one. It just looks like a nice healthy schefflera. Last full repot must've been 5 years ago. Combination of bought plant soil + nice soil from my garden, which my indoor plants seem to love. Well, I am not sure what you mean by flushing the soil. Yes, there is a drain hole. This plant has been happy & problem free for years!

Could it still be recovering from sort of stress and eventually it will start making new leaves? Thanks for your interest, Dave.

It sounds like it got too dry to me.

@Tiffany & Dave. Thank you kindly for your input. Whether it got too dry or too wet, I don't know. I guess I have to repot. Another job for summer! I do not know what 5:1:1 is, though.

I added a bit of garden soil because my soil, after years of TLC, is so rich and full of good things that simply aren't to be found in a bag, as far as I can see. Is "potting soil" the same everywhere? Is there some kind of standard content?

Your garden soil is good for the garden, but unfortunately it doesn’t belong in a container.

The way water acts in soil in the earth and in a container are very very different.

If you have the time and interest, this link will fill you in on how and why container soil choices are very important and how water behaves in a container.

https://www.gardenweb.com/discussions/2842847/container-soils-water-movement-and-retention?n=8

@Dave. OK. Thanks for telling me that. I'll read the link.

Happy to share what I do. I agree with Dave if one is thinking about grabbing a few shovels of lifeless, infertile "dirt" from the middle of a mowed area, but your gorgeous garden soil sounds awesome! If you've been composting, mulching, it should be "black gold!"

I use some soil from my garden in pots too, and plants seem to like it a lot better than bags of "potting soil." For either choice, I change it about every year or 2, and it was getting way too expensive to keep buying. Bags that say cactus or palm soil are a lot better, but still take a bite out of a plant budget. I try to only use bought soil in really big pots, and a window box, because it does weigh a lot less. If your plant was happy until the roots filled the pot & the soil became old, there's no reason not to repeat with the knowledge that you'll do it again when you notice your plant has slowed its' growth or starts to look less healthy.

Many of my pots are outside more than half of the year, where they can be rained on and none have experienced root rot/overwatering, even with they house succulents.

@Tiffany. I'm grateful for your kind and knowledgeable comments. I must repeat that I don't fill the pot with my garden soil, just maybe one-third, for living nutrition and fiber. I can't afford to put 100% bagged soil into all my plants.

What's your definition of "really big pots"? I'm curious. I will, on Dave's advice, repot my schefflera. I understand that you are not supposed to repot into a much larger container. But I don't know how to define that. And I know that some indoor plants want to be rootbound. What to do, what to do. I love my scheffleras.

I see you are in a hotter climate than me. You certainly don't put your houseplants right into an all-day-sunny spot, do you? I have tried that, and learned to place my sunloving plants under a tree.

Happy to share. I define a really big pot as one that I can't pick up when full.

If you are going to remove the old soil & trim the roots a bit, the size of the new container is irrelevant, beyond practical concerns about being able to move it. The old wives' tale about not switching plants to a significantly bigger pot comes from the use of peaty potting soil that can rot roots because of its' lack of oxygen, and from folks potting-up plants vs. repotting. Potting-up being when an undisturbed root ball is placed into a larger pot surrounded by more soil. I would never pot-up a woody entity, mine are always repotted with old soil removed, roots that are too long to fit back into pot without bending are trimmed. If one is not using a soil of a type that will cause this rot (overwatering,) there is no concern about the pot being too big.

I am glad you mentioned also being under the spell of an another old wives' tale about any plant preferring to be in a rootbound state so we can help put that myth out of its' misery. They are twin myths that are usually found together. No plant likes to be rootbound. What is necessary for plants to stay alive is for their roots to not rot, which can happen so easily in a pot with dense soils, like ground dirt, or bagged mixes of predominantly tiny particles of peat, (or to simply shrivel from simply never getting any water.) Having very little soil around the roots would make the soil dry more quickly, and for even the most dedicated plant-overwaterers to not rot the roots of their plants. This is not ideal, since most non-cactus plants are stressed by dry conditions, it's just a way of coping with soil that has little air in it when moist.

Negative experiences in regard to potting-up, where an undisturbed root ball is placed into a bigger pot with more soil around it, vs. doing a repotting, as described below, can give rise to old wives' tales about plants not liking to be repotted/disturbed. Potting-up a root-bound plant that has roots surrounding the outside root ball often lead to this negative experience because those roots had adapted to accessing oxygen around the outside of the root ball and surrounding them with more dense, soggy-but-airless potting soil will likely lead to suffocation.

The reason bonsai masters are able to keep potted entities alive for hundreds of years is because they care for the roots by trimming them and changing the soil. A plant grows from the roots-up, so if the roots are not healthy, gorgeous foliage will decline &/or no flowers can form. When you unpot a plant and find a pancake of roots at the bottom, chopping that off will give roots a chance to grow normally again for a while and will make removing the old soil easier.

Roots need oxygen & moisture at the same time to function. Just air = shriveling. Just moisture = suffocation & rotting. Either will cause root death and dessicated foliage because the roots have been unable to deliver moisture. Having to let soil dry, as if ones' tropical jungle plant was a cactus, is an unnecessarily stressful coping mechanism for non-desert dwelling plants in soil without enough oxygen for the roots to stay healthy when it is moist and can lead to premature loss of older leaves and in extreme cases, dry shriveled roots/dead plant.

The ability of roots to be able to function properly depends greatly on the soil structure/texture, which can change over time. Potting soil tends to be very dense, mostly peat, with very little air in it. Any kind of organic ingredients decompose into smaller bits over time, and roots fill air spaces over time as they grow through soil. Replacing soil periodically is usually necessary to keep plants healthy because of these reasons. A more porous, chunky, airy soil (like cactus/palm, if one is buying bagged,) can have more air in it even when it is moist because there is space between the particles. When there are tiny particles of any kind in a pot, such as peat, sand, silt, clay, they filter into all of the tiny spaces in a pot, eliminating the air. "Overwatering" is the label and manifestation when roots have suffocated and/or rotted, combo of both. Over time, organic bits decompose into smaller bits, so even the "best" soil, if it has organic components, will need to be replaced when this happens. The speed at which this happens depends on many variables, but on average, about 1-3 years.

You're right about the potential for sunburn damage from a sudden & drastic increase for plants that have been inside. If one wants to acclimate an indoor plant to significant direct sun exposure outside, it needs to be done gradually, to avoid sunburn. Not all plants would benefit from such an adjustment, and the length of time it would take for any particular plant would depend on what kind of plant it is, on the length of ones' outdoor season, and what kind of exposure it had when it was inside. In Z3, your options are much more limited, due to much shorter length of the warm season outside, than where I am. Under a tree sounds fine for your plant!