Spinach is one of the fastest successes in the vegetable garden. From sowing to harvest in 4 to 6 weeks. Possible twice a year — in spring and autumn. And if it works — dark green, juicy leaves that taste and smell like real spinach — then you understand why Popeye was never without it.
If it doesn't work — pale leaves, bolting in the middle of the growing phase, downy mildew on the underside of the leaves — then it's usually due to three things: wrong timing, wrong soil, too little water.
Here is the complete guide.
When to plant — timing is everything
Spinach is a long-day plant (a plant that responds to longer days by beginning to flower). As soon as the day length exceeds 10 to 14 hours, it begins to bolt — the stem stretches, the plant begins to flower, and the leaves become bitter and inedible.
This means: growing spinach in midsummer almost never works. The days are too long — it bolts before you can harvest it.
The two perfect sowing windows:
Spring — February to April. Outdoors from March, in a greenhouse or under foil as early as February. The short spring days and cool temperatures are ideal. Harvest March to May before the long summer days trigger bolting.
Autumn — August to September. The days get shorter, and temperatures drop. Spinach is hardy and easily survives light frost. Autumn spinach also has an important advantage: it has less oxalic acid (an organic acid that occurs naturally in spinach) than spring spinach — oxalic acid concentrations decrease in the autumn months.
Tip for latecomers: Buy mildew-resistant and late-flowering hybrid varieties — they are significantly more tolerant of longer days. Labeled as "bolting resistant" in specialist shops.
What soil does spinach need?
Spinach is a heavy feeder (a plant that needs a lot of nutrients for its rapid growth) — it needs a lot in a short time.
pH value: 6.5 to 7.5 — slightly acidic to neutral. In soil that is too acidic, spinach hardly absorbs any iron and magnesium — the leaves become pale despite fertilization.
Structure: Loose, rich in humus, well-aerated. All leafy vegetables dislike compacted soils — spinach especially.
Moisture: Evenly moist — but no waterlogging (standing water in the soil that damages roots). Drought stress triggers bolting.
Crop rotation (the sequence of different crops in the same area): Do not plant spinach after spinach, chard or beets — at least 3 years' break. Downy mildew spores can survive in the soil for up to 2 years.
The most common diseases — and what's really behind them
Downy Mildew — the most common enemy
Downy mildew is a serious fungal disease that can severely damage spinach crops. First, irregular yellowish spots appear on the upper side of the leaves. A grayish fungal mycelium forms on the undersides of the leaves in the affected areas. The fungus develops primarily in humid weather at temperatures of 8 to 18 degrees Celsius.
What's behind it: Downy mildew loves stressed plants with thin cell walls and high leaf wetness. A spinach plant well supplied with calcium has denser, more stable cell walls — fewer entry points for fungal spores. The zeolite film from Grünkraft Zeolith Pur on the leaf surface prevents the formation of the moisture film that fungal spores need for germination.
Remove affected leaves immediately — affected plant material can transmit the disease to the subsequent crop, and the oospores (resting spores of the fungus) that form can survive in the soil for a long time.
Leaf Spot Disease — Septoria and Alternaria
Dry brown spots with a red margin — that's Septoria. Yellowish to brown spots in wet weather — that's Alternaria. Both are fungal pathogens that prefer weakened plants. Cut off affected leaves and dispose of them in household waste — never compost them.
Bolting — when spinach flees
Bolting is not a pest or disease — it is the natural reaction to overly long days or drought stress. As soon as spinach bolts, it is inedible — the leaves become bitter.
What helps: Correct sowing time, consistent moisture, bolt-resistant varieties. And a well-nourished plant with a high Brix value (the measured value for nutrient density in the plant sap) bolts later than a stressed one.
Snails
The classic garden enemy — especially for young plants. Organic snail traps or snail fences protect the young plants in the first few weeks after sowing.
Beet Fly
The beet fly lays its eggs on the underside of the leaves. The hatched larvae eat their way through the leaves. The zeolite film from Grünkraft Zeolith Pur acts as a physical repellent against egg laying.
The complete program for nutrient-rich spinach
Step 1 — Prepare the soil: BODENKRAFT Carbonate of Lime + BODENKRAFT PUR
Timing: 2 to 3 weeks before sowing.
BODENKRAFT Carbonate of Lime stabilizes the pH value in the optimal range for spinach. Tribomechanically activated (charged by a high-speed process) with over 90 percent soil reactivity (effectiveness in the soil) — four times more effective than conventional broadcast lime.
BODENKRAFT PUR Zeolith buffers the moisture in the soil evenly — the most important factor against bolting in drought stress. At the same time, it improves nutrient availability in the root area.
In the garden: Lightly rake in a handful of BODENKRAFT Carbonate of Lime and a handful of BODENKRAFT PUR per square meter.
