What to Plant in August: Late Summer Microgreens That Actually Work

Quick answer: In August's heat, your best bets for microgreens are heat-tolerant varieties like sunflower, radish, and basil — crops that germinate reliably even when ambient temps climb to 78–82°F. You'll want to prioritize airflow, adjust your watering for faster evaporation, and plan to harvest closer to day 7 instead of day 10 before heat stress causes bolting. Skip cool-weather crops and lean into the season's strengths instead.

August in Milton, Georgia hits around 88–92°F most days, and the humidity tends to hover in the 70–80% range — not exactly ideal conditions for every crop, but some microgreens barely notice.

If you're trying to figure out what to plant in August for late summer microgreens, the short answer is: stick to heat-tolerant varieties, keep airflow high, and skip anything that wants cooler temps to germinate cleanly. The longer answer is below.

Why Late Summer Growing Is Different

Most microgreens germinate best between 65°F and 75°F. In August, if you're growing indoors without strong climate control, your trays might be sitting in 78–82°F ambient temps. That's not a disaster, but it does change a few things.

Germination speeds up. Moisture evaporates faster. And mold risk goes up, especially for varieties with fuzzy seed coats like sunflower. You'll need to adjust your watering and blackout timing accordingly.

The other thing August does is compress your growing windows. Heat-stressed microgreens can bolt (shoot upward and start to go bitter) faster than they would in cooler months, so you're harvesting on a tighter schedule. For most varieties, that means checking trays at day 7 rather than day 10.

Varieties Worth Planting in August

Sunflower

Sunflower microgreens are one of the more forgiving warm-weather crops. They like the heat, they germinate reliably in 2–3 days at summer temps, and they're typically ready to harvest around day 8–10. The main risk is mold under the seed hull — sunflower seeds have a thick outer shell that stays wet. Soak seeds for 8–12 hours before planting, and don't overwater during blackout.

Seed density matters here. A 10x20 tray takes about 2–2.5 oz of black oil sunflower seed per layer (one layer deep, no stacking). Go heavier than that and you'll get poor airflow and more mold problems.

Radish

Radish germinates fast at almost any temperature — you'll usually see sprouts in 24–36 hours in August. It's one of the easiest late-summer crops because of that speed. The window from seed to harvest is short (5–7 days), which means less time for heat to cause problems.

Red arrow and daikon are both solid choices. Red arrow tends to have more consistent germination from seed lot to seed lot, which matters if you're buying in bulk.

Pea Shoots

This one surprises people. Pea shoots are typically thought of as a cool-weather crop, and in outdoor gardens, they are. But indoors, with good airflow and temps kept below 80°F (even a single window AC unit helps), they do fine in August. They take a bit longer — around 10–14 days to a harvestable size — and they're thirsty, so bottom watering is better than top watering in humid conditions.

Use a whole pea variety, not split peas from the grocery store. Speckled peas or Austrian winter peas both germinate well and have a cleaner flavor than some of the generic soup pea mixes.

Amaranth

Amaranth is genuinely a warm-weather microgreen. It wants heat to germinate — below 70°F and you'll get spotty results. In August in North Atlanta, it's in its element. The seeds are tiny (you'll use about 10–12g per 10x20 tray), and they need light to germinate, so you skip the blackout phase entirely. Just mist and keep them under lights from day one.

The tradeoff: amaranth has a longer harvest window (12–16 days) and the yields are lower by weight than something like sunflower or peas. It's worth growing for flavor and color variety, but don't expect a heavy harvest.

What to Skip in August

Broccoli and Brassicas Generally

Broccoli microgreens germinate best around 65–70°F. You can get them to work in August, but you'll often see uneven germination, leggy growth, and a shorter post-harvest shelf life because the heat stresses the plants. If broccoli is important to your rotation (and it's worth growing for its sulforaphane content — multiple studies have measured meaningful concentrations in the sprout stage), wait until September when night temps start dropping.

Cabbage and kohlrabi have the same issue. Save them for fall.

Cilantro

Cilantro is slow in any season. In August heat, it gets slower and more prone to damping off. It needs a nick in the seed coat (the seeds are actually two seeds fused together — called a schizocarp) to germinate well, and even then you're looking at 10–14 days just to germinate. The humidity in a Georgia August makes that stretch risky. This is a September or October crop.

Basil

Basil microgreens are finicky regardless of season. The seeds are mucilaginous — they form a gel coating when wet — which makes them prone to mold if airflow isn't near-perfect. In summer humidity, that's a hard combination to manage without a climate-controlled space. Not impossible, but a lot of growers lose their first few trays before getting the technique right.

Practical Adjustments for August Growing

A few things that actually make a difference in late summer:

Bottom watering keeps the canopy drier and reduces mold risk significantly. If you're top-watering in August, you're working harder than you need to.

Cut your blackout time by 12–24 hours compared to what you'd do in cooler months. Seeds germinate faster in heat, and leaving them in blackout longer than necessary builds up excess moisture.

Fan placement matters. Even a small oscillating fan pointed at your trays (not directly blasting, just circulating air in the room) helps dry the canopy between waterings.

If you're growing in a garage or shed without climate control, morning is your best harvest window — before the heat of the day wilts the greens. Microgreens cut in the afternoon in August heat don't store as well.

A Note on Sourcing Seeds for Summer Crops

Seed quality affects germination more than most new growers expect. For black oil sunflower specifically, look for seeds sold as food-grade or sprouting-grade rather than bird feed. Bird feed sunflower sometimes has lower germination rates and can carry more surface contamination.

For amaranth, most retail seed sources sell it in tiny packets at high prices. If you're planting more than a tray or two, look for bulk vegetable amaranth seed from microgreen-specific suppliers — it's significantly cheaper per ounce and the germination rates tend to be more consistent.

