Planting black-eyed Susan: planting & care tips

Black-eyed Susan is easy to care for when planted in the right location. It makes a great hanging plant and, with the help of climbing aids, can spruce up many a dreary wall.

Black-eyed Susan (Thunbergia alata) belongs to the genus Thunbergia. It is easy to grow at home, making it a great option for those new to gardening. Keep reading to find out more about sowing and planting black-eyes Susans, which pests to look out for, and how to care for these pollinator-friendly plants. See our overview article on black-eyed Susans for essential information on propagation, winter hardiness and toxicity.

Planting black-eyed Susans

Planting black-eyed Susans does not require extensive know-how. While these plants are not overly picky, where you choose to plant them will determine how abundantly they bloom.

Where to plant

Although black-eyed Susans can tolerate a variety of growing conditions, they will not do as well in waterlogged soils or in cold, windy or rainy locations. Generally speaking, you can plant black-eyed Susans in a garden bed or, using a suitable potting soil, in a pot or container. Thunbergia alata prefers acidic to alkaline, sandy, or clay rich soil, a sunny but airy location, and temperatures around 17 to 20 °C. It can handle dry spells a lot better than being in waterlogged soil, so if this is likely to be an issue, install a drainage system using gravel, expanded clay or clay shards.

Whether in a window box or in a garden bed, south-facing balconies, fences or house walls are ideal places for black-eyed Susans. When choosing a substrate, opt for a humus-rich soil to keep the need to water and fertilise to a minimum. Our Plantura Organic Flower Compost provides the perfect conditions for growing black-eyed Susans and helps to encourage beautiful blooms. Its high compost content means that it retains water well, while the expanded clay, coir pith and wood fibres ensure good drainage which helps to prevent waterlogging. It is also entirely peat-free, making it a more sustainable and environmentally-friendly option.

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Do black-eyed Susans need a climbing aid?

Just like star jasmine, honeysuckles and wisterias, black-eyed Susans are twining climbers. This means they grow upwards by winding their way up a climbing aid or object. To make the most out of this, try planting your black-eyed Susan next to a trellis or some wooden plant stakes. If no climbing aid is available, the plant will creep and grow as more of a groundcover. If your space could do with the addition of a beautiful hanging plant, try planting black black-eyed Susans in a hanging basket or a window box.

Tip: Thunbergia alata twines to the left, so if you place the shoot on a trellis, it is best to place it on the right side of the pole.

Sowing black-eyed Susan seeds

Growing black-eyed Susans from seed is easy. Start by sowing your black-eyed Susan seeds indoors between February and April. To save space and soil, sow them in seed trays. Loosely sow the seeds about 5cm apart in nutrient-poor soil, such as our Plantura Organic Herb & Seedling Compost. Cover with 0.5cm to 1cm of soil, as black-eyed Susan seeds only germinate in darkness. Keep the soil moist, not wet. The seeds should germinate after 14 to 21 days.

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Once your black-eyed Susan seedlings have grown their first pair of true leaves, it’s time to prick them out and pot them on. Maintaining a planting distance of 5cm, place three to five seedlings in a pot with a diameter of at least 35cm filled with nutrient-rich potting soil. Insert the climbing aids into the pot as well. The black-eyed Susans will find the climbing aids independently and twine their way up in an anti-clockwise direction. Based on how vigorous a grower your plant is, you can snip off the shoot tips to encourage bushier growth.

How to plant black-eyed Susans

After the last chance of frost has passed around mid-May, move your black-eyed Susan outside and plant it either directly into the garden bed or into a pot.

Step-by-step instructions on planting black-eyed Susans:

• Choose a sunny, rain-protected, and airy location
• Clear the soil of weeds, stones and roots
• Dig a generous planting hole, at least twice the size of the root ball
• Enrich the excavated soil with nutrient-rich potting compost if necessary
• Install a drainage layer made of gravel at the bottom of the hole if necessary
• Place climbing aids into the soil if you want your black-eyed Susans to twine
• Plant the young plants deep enough into the hole so that the root neck is at the surface of the soil — fill in the planting hole, as needed
• Keep a planting distance of about 50cm
• Press everything down and moisten the substrate, avoid waterlogging

If you want to plant your black-eyed Susan in a container or window box, make sure that the soil is rich in humus. To avoid waterlogging, clay shards or gravel can serve as drainage.

