When to plant hyacinths in San Luis: by 24 May

Hyacinth in San Luis: depth, winter cold, pests and pets

Plant hyacinths 10 cm deep, at least 7.5 cm apart (RHS).

In San Luis the average daily temperature stays at 10 °C or lower for about 5 weeks a year (our estimate from ten years of monthly weather). For this bulb Wisconsin Horticulture Extension gives a cold period of 12–15 weeks at about 2–10 °C. That is less than the bulbs need, and without more cold they may not flower properly. Where winters are not cold enough for long enough, LSU AgCenter keeps tulip and hyacinth bulbs in the refrigerator for at least six to eight weeks before planting, and plants them only once the soil has cooled: warm soil can cancel the chilling. Keep fruit out of that refrigerator — ripening fruit gives off ethylene, which harms the flowers (Wisconsin Horticulture Extension).

Flowers get smaller in the years after planting: for full spikes, replace the bulbs or add a few new ones each autumn (RHS).

If squirrels are a problem, protect the bulbs with wire mesh (RHS). Hyacinths are toxic to dogs, cats and horses: intense vomiting and diarrhoea (ASPCA).

Sources: RHS, Wisconsin Horticulture Extension, LSU AgCenter, ASPCA.