When to Harvest Sweetcorn
Sweetcorn has a short window of peak sweetness, so inspect cobs frequently once the silks darken. In a good UK summer, harvest often begins from late July or August and continues into September. The best test is a plump kernel that releases milky sap when gently squeezed.
Start watching cobs about three weeks after the silky threads first appear at their tips. At first, these silks are pale and fresh; as the cob ripens they turn brown, dry and slightly sticky. This is your signal to inspect rather than harvest automatically. Feel the cob through its husk: it should be well filled, broad through the middle and have a rounded, not pointed, end. Check several plants because cobs mature at different speeds. Sunny southern gardens can begin earlier than cooler northern, exposed or Scottish plots, and a delayed spring can shift the whole harvest later.
Use the kernel test for the most accurate answer. Peel back only a small section of husk near the middle of one cob and press a kernel with a fingernail. Clear liquid means it is unripe, creamy milky juice means it is ready, and thick or doughy contents mean it is past its sweetest stage. Fold the husk back after testing if the cob needs more time. Do not remove every wrapper leaf, as this lets in pests and dries the kernels. Test another cob rather than repeatedly damaging the same one. Once one cob is ready, inspect the patch every one or two days.
Pick sweetcorn as close to eating as possible, ideally immediately before cooking. Sugars begin converting after harvest, so even excellent cobs lose their finest flavour if left warm on a kitchen worktop. To harvest, hold the stalk firmly, grasp the cob and pull it downwards with a quick twisting movement. The cob should snap away cleanly. Leave the plant standing until all cobs have been picked, as later cobs may still be developing. Gather early in the morning or evening if you can, when cobs are cool and less likely to dry out during the walk back from the allotment.
Sweetcorn plants often produce one main cob and sometimes a smaller second cob. Do not assume the second cob is ready when the first is picked. It may need another week or may never fill properly in a cool season. If a cob feels thin or has a very pointed tip, leave it a little longer before testing. Poor pollination creates gaps in the rows of kernels, but does not necessarily make the cob unusable. Cut away sparse areas during preparation. Growing sweetcorn in a block rather than a single row next year helps wind pollination and leads to fuller cobs.
If you cannot eat the crop immediately, cool cobs quickly and keep them in their husks in the refrigerator for a short period. For longer storage, blanch kernels briefly, cool them rapidly, dry well and freeze in labelled containers. Whole cobs can also be blanched and frozen, although kernels are easier to portion. Do not leave picked cobs in a hot greenhouse, car boot or sunlit room. Remove husks and silks only just before cooking or freezing. Compost the husks and stripped cobs, or add them gradually to a compost bin with softer green waste.
For a longer harvest, sow an early, mid-season and later variety where your local season allows, rather than sowing everything on one day. Start seeds in module trays of peat-free multipurpose compost in April or May, then plant out after the last spring frost once plants are hardened off. A sheltered sunny site is valuable, especially outside the south. Water deeply during dry spells as cobs form, and mulch with garden compost to retain moisture. Avoid planting a single short row, which pollinates poorly. A compact block allows pollen from tassels to reach silks across the group.
Frequently asked questions
Why are the kernels watery rather than milky?
Watery, clear sap shows that the cob is not ready. Re-cover the exposed kernels as best you can and wait two or three days before checking another cob. Warm sunny weather can speed ripening, while cool or cloudy conditions slow it. Keep plants watered during dry spells while cobs fill.
Can I harvest sweetcorn after the silks turn brown?
Yes, brown silks are the usual first sign that harvest is near, not proof that every cob is ready. Feel for a full cob and test one kernel for milky sap. Depending on the weather, the correct picking point may be a few days before or after the silks become fully brown.
Why are some rows of kernels missing?
Missing kernels usually result from incomplete pollination, often during wet, still or very hot weather. The cob is still suitable to eat if kernels are otherwise plump and milky. Next year, grow plants in a block, not a line, and gently shake the stems at flowering time to help distribute pollen.
General guidance for UK home gardens and allotments. Conditions vary by region, soil and season; the RHS or a local garden centre can give site-specific advice. Page updated 19 Sep 2026.