As a gardener, I was cultivating Amaranth 3 times in my life.
That being said, I know a lot about how long it grows, and what you need to do to properly grow this plant.
How Long Does it Take to Grow Amaranth?
Amaranth, on average, takes 90 days (3 months) to grow grains. Some varieties are grown in less than 3 months, some take even more than 4 months to grow. Usually, Amaranth leaves are ready to harvest in one month after germination occurs.
On the table below, you can see the most popular Amaranth varieties, how long they take to grow, and how big these varieties get.
| Amaranth Variety | How Long it Takes to Grow | Height |
| Caudatus ‘Coral Fountain’ | 80-120 days (2.6-4 months) | 3-5 ft (90-150 cm) |
| Caudatus ‘Dreadlocks’ | 90 days (3 months) | 2-4 ft (60-120 cm) |
| Cruentus ‘Autumn’s Touch’ | 100 days (3.3 months) | 3.5-4 ft (100-120 cm) |
| Cruentus ‘Copperhead’ | 90-120 days (3-4 months) | 4-5 ft (120-150 cm) |
| Cruentus ‘Hopi Red Dye’ | 110 days (3.6 months) | 4-6 ft (120-180 cm) |
| Cruentus ‘Hot Biscuits’ | 85 days (2.8 months) | 4 ft (120 cm) |
| Hybridus ‘Opopeo’ | 65-125 days (2.1-4.1 months) | 5-7 ft (150-210 cm) |
| Hypochondriacus ‘Pygmy Torch’ | 100 days (3.3 months) | 1-2 ft (30-60 cm) |
Amaranth can be harvested in 2 ways. First, you can harvest its leaves, and then you can harvest its grains.
Usually, leaves are harvested first. You can cut them even after one month after germination. The leaves are rich in fiber, and protein, and they can be used in soup, salad, stew or stir-fry.
After harvesting leaves, you should wait around one month to harvest grains. The grains have also culinary uses, and you can ground them into flour for bread or pasta, cook it like rice, or pop it like popcorn.
How Do You Know When to Harvest Amaranth?
There are two stages of harvesting Amaranth.
Harvesting Amaranth Leaves
If you want to know when the leaves are ready for harvesting, you have to wait at least 3 weeks after germination occurs. Then, you should observe when Amaranth develops 6-8 fully grown leaves. If the leaves are mature, you can prune and harvest them.
Harvesting Amaranth Grains
Grains will ripen many weeks before the first frost. Usually, 3 months after planting Amaranth. The best way to determine if grains are harvestable is to gently but briskly shake or rub the flower heads between your hands and see if the seeds fall readily. Birds flying around your plant may give hints as to when to start doing this.
What Factors Determine the Growth Speed of Amaranth?
Sometimes your Amaranth might take way longer to mature than expected. However, if you stick to the following rules, you might be sure, that this plant will grow properly.
Soil
Amaranth doesn’t like rich soils. If there is too much nitrogen, it might hinder flowering and seed production. Ideally, the soil pH should be 6.0-7.5. That being said, Amaranth should grow in average, or poor soil.
Watering
Amaranth doesn’t need to be watered too often. It thrives best when the soil is watered about 1 inch (16 ml) per week. It’s better to keep the soil too dry, than too wet, because it might lead to root rot, and fungal disease.
Fertilization
Fertilization is optional for Amaranth. It’s easy to overfeed this plant, and it might become leggy and less suitable for harvesting. However, when the plant is about 1 month old, you can give your Amaranth an extra boost by applying this fertilizer on Amazon.
Light
Not enough sunlight will stunt the growth of your Amaranth, and your harvesting might be delayed. Therefore, Amaranth should be located in a place where it can get at least 6 hours of sunlight per day. The warmer the climate, the less sun it generally needs.
Temperature and Humidity
If you want to harvest your Amaranth in about 3 months, the temperature should be hot, as this plant loves hot weather. Amaranth grows fastest when the temperature is 70-85 °F (21-30 °C). Heat isn’t a problem for this plant. However, if the temperature is lower than 70 °F (21 °C), for a long period of time, the harvesting might be delayed.
Spacing
Amaranth needs proper spacing to grow properly. You should keep in mind that the plants should be planted at least 15 inches (38 cm) apart to provide good air circulation, and healthy growth.
How to Harvest Amaranth?
Harvesting Amaranth leaves, and grains is different, here’s how to do it.
How to Harvest Amaranth Leaves
Amaranth leaves can be harvested by thinning and clipping. With clipping, you just need to cut or pick the green leaves from the plants using scissors or pruning shears. If you are harvesting the Amaranth leaves using thinning, you need to uproot the whole plant.
How to Harvest Amaranth Grains
To harvest Amaranth grains, cut the flowers off and place them in the bags before they turn brown. In the bags, the grains will dry. Once they are dry, shake or knock the grains loose over a cloth. At the end, rinse away the dried seed chaff.
Sources
thespruce.com, webgardner.com, towergarden.com, heirloom-organics.com