Tip: the pot for a single Thunbergia alata needs to be at least 25cm in diameter and 30cm high. You can grow three plants to five in a pot with a diameter of 35cm. Pots with larger volumes make it easier to care for this beautiful climbing plant and ensure a healthier growth.

Black-eyed Susan care

Black-eyed Susan is a low-maintenance ornamental. There are just a few things to bear in mind to keep it healthy and thriving.

Watering, fertilising and pruning

When watering black-eyed Susans, do not overwater or underwater. Try to find the sweet spot by watering little but often. Furthermore, avoid getting the leaves too wet, as this can cause spots on the foliage and flowers.

To ensure beautiful blooms, fertilise your black-eyed Susans on a weekly basis. Our Plantura Liquid Flower Food has an ideal nutrient ratio for flowering plants such as geraniums (Pelargonium), petunias (Petunia) and black-eyed Susans. As it is a liquid fertiliser, it is easy to apply by simply adding to water, making it particularly suitable for plants in pots, tubs, or balcony boxes.

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Deadhead your black-eyed Susans regularly to help stimulate new flower formation. To promote bushier growth, prune the stems about 3 weeks after planting your black-eyed Susans. Before bringing them indoors for the winter, prune back to about 50cm. See the section on overwintering black-eyed Susan in our overview article for further advice on getting them through the cold months.

Common pests and diseases

Black-eyed Susans are susceptible to root rot and a variety of pests. Keep reading to find out more about some of the most common pests and diseases and how to remedy them.

Spider mites

A couple of tell-tale signs of spider mites include webbing and light dots on the leaves. An infestation can lead to leaves that appear completely white-yellow. Dry, stale air provides an ideal habitat for spider mites. If you find your black-eyed Susans are infested, head over to our article to read up on how to get rid of spider mites.

Aphids

Aphids are small, black pests that usually appear in colonies on the underside of the leaves or on shoots and are therefore easy to recognise. An aphid infestation will result in deformed leaves, sticky or even black spots, and possibly even leaf discolouration due to the transmission of plant viruses. In case of infestation, we recommend taking biological plant protection measures as soon as possible. Neem-oil-based plant protection products are a natural and highly effective way of controlling aphids. Remember to follow the instructions in the enclosed leaflet. Follow the link for further advice on controlling aphids.

Root rot

While root rot is not a pest, it is just as harmful to black-eyed Susans. If your plants are sitting in soil that is too wet, the roots will begin to rot. You can recognise this by wilting leaves and chlorosis, i.e. lightening or yellowing of the leaves. If you are growing black-eyed Susans in pots, take them out of the pot, free them from the wet soil, and repot into new substrate. Refrain from watering for a short time, and then water sparingly. It’s a little more complicated for bed plants. Start by checking the soil conditions, making sure it is airy and loosening it to prevent further waterlogging.

Nutrient deficiency

Yellow leaves on black-eyed Susan’s can also be the result of nutrient deficiency. Remember that Thunbergia alata converts fertiliser into growth quite rapidly, so you can fertilise this climbing plant more generously.

Cold, wet weather

Wet, wintry weather often causes leaf spots and reduced growth. This will resolve itself once the weather improves or can be avoided by placing the plant in a sheltered spot.

Black-eyed Susan not flowering: what to do?

It is normal to be disappointed if your Thunbergia alata is not flowering. Luckily, this is a rare occurrence. Generally speaking, black-eyed Susans will still flower reliably even in low-light conditions, so you can rule this out as a cause. This problem is more likely down to a suboptimal planting location. Instead of planting your black-eyed Susans elsewhere, check the soil is not waterlogged and that the plants are receiving enough nutrients. Once you’ve sorted anything that needs rectifying, your black-eyed Susan should begin flowering once again.