Why Won't My Radish Seeds Germinate?

Radish is generally one of the most reliable and fast-germinating crops in the vegetable garden — under good conditions, seeds are up in three to five days. When they fail to germinate at all, or germination is patchy and sparse, something straightforward is usually to blame. Because radish is genuinely easy to germinate when conditions are right, the problem is almost always simple to identify and fix for the next sowing.

Sown too deep

Radish seeds are small and should be sown no deeper than 1–1.5 cm. Deeper than this and the seed does not have enough food reserves to push the seedling all the way to the surface, particularly in compacted or heavy soil. If you are sowing in drills, make the drill shallow and cover the seeds with no more than 1 cm of fine soil. Press the soil firmly over the seeds to ensure good contact between the seed and the soil moisture below.

Soil too cold or too hot

Radish germinates best between 10–25°C. Below 7°C, germination is very slow or non-existent. Above 30°C, germination rate also drops and the seedling can be damaged by heat. Spring sowings in cold soil will simply wait until temperatures rise — this is not a failure, just patience needed. In very hot summer conditions, sow in the late afternoon so seeds have the cooler evening and night to begin germinating. Most spring radish failures are cold-related; summer failures are often heat-related.

Dry soil after sowing

Seeds must remain moist from the moment they are sown until the seedling emerges. If the soil surface dries out in the days after sowing — particularly in warm, dry, windy conditions — seeds will have begun the germination process but then desiccate before emerging. Water immediately after sowing and keep the surface moist. A thin layer of fine compost or vermiculite over the seed helps retain surface moisture without impeding emergence.

Old seeds with low viability

Radish seeds remain viable for around four to five years under good storage conditions. Beyond this, germination rates drop. If your seeds are old or have been stored in a warm, damp location, test viability by placing ten seeds between damp paper towels and checking for germination after five days. Fewer than seven out of ten sprouting indicates low viability.