Growing geraniums as annual flowers in Minnesota

Geraniums grow well in garden beds and containers. They can be planted after any chance of frost in your area has passed and when the soil temperature reaches 60°F. Geraniums require the following growing conditions: 

• Full sun
  • Minimum 8 hours of sun daily.
  • Less sun means fewer flowers.
• Well-drained soil
  • Allows for good water drainage, oxygen penetration and healthy root growth.
  • If you have clay soil or sandy soil, incorporate several inches of peat or compost before planting.
    • Improves drainage in clay soil.
    • Improves moisture in sandy soil.
  • Do not use manure or vermiculite as they can hold too much moisture.
• Geraniums do not require much fertilizer. Conduct a soil test to find out if your garden soil needs additional nutrients.
• Encourage repeat blooming by removing faded flowers and dead leaves (deadheading) from the plant.
• Reduce the potential for pests by removing plant debris from the soil surface. You can find more information on Managing insect pests on indoor plants.

Some plants like geraniums do not require a lot of nutrients to grow well and will not bloom well if over fertilized. However, if your garden soil lacks nutrients (see soil test) or if you haven’t fertilized regularly the past season, you can choose to: 

• Mix a granular fertilizer or a slow release fertilizer into the soil at planting time. Then water. Watering breaks down the solid fertilizer and makes it available for the plant to absorb.
• Or, add a water-soluble fertilizer at half-strength whenever you water your plants. These are quickly absorbed by the plant. Mix only as much as you will need each time you water.

Fertilizers are more important to plants grown in containers than those grown in garden beds as soil in containers is depleted of nutrients more quickly and must be replenished through use of fertilizers. Fertilizer is mixed into some commercial potting soil used in containers. You may find this mentioned on the product bag. 

Fertilizers are labeled with three numbers that indicate the percent nitrogen (N), phosphorus (P) and potassium (K) in the product.

• For geraniums and other annual flowers, a good option is a “balanced” fertilizer which has equal amounts of nitrogen (N), phosphorus (P) and potassium (K).
• A balanced fertilizer 10-10-10 contains 10% nitrogen, 10% phosphorus, 10% potassium). The remaining 70% of material is filler.

CAUTION: Always follow the product label instructions for mixing, rate and frequency of application.

Because they tolerate drier soil, annual geraniums are great plants for garden beds, and for outdoor containers such as window boxes, pots, and other kinds of planters which tend to dry out faster. A traditional cemetery plant, geraniums can survive and flower with minimal maintenance.

• Water when the top 1-2 inches of soil is dry.
  • Geraniums tolerate dry soil better than overly wet soil.
  • If too dry, geraniums will wilt, drop leaves and not grow well.
• Containers must have drain holes so that excess water drains out of the pot.
• Geraniums in hanging baskets require more frequent watering as they dry out quickly. Avoid hanging them in windy locations as they will dry out even faster.

You can grow geraniums in pots indoors and put them outside in late spring / early summer.

• Just move the plants indoors in their original pots.
• Dig up your plant from your garden bed or outside container, and re-pot in a clean pot, six inches wide or larger using new, sterile potting soil. Dig carefully so you don’t damage the roots.

Geraniums will most likely drop many of their leaves when brought indoors due to the change in the growing environment, but will leaf out again.

Before moving them indoors, check your plants for pests: Your Winter Garden: Pest tips for houseplants.

After moving them indoors, prune your plants to about two-thirds their size to encourage new growth.

Light

Geraniums need bright light to encourage flowering. Place plants in a sunny window with supplemental light, if needed. Southern exposure is usually the best source of light. If you don’t have a sunny window in your home, you can add supplemental lighting such as:

• A regular fluorescent tube light (sometimes called a “shop light”) hanging about 10 to 12 inches above the plants. Available at home improvement stores and hardware stores.

• An LED (light emitting diode) grow light equipped primarily with red bulbs to encourage flower buds, and blue bulbs for foliage growth. Available at garden centers, online or at specialty shops.

• Use a timer to provide supplemental light from 6 p.m. to 10 p.m. or longer if growing in a location with less natural light.

Temperature

Geraniums grow well at cooler indoor temperatures ranging from 60 to 65°F. Avoid cold, drafty areas as well as hot, dry locations. 

Watering

Indoor plants including geraniums can dry out due to our warm, dry houses.

• Always feel the plant soil before watering.
  • If the soil feels moist and cool, do not water and check back in a few days.
  • If the soil is dry to the touch, it is time to water.
• Make sure the pot drains well.
• When you water, set your plant in a sink so excess water drains out without making a mess.
• Set a saucer under your pot to protect furniture.
• Tip: If you use an unglazed clay saucer, place a coaster, trivet, etc. under it as clay can become damp and damage wood.

