Grow Three Plants Outdoors – Part 6: Preparing for Flowering

After the summer solstice on 21 July, the nights begin to grow longer. At first this happens slowly, but during August the days become shorter at an ever-increasing rate. This means only one thing – flowering time is approaching! In today’s instalment of our outdoor series, we will focus on the transition period between the vegetative phase and flowering and learn how to prepare plants so that they produce a plentiful harvest in the second half of summer.

In the previous instalment, we covered the most common pests that can threaten your garden. However, we hope that you have avoided all such problems and that your plants are now in full strength and ready to flower. It will still be several weeks before the first flowers begin to appear, but you can gradually start noticing small changes.

Signs of flowering

During the vegetative phase, plants invest energy in growth and the formation of new leaves. As the time to flower approaches, however, the way they grow also begins to change. A well-known phenomenon is a short period of accelerated growth immediately before flowering begins. This so-called “stretch” is particularly noticeable when growing indoors, where the length of day and night changes immediately. During outdoor cultivation, when the photoperiod changes gradually, this phenomenon is less pronounced, but you should still expect your plants to grow considerably taller before the first buds appear.

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Just before the buds appear, the shape of the growing tips also changes. They become denser and develop more new light-green shoots. The first flower buds will soon grow in these places, more precisely the stigmas, which look like white hairs. Flowers grow at the growing tips and at every leaf node.

Watch out for male plants: Most growers now cultivate plants from feminised seeds, which produce only female plants, so they do not have to worry about males pollinating their crop. However, if you are growing from regular seeds, bear in mind that males begin flowering slightly earlier than females. You can prevent the female flowers from being pollinated by removing the males from the garden before they release pollen. Male flowers consist of five petals which, when they open, reveal five stamens that release pollen. Male flowers grow on short stems in the same places as female flowers.

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The last opportunity to shape your plants

When plants are young, they have flexible green stems that can be bent easily. As they age, however, the stems become woody and the risk of them cracking when bent increases. If you are tying plants to nets or bending them to fit inside a greenhouse, it is a good idea to do as much shaping as possible by the end of July.

Pinching out the growing tips to encourage branching can theoretically still be carried out one to two weeks before the first buds appear. However, if you do not know exactly when your cultivar will begin flowering, it is safer to make the final pruning no later than the second half of July.

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Fertilising for flowering

In general, plants in vegetative growth require larger amounts of nitrogen (N), which they use to form new green parts. As they transition into flowering, their consumption of phosphorus (P) and potassium (K) increases. The method and frequency of fertilising depend on your growing method.

In beds the soil should theoretically contain enough nutrients for healthy plant development. This is, of course, provided that the beds are properly cared for and nutrients are regularly replenished through mulching and the addition of compost and other organic inputs. During flowering, however, you can support the plants with an extra dose of phosphorus and potassium, which will help with flower formation. When growing in beds, it is best to choose organic fertilisers for this purpose and work them into the soil before the first buds appear. Liquid mineral fertilisers do supply nutrients to plants quickly, but they act for a short time, damage the soil microbiome and are washed out by rain. Therefore, when growing in open ground, they should only be used when necessary.

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When growing in pots the soil will eventually become depleted and the plants will need to be fertilised. The choice of fertiliser is up to you. You can use mineral or organic fertilisers intended for soil, either liquid or slow-release. However, be consistent: if you started growing with mineral fertilisers, do not switch to organic fertilisers halfway through the process. They work on a different principle, and the plants may not survive the change in nutrition. Most fertiliser manufacturers divide their feeding programmes according to growth stages, so all you need to do is follow the table.

That is all for today. In the next instalment of the Grow three plants outdoors series, we will focus on flowering itself and how to protect the crop from adverse weather and mould.