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Geranium

Series: Bulls Eye™, Elite™, Maverick™, Pinto™, Multibloom™, Orbit™, Orbit Synchro™, Ringo 2000™

 

1. Soil and pH Needs

Geraniums are very adaptable and will grow in almost any kind of soil. The soil should be open and porous to allow for good water drainage, oxygen penetration, and healthy root growth. A heavy soil will benefit from the incorporation of several inches of peat, compost, or perlite before planting. Do not use manure or vermiculite.  A sandy soil will also be measurably improved by the addition of organic matter. Soil should be amended with fully composted organic matter prior to planting and in the case of clay soils the addition of pea gravel equal to at least 25% of the soil volume will aid in aeration. If adding organic matter, be aware that organic matter that has not been fully composted will tie up nitrogen and sulfur leading to nutrient deficiencies and poor growth.  Soil pH should be mildly acidic 6.5 is ideal and should be tested prior to planting but after adding any amendments. This can be done quite easily with a portable pH tester available for about $100. Mix one part soil with two parts distilled water, stir well and wait thirty minutes, then follow the instructions for using the pH meter. If pH is too low, the addition of lime is warranted. However, the rate will vary depending on how much you need to raise the pH and the type of soil you are dealing with. Clay soils or those with a lot of organic material have a high buffer capacity and require more lime than sandy soils, which have a low buffering capacity. A good soil testing lab can determine the lime requirement index (LRI) of your particular soil and can recommend types and rates of lime to use. The frequency of watering will depend on the type of soil, weather conditions and the amount of mulch. Mulch will not only reduce soil water evaporation but will also reduce splashing of water onto the lower leaves, moderate soil temperatures and reduce weed competition. 

 

2. Fertility

Geraniums are moderate feeders and will not bloom if over-fertilized. An application of a balanced controlled-release fertilizer (CRF) such as 10-10-10 at 2 pounds /100ft2 or 5-10-5 at 4 pounds/100ft2 can be incorporated into the soil at planting. A half-rate application of this dry fertilizer can be applied at mid-season. Water these dry fertilizers into the soil after application. In high pH soils (alkaline soils) additional iron or iron sulfate may be beneficial to reduce chlorosis (yellowing) of the foliage.  Yellow foliage on geraniums may also be caused by a nitrogen deficiency within the plant. Both can be corrected with the proper supplemental fertilizers. 

 

Edge burn due to high soluble salts

 

3. Disease

Geraniums have their share of disease problems. Bacterial leaf spot is caused by the bacterium Xanthomonas pelargonii and is especially prevalent in warm, wet weather where plants are grown in crowded conditions. Disease symptoms include small (pinhead size), circular or irregular, brown, sunken spots on older or lower leaves. Large numbers of spots will occur on a single leaf; these will coalesce killing a large portion of the leaf which will then drop off. As the disease moves through the plant, the lower leaves wilt and yellow. In severe cases, the stem will possess black stem cankers killing the upper portion of the stem. Leaves infected with bacterial leaf spot should be removed as soon as it is noticed. Severely infected plants should be removed, there is no chemical cure for bacterial leaf spot.

Botrytis blossom blight is another common fungal disease of geraniums. It is caused by Botrytis cinerea. Botrytis prefers cool, moist conditions or where plants are watered frequently. Leaves develop zonate, brown leaf lesions which develop a grayish brown mass of fungal spores. The lower leaves will yellow and rot. Flowers may also become infected. They show discolored petals which wilt and fall. Remove affected leaves and flowers. Fungicide sprays, when environmental conditions are favorable, will help reduce levels of this disease. Rust, root rots, stem rot, and leaf spots are other diseases known to infect geraniums. 

  

Bacterial leaf spot on geranium

 

Geranium leaf with Botrytis

 

4. Insects

Insects are usually not a problem for geraniums, as their strong, bitter scent keeps most bugs from bothering them. The most common insect pests are:

Aphids – small green ovate insects usually clustered together at the growing tip of the plants. A good indication of aphids includes small new leaves, small white outer-skin skeletons from the insect (molts), and sticky honeydew on the leaves. The honeydew can sometimes become blackish.

Spider Mites –usually found on the underside of the leaves, very often within their delicate webbing. Spider mites cause speckling damage on the leaves and sometimes cause the leaves to have brown corky areas.

Caterpillars – most caterpillars do their work at night. Look for circular holes in the edges of the leaves, freshly chewed flower stems, dark brown to black excrement left on the surface of the leaves.

Bud Worms – look for small round holes in the new buds or for the small (1/4" –1/2") worms actively feeding on the buds. Wherever you see small moths or butterflies in and around the plants, expect to see bud worms several weeks later.

 

Bud worm damage to flower buds

  

Mite infestation on geranium foliage

  

5. Tips for Success

  • The most important requirement for growing geraniums successfully is a location with at least 6-8 hours sunlight per day. The more shade they receive, the fewer flowers they'll produce. 
  • Whenever feasible, it's a good idea to remove faded flowers, including the portion below each flower where seeds will develop. This practice, called "deadheading," encourages blooming by preventing seed maturation. Although it may not be practical to deadhead masses of geraniums in the garden, it's a must for flowering annuals in containers. Deadheading not only helps prolong blooming, it also keeps plants looking fresh, healthy and well-groomed. 
  • Geraniums are resistant to drought and don't require a lot of water. Take care not to overwater your plants. When you do water, do it early in the day and water only the roots. Wetting the leaves can make them more susceptible to infection with spores from other plants
  • Remove weeds from the plantings that compete with the geraniums for moisture, nutrients and light.

Information provided by Syngenta Flowers