When is the latest time to sow seeds in spring?
We are often asked to advise on the best time to sow wild flower seed, and what is the latest time in spring you can sow and still expect results?
In practice this is quite difficult to predict as so much depends on the particular pattern of weather that develops each spring. Seeds need both warmth and moisture to germinate and grow. These conditions are most often met during March and April but can vary depending on season, soil type and location.
Early spring sowing is recommended wherever practical. How early you can start sowing will depend on workability of your soil. Light free draining soils are often ready from early March. Cold wet clay soils may not be suitable until April.
Cornfield Annuals do need to be sown by the end of April to have enough growing time to produce a good display of flowers. Annuals sown in early May can sometimes work provided they have ideal growing conditions and get off to a quick start.
Meadow mixtures sown in the open before the end of April are usually successful. In most years there is enough rainfall for seedlings to get well established with good roots ahead of summer droughts.
Later spring/ early summer sowing
Meadow and grassland mixtures are composed of perennial species and can be established at any time of year when there is sufficient moisture and warmth. Late spring and early summer sowing can be successful if the weather is kind, but may carry a higher risk of problems if drought follows.
Sowing of meadow and grassland mixtures can be successful in May or even June if followed by a spell of wet weather. Seed sown in May to July will often establish well in western regions with a wetter climate.
Late spring and summer sowing is however more risky on drought prone sites in drier regions; unless the forecast for rain is particularly promising it may be safer to postpone sowing here until Autumn.
Rolling seedbeds in drier conditions can help improve seedling establishment.
Rolling will firm the seeds into contact with the soil and connect them by capillary action with moisture below the surface. Loose seedbeds by contrast are prone to dry out at the surface depriving surface sown seed of moisture.
Watering is perhaps an option for smaller sites. If you do decide to water make sure you water thoroughly and can keep watering through the dry spell until your seedlings are well established.
Irrigation is necessary for most green roof sowing in spring. The shallow depth of growing media used on most green roofs can only hold a limited amount of water and seedlings on roofs are therefore more likely to experience drought conditions.
Posted on 19 April 2016,