Authored by:
Mauricio Avila
This fall is for testing and calibrating. 2027’s garden will thank you.
September brings a temptation to declare victory. The tomatoes are coming in, the peppers are finally ripening, and the hard work of summer feels like it’s paying off. But September is also one of the most important months for soil health – not because of what’s happening right now, but because of what you set in motion for next year. A few hours of attention to your soil this month can make an enormous difference when you plant again in spring.
What you need to pay attention to right now:
Before adding amendments or making changes, look at what your soil is telling you. If you see cracking or crusting on the surface, your soil needs more organic matter. Cracking soils tend to be low in the biological activity and exhibit poor structure – conditions that make water penetration, root growth, and nutrient exchange all harder.
One of the simplest and most revealing things you can do this month is a basic pH test. Inexpensive pH strips – a box of 50 costs just a few dollars – can tell you a great deal. Make a soil slurry using a small amount of soil and distilled water (or bottled water but never tap water). Then, dip the strip into the slurry, wait for the recommended time, and compare the color of the strip to the pH color chart from the package. If your pH is high (above 7.0, meaning alkaline), applying elemental sulfur like Earth Science Fast Acting Sulfur now will begin acidifying your soil over the fall and winter, arriving at a more plant-friendly pH level by spring. If your pH is low (below 5.5, meaning acidic), applying a calcitic lime like Earth Science Fast Acting Lime now will have months to neutralize the acidity before you plant again in spring.
The timing here matters. Sulfur and lime both work slowly – neither will correct your soil pH in a week. Applied in the fall, they have September, October, and November to do their work before hard frost, giving you a genuinely improved soil in the spring. Applied in spring just before planting, it is too late for them to help your soil and crops in that growing season.
Many gardeners send soil samples to a lab in late October or November, after the crops come out. That’s understandable – it’s a natural end-of-season checkpoint. But it may not be giving you the most useful information. The soil in late fall, after crops have been removed and microbial activity has slowed, looks quite different from the soil in July, when the garden is at peak activity and plants are drawing heavily on nutrients.
If you can, collect soil samples between July and September – the period when your soil is most biologically active and when nutrient cycling is happening most intensively. A September sample, taken while crops are still in the ground, gives you a snapshot of how your soil is actually performing during the growing season, which is exactly what you want to know. That information, combined with lab recommendations, sets you up well for spring amendments and fertilization.
September is an excellent time to add earthworm castings and other forms of organic matter. Earthworm castings improve soil structure, support microbial life, and release nutrients slowly as they decompose over the fall. Spread them on the surface – they will work their way into the soil on their own throughout the fall, and you can mix them in lightly when you turn the bed in spring.
One product you must save for spring: fertilizers with significant nitrogen content. If you apply nitrogen fertilizer now, with no crops actively growing to take it up, that nitrogen is likely to be flushed out of the soil by fall rains and spring snowmelt. You lose the investment and gain nothing. Wait until spring when roots are actively growing and the crops can absorb the nitrogen and use it for plant growth and fruit development while minimizing losses into the environment.
If your soil looks cracked or compacted, Fast Acting Gypsum is a good fall addition. Gypsum – calcium sulfate – helps break apart compacted soil, improves drainage, and can help counteract sodium buildup in areas with salinity (high salt water or soil) and/or sodicity (high sodium water or soil). Unlike lime, gypsum does not significantly change pH, so it is safe to use in most soils without needing to complete a pH test beforehand.
One piece of advice that surprises many gardeners: In September, stop letting your tomato and pepper plants put energy into new flowers and young fruit. Any flower that sets now has almost no chance of producing a ripe fruit before frost. Meanwhile, the plant is burning energy that could be going into finishing the fruit already on the vine. So, do yourself and many of your plants a favor and prune away!
Cut off all the flower buds and any very young fruit on your tomatoes and peppers. Let the plant concentrate on what’s already there. The tomatoes you harvest in October – from fruit that was already well-developed in September – will taste as good as anything you picked in August. The ones that the plant is still trying to ripen from scratch will not.
If you have a bed that will be empty for the fall, consider seeding it with a cover crop – clover is a good, accessible option. Sow the seed now, and it will germinate, establish, and then mostly die back over the winter. In the process, it protects the soil surface from erosion and compaction, adds organic matter as it decomposes, and – in the case of legumes like clover – fixes atmospheric nitrogen into the soil for next season’s crops to use.
A cover crop is not just a placeholder. It is an active investment in soil biology that will feed your plants next year. The cost is a few dollars of seed and an hour of work. The return is measurable.
One final thought on pH that applies year-round but is especially worth considering as you plan for fall amendments: if your household has hard water and you rely on tap water for irrigation, your soil pH is probably trending alkaline. Hard water contains dissolved calcium and magnesium carbonates that raise pH over time. If more than half your garden’s irrigation comes from a tap rather than rainfall, applying Fast Acting Sulfur this fall is likely to be one of the highest-impact things you can do for next year’s garden.
Over time, this can contribute to nutrient deficiencies. Leaves that are yellow with green veins or take on a yellowish to whiteish hue are common signs of zinc and iron deficiencies caused by high pH. Addressing the pH now can help prevent these deficiencies next season and improve your harvest quantity and quality, resulting in juicier, sweeter vegetables and fruits.
September asks for a different kind of attention than the rest of the growing season. It is quieter, more reflective – a chance to look at what the season revealed about your soil and set things right before winter.
The work you do now, mostly invisible and unhurried, is what makes April feel easy.