The Milton Farmers Market Window

If you're growing microgreens to sell or share locally, August is actually a decent time to start building a late-summer to early-fall supply. The Milton Farmers Market runs through the fall, and the transition from August to September is when some vendors drop out and buyers are still showing up. Sunflower and pea shoots tend to move well because they're recognizable to people who've never bought microgreens before.

Start your August trays now and you'll have product ready right as September weekend markets hit their stride.

New to microgreens and want the basics before diving into seasonal growing? The Microgreens 101 guide covers germination, trays, and your first harvest from the ground up.

Other articles from the farm

1. Microgreens 101: Everything You Need to Know
2. Explore All Microgreen Varieties (Plant Database)
3. Recipe: Sunflower Microgreen Salad
4. Recipe: Microgreen Pesto

What Most August Microgreens Guides Get Wrong

Most advice you'll find online about summer microgreens is written for growers in temperate climates — think Oregon or the Pacific Northwest — where August highs might hit 78°F on a hot day. That's a very different situation than growing in Georgia, Texas, or Florida, where your garage or spare bedroom might be sitting at 82°F with the AC running.

The biggest mistake: treating heat as a binary problem. Either it's "too hot to grow" or it's fine. In reality, heat affects different parts of the growth cycle differently, and most guides don't break that down.

Germination, blackout, and the light phase each respond to heat in their own ways:

• Germination actually speeds up with heat for most varieties. This isn't a problem — it's just something to account for. Check your trays 12 hours earlier than you normally would.
• Blackout phase is where heat creates real risk. Covered trays trap humidity and warmth, which is exactly the environment where damping off and mold get started. Shorter blackout windows — sometimes 24–36 hours instead of 48–72 — help significantly.
• Light phase is where bolting becomes a concern. Under grow lights in a warm room, some crops will stretch and turn bitter faster than their typical harvest window suggests. This is especially true for mustard, amaranth, and anything in the brassica family.

The other thing most guides skip: seed source matters more in summer than in cooler months. Old seed with lower germination rates will leave you with patchy trays and more exposed, damp growing medium — which means more mold risk. August isn't the time to use up the seed lot you've had sitting around since last fall.

Troubleshooting Common August Growing Problems

Even with the right varieties, late summer growing throws specific problems at you. Here's what to look for and what to do about it.

Leggy, Pale Growth

If your microgreens are stretching upward and look washed out or thin-stemmed, they're not getting enough light relative to how fast they're growing. Heat accelerates growth rate, but your light intensity stays the same. The fix is simple: move trays closer to your grow lights, or increase your photoperiod by an hour or two. For most setups, 14–16 hours of light per day works well in summer. Don't assume the settings that worked in April will carry through August.

Mold on the Soil Surface

White fuzzy growth on your growing medium usually means one of three things: overwatering, poor airflow, or blackout that went too long. In August, all three risks go up at the same time.

If you see surface mold, don't panic and don't add more water. Pull the tray out of blackout early, get a small fan blowing across the surface at low speed, and let the top layer dry slightly before the next watering. Surface mold that hasn't reached the stems yet usually won't kill the crop — but it's a signal to adjust your setup before the next tray goes in.

For recurring mold problems, look at your watering method. Bottom watering — pouring water into the tray beneath your growing tray and letting it wick up — keeps the surface drier and reduces mold significantly compared to top-spraying during the germination phase.

Uneven Germination

Hot spots in your growing space cause this. If one corner of a tray germinates two days ahead of another, you've got a temperature gradient happening — often from a nearby window, a vent blowing warm air, or the edge of a grow light that runs hotter. Rotate trays 180 degrees at the 24-hour mark during blackout to even things out. If it keeps happening, a cheap infrared thermometer will help you find the hot spots in your setup.

Yellowing After Harvest Window

If you're harvesting at your usual day 10 and finding yellowed or bitter stems, you've waited too long. In summer, some crops are best cut at day 6 or 7. Radish especially will turn sharp and fibrous if you let it go past its prime in the heat. Start tasting at day 5 for fast growers. Flavor — not just height — is your best harvest indicator in August.

Frequently Asked Questions About Summer Microgreens

Can I grow microgreens outside in August?

Technically yes, but you'll be fighting direct sun, rain, insects, and temperature swings that are hard to manage. Shade cloth (30–50% block) helps, and a covered porch with good airflow can work for tough varieties like sunflower and radish. That said, indoor growing gives you far more control, and control matters more in August than any other month. If outdoor growing is your only option, stick to radish — it's the most forgiving of variable conditions.

Do I need to run the AC to grow microgreens in summer?

Not necessarily. Consistent temps below 80°F are ideal, but many varieties will grow at 82–84°F if you adjust your process. The bigger concern is humidity. High heat plus high humidity is the real problem. A small window unit — even a 5,000 BTU unit — can drop both temp and humidity enough to make a meaningful difference in mold risk. If that's not an option, a dehumidifier running in the same room will help almost as much.

How do I store harvested microgreens when it's hot?

Refrigerate immediately after harvest and after any rinsing. Don't leave harvested greens sitting at room temperature to dry — spin them dry and get them into a sealed container in the fridge within 20–30 minutes of cutting. In summer, shelf life after harvest drops from 7–10 days to closer to 5–7 days, so plan your harvest timing around when you actually need them.

Is basil worth growing as a microgreen in August?

Yes, and August is actually one of the better months for it. Basil germinates slowly — usually 5–7 days — but it loves heat and won't struggle with the same mold issues that affect other varieties, because its seeds are planted at lower density. Expect a 16–18 day grow time. Don't rush it. The flavor at harvest is noticeably better than what you get from basil grown in cooler, slower conditions.