Sometimes. The gains you read about sit right next to trials where nothing changed at all. Work on biochar plant growth splits into two piles. Some crops gain, and others show no measurable change or even grow worse in the first year. So the real question is not whether the stuff works. It is whether it works in your soil at your pH, and that answer changes from one garden to the next.
The sandy plot outside my kitchen window went pale green three weeks after I dug in a fresh batch of wood biochar. High-carbon feedstock does that. Soil microbes go after the easily degradable carbon fraction and tie up nitrogen while they work, so the crop pays for it that first year. I checked on that pale patch from the sink every morning until August.
Biochar feeds almost nothing on its own. It is alkaline and porous with next to no nutrient content, so any gain has to come from what it does to the soil around it. Two things do that work. The pore structure holds water, and one trial measured 67.17% water retention with biochar against 55.5% without it after 20 days. The second is cation exchange, which means the char grips nutrients that sit in the ground already and lets them go a bit at a time.
That same grip is why char makes fertilizer go further. You are not adding food for the plant when you add biochar. You are giving the food you already apply somewhere to stay put, and most biochar soil benefits trace back to those two effects. It is also why the same bag does nothing in ground that already holds water and nutrients fine.
Trial numbers get quoted a lot, and each one comes from one crop in one type of soil. Utah State University Extension reports an Oregon dryland wheat system where 10 tons per acre (22 t/ha) raised soil pH. Yield went up by almost 30%. Other trials ran in salty and acidic ground with different feedstocks and much lower rates.
Read that table as four separate fields, not as an average you can expect. Biochar crop yield in a bed you dug yourself has no trial standing behind it. Neutral and negative results are documented too, so any honest summary has to name them. That is why the answer up top was sometimes. The effects are not universal, and they have to be matched to whatever you are trying to fix.
Mix fresh biochar into compost and let it sit before it goes in the ground. Raw char with a heavy carbon load pulls nitrogen out of your soil instead of holding it there for the crop.
Test your soil pH before you spend a dollar. Biochar runs alkaline, so it helps sour ground and works against you in soil that already sits high. The trials above ran in saline and acidic soil, and the research does not establish which soil type responds most. Nobody has sorted that out yet.
Buy one small bag, charge it in compost, and work it into a single bed while its neighbor gets nothing. One season of that tells you more about biochar plant growth in your own ground than any published average. It is an informal look and not a trial, so read whatever happens as one bed's answer rather than a verdict on the material.
Read the full article: Biochar: What It Does and When It Fails