Fertilizing

Geraniums do not require a lot of nutrients to grow well and will not bloom well if over fertilized.

• Fertilize only when you see active growth (new leaves, buds, stems).
• Mix a water-soluble, all-purpose fertilizer at half the recommended strength with water. Apply about every three weeks during active growth.
• Never fertilize a dry, wilted plant. Water it first with plain water to moisten roots, then apply water mixed with fertilizer.

Pruning

When growing geraniums indoors, they can sometimes become “leggy”. This is caused by reduced light and creates long spaces on stems between the leaf nodes (the point where a leaf grows out from the stem). Prune or “pinch back” stems just above a leaf node to produce new growth and a plant that is stocky and well-branched.

You can keep geraniums from year to year as potted or bare root plants. Storing them in a cool basement or heated garage (about 45-50°F) works best.

Storing potted geraniums

• Move into dark storage before frost.
• Water about once a month.
• In early spring, place potted plant in a sunny window. Remove plant debris from soil, and prune off dead stems and leaves, and start watering regularly. Wait to fertilize until you see new growth.

Storing bare root geraniums

• Dig up plants the plants from your garden or containers.
• Remove excess soil from roots.
• Hang them from rafters, racks, shelves, etc. Take the plants down occasionally, place the roots in water for several hours, and hang them back up. Do this several times over the winter to prevent them from drying out completely.
• Pot your geraniums in early spring, and put them in a sunny window until danger of frost has passed.
• Note: Overwintering bare root geraniums can be challenging. Storing bare root geraniums requires a cold, damp basement or root cellar. However, it does demonstrate how tough these plants are. Experiment with several plants. Take cuttings in case you lose the original plants.

From cuttings

Sometimes a home cannot accommodate overwintering large plants due to lack of space or light. Instead of moving the whole geranium plant indoors, you can propagate new little plants for next spring by taking cuttings.

Geraniums are easy to propagate, and cuttings can be taken any time of year. Use pots or cell trays of growing medium like peat moss, sand or perlite to root your cuttings. Propagation blocks can also be purchased online and from specialty stores.  

1. Take cuttings only from healthy, disease-free plants and use a sharp pruner or knife. 

2. Dampen the growing medium with water and fill the pot/tray. Poke holes two to three inches apart or in each cell for the cuttings.

3. Cut off two to three inches of a terminal stem section (the end of a stem). 

4. Dip the cut end in water and then in root hormone powder (can be purchased at a garden center). Rooting hormone promotes fast, thick root development.

5. Gently insert the cutting in the holes, taking care not to knock off the rooting hormone powder. Roots will form at a leaf node (the leaf/stem junction), so be sure to position a node in the soil. 

6. Pat the medium in around the stems. 

7. Place in a north or east window or underneath artificial lights until rooted. This generally takes three to four weeks.

It is important not to let the cuttings dry out, so keep the growing medium moist.

• Some people use a partially open plastic bag over the container, to reduce water loss; however, this can also induce mildew and reduces air circulation.

• Check the cuttings for roots in about three weeks. Use a chopstick, pencil or popsicle stick to carefully lift, not pull, the cuttings from the medium. If more roots need to form, carefully re-plant the cutting back in the growing medium. Continue to keep the medium moist and check for roots in another week. 

After the cuttings have rooted, plant them in individual pots using sterile potting soil with an all-purpose slow release fertilizer added. Set them in a bright window. Add supplemental light at 6 inches above the plants, if needed, and keep the soil evenly moist.

From seeds

Seeds for annual geraniums can be purchased from seed companies online. Depending on the variety, geranium seed will germinate (sprout) between one to three weeks. From the time you plant the seed till you can plant outdoors is about three to four months.

1. Get an early start. Start seeds indoors in mid-January.

2. Plant seed in trays - “flats” - filled with seed starting mix. Barely cover the seed with mix.

3. Place a clear cover over the flat and locate in bright, indirect light at 75°F. You can use a heat mat to provide bottom heat or place the flat on top of the refrigerator.

4. Moisten with a spray bottle if the flat gets dry.

5. Once sprouted, move the seedlings under fluorescent lights with day temperatures in the 70s and night temperatures no lower than 60°F. Keep lights only three or four inches above the growing plants and leave them lit for 16 to 20 hours daily.

6. Start fertilizing with a liquid fertilizer at half strength.

7. Transplant into 4 inch pots when plants have three sets of leaves.

8. Continue watering and fertilizing until they are ready to be transplanted outdoors.