Variegated Allamanda, Allamanda cathartica (Yellow) - Plant

Allamanda plant is grown by seeds and cuttings. Consider the following points to grow a plant. 
1. Sunlight- 4-6 hours of direct bright sunlight is required. 
2. Soil- Soil or potting mixture should be well-drained, fertile and nutrient-rich.
3. Water-Water the plant when 1-2 inch surface soil layer feels dry to touch. 
4. Fertilizer - Apply any organic fertilizer during the main growing Spring season(February-March).

Note - For further details check the product description on nurserylive.com 

Prune your plant in the month of December-January, These shrubs grow quite quickly and without proper pruning, Allamanda rapidly become overgrown and look bulky. Cut out all damaged, dead or dying branches. Prune out any stems that rub against or cross another stem. Prune Allamanda shrubs about once a month throughout the growing season to keep them looking tidy. Prune lightly, however, because a hard pruning can result in few new flowers and very dense foliage.

Yes, Allamanda plant is poisonous if digested.

Yes, all Allamanda plants are perennial.

You can plant an Allamanda outdoor where 4-6 hrs. of direct bright sunlight is available.

Consider the following points to grow Allamanda plant from cuttings
1. Take pencil size thick cutting of well mature stem to a length of 3 inches (
7.5 cm.) long and has several leaves. Remove the bottom 1 inch (
2.5 cm.) of leaves.
2. Then dip the bottom of the cutting in rooting hormone, and place the 3/4 portion cutting into a small container with well-draining soil and water the cuttings.
3. Rooting will start within 1-2 weeks.

Note - For further details check the product description on nurserylive.com

You can propagate Allamanda plant from cuttings and seeds.

It is maybe due to Insufficient light, less or overwatering. So make sure your plant is getting enough amount of bright sunlight(4-6 hrs), water it when the upper layer of the soil(1-2 inches) feels dry to touch. Check the moisture in the soil before watering it, Poke your finger into the soil, if dry then apply water. Do not overwater the plant. This plant doesn’t like to sit in waterlogged soil, so drainage is important to prevent rot. Check the drainage hole to allow excess water to escape. Protect your plant from a cold climate by keeping it in a mildly warm and dry location. Feed it with any organic nitrogen-rich fertilizer once a month.

You can plant Allamanda seeds in the pot as well as in-ground.To plant Allamanda seed consider the following points
1. Use a pot having 7 inch upper diameter and drainage holes.
2. Fill the pot with well-drained soil. To sow seeds make a hole about 1 inch in soil, place seeds in it, cover with soil and apply water.
3. Maintain the moisture in soil by applying water if soil in pot (1-2 inch) feels dry to touch.
4. Keep the pot at a location receiving indirect bright light. Seeds will germinate within a week.

Note - For further details check the product description on nurserylive.com

Consider the following points to care for Allamanda plant
1. Sunlight- 4-6 hours of natural direct bright sunlight is required. 
2. Soil- Soil or potting mixture should be well-drained, fertile and nutrient-rich.
3. Water-Water the plant when 1-2 inch surface soil layer feels dry to touch. 
4. Fertilizer - Apply any organic fertilizer once a month.
5. Repot - When plant overgrows in the current pot or after every 2 -3 years change the pot. 

Allamanda will grow up to 10-20 ft. tall