Step 2 — Activate soil life: AM+PLUS Microorganisms
Timing: At sowing and then every 3 to 4 weeks.
AM+PLUS activates the soil microbiome (the community of beneficial microorganisms in the soil) and makes nitrogen, iron, and magnesium available to plants — exactly the minerals spinach needs for intense chlorophyll-green.
Application: Into the irrigation water with the first watering after sowing, then every 3 to 4 weeks.
Step 3 — Sowing correctly
Sow spinach seeds 2 cm deep, spacing 5 x 25 cm — enough space for the plants to get light and not grow too close together. Too dense planting promotes downy mildew due to lack of air circulation (air flow between the plants).
Keep evenly moist until germination — spinach germinates at 5 to 20 degrees Celsius, optimally at 10 to 15 degrees. For spring sowing, protect under fleece or foil until the soil is warm enough.
Step 4 — Foliar fertilization: Grünkraft Calcium from the 2-3 leaf stage
Timing: As soon as the first true leaves appear — start early!
Spinach, as a fast-growing plant, reacts particularly strongly to CO₂ supply via the leaf. Grünkraft Calcium delivers CO₂ directly into the leaf tissue — the photosynthesis machine runs at full speed. The result is visible and measurable:
Darker, more intense green — more chlorophyll (the green pigment where photosynthesis takes place) due to more intense photosynthetic activity.
More lutein, zeaxanthin, and kaempferol — secondary plant compounds (protective and active substances that the plant itself produces) that are produced with excess energy.
More stable cell walls due to calcium — fewer entry points for downy mildew.
Earlier harvest readiness — in field trials with leafy vegetables from Colombia, lettuce was harvested 7 days earlier than the control group.
First application at 2-3 leaf stage: 5g per 1 liter of water. From the second application every 10-14 days: 20-30g per 1 liter of water. Spraying time: Early morning when the stomata (leaf pores) are open — never in midday heat.
Step 5 — Protective film: Grünkraft Zeolith Pur
Timing: In parallel with Grünkraft Calcium — especially in humid, cool weather when downy mildew threatens.
The fine silicate film (mineral film made of zeolite) on the leaf surface prevents the formation of the moisture film that fungal spores need for germination. At the same time, it acts physically against aphids and beet flies.
Renew immediately after rain.
Harvest — how and when
Spinach can be harvested in two ways:
Leaf by leaf — cut off the outer leaves individually. The plant regrows and provides multiple harvests. Ideal for the garden.
Whole plant — cut off just above the ground. Faster, simpler, for larger quantities.
Spinach is ready for harvest when the leaves have reached their full size — but before the plant begins to bolt. This is the crucial window.
Tip: Harvest in the morning when the leaves are still cool and fresh. Freshly harvested spinach quickly loses vitamins in heat — cool or process immediately.
Spinach in pots and on the balcony
Spinach also works very well in pots — at least 20 to 30 cm deep, so that the roots have enough space.
Substrate: normal vegetable soil mixed with a handful of BODENKRAFT Zeolith PUR powder and GARDENKRAFT Bio Zeolith Pellets. This buffers moisture and keeps the soil loose.
On the balcony: Spinach needs consistent moisture. On hot summer days, a pot in the sun can dry out within a few hours — this immediately triggers bolting. Water in the morning, add BODENKRAFT PLUS Water Storage Pellets to the substrate, and choose semi-shady locations if possible.
The complete program at a glance
| Phase | Measure | Product | Timing |
|---|---|---|---|
| 2-3 weeks before sowing | Prepare soil | BODENKRAFT Carbonate of Lime + BODENKRAFT PUR | Once |
| At sowing | Activate soil life | AM+PLUS in irrigation water | With first watering |
| 2-3 leaf stage | First foliar fertilization | Grünkraft Calcium 5g/l | Start early |
| Growth phase | Foliar fertilization + protection | Grünkraft Calcium 20-30g/l + Zeolith Pur | Every 10-14 days |
| In case of mildew risk | Renew protective film | Grünkraft Zeolith Pur | Immediately after rain |
| Entire season | Maintain soil life | AM+PLUS | Every 3-4 weeks |
What's really in spinach — folate, lutein, chlorophyll and the Popeye myth — in the Spinach Nutrients article.
How foliar fertilization boosts photosynthesis and secondary plant compounds — in the Photosynthesis article.
Measure spinach Brix value yourself — in the Brix article with instructions.
All products for the garden in our Garden Collection.
Sources: Hortipendium, Spinach Plant Protection | Kiepenkerl, Spinach Cultivation and Care | Plantura, Spinach Profile and Winter Hardiness | Gartenrat.de, Spinach Cultivation | Garteln.info, Diseases and Measures for Spinach | UMID Colombia S.A.S., Field Trials Leafy Vegetables Colombia 2017-2018
