Testing Seed Viability with the Simple Water Float Method

Starting plants from seed can be an economical way to grow flowers, herbs, and vegetables. However planting old or non-viable seeds is frustrating and wastes time and effort. Testing your seeds before planting is important to ensure success. One of the easiest methods for checking seed viability at home is the water float test.

How the Water Float Test Works

The water float test is based on the principle that viable seeds will sink in water while non-viable seeds will float. Here’s why

• Healthy seeds are denser than water due to the embryo and endosperm inside. This density causes them to sink.

• Non-viable seeds are often hollow inside. They have air pockets that make them less dense than water, so they float.

• Some seeds have impermeable seed coats that trap air inside, which also causes them to float. However, they may still germinate.

While not 100% foolproof, the float test is a good indicator of which seeds lack viability and can be culled from your stash.

Step-By-Step Float Test Instructions

Follow these simple steps to do the water float test at home:

• Fill a glass or bowl with room temperature water. Tap water is fine.

• Place a pinch of seeds (10-20) in the water. Gently stir to wet them if needed.

• Let the seeds sit for 15-20 minutes. Some may need a little longer to become fully soaked.

• Observe which seeds float to the top. Mark these as likely non-viable.

• The seeds that sink to the bottom have passed the viability test.

• Remove and dry the sunken seeds on a paper towel before planting or storing.

Tips for Improved Results

• Use fresh seeds whenever possible. Older seeds lose viability over time.

• Test seeds in small batches for easier observation.

• Try scratching impermeable seed coats with sandpaper or a file before testing. This allows water inside.

• Increase accuracy by also doing a paper towel germination test on a sample of sinking seeds.

• Some seeds with air pockets or “wings” may float at first but later sink as they absorb water. Let them sit longer.

• Agitating the water can cause viable seeds to float temporarily. Test in still water.

• Not all floaters will be non-viable. Likewise, not all sinkers will germinate well. The test isn’t 100% reliable.

When the Water Float Test Doesn’t Work

There are a few instances where the water float method may give inaccurate results:

• Mucilaginous seeds form a jelly-like coating when wet. This can make them float even if viable.

• Older seeds may have enough density to sink but not germinate well.

• Some species have naturally lightweight or buoyant seeds that will float despite high germination rates.

If in doubt, use the paper towel germination test alone or in conjunction with the float test to increase accuracy. Or just sow more seeds than needed to account for reduced viability. With experience, you’ll discover which seeds float or sink reliably in your conditions.

The simple water float test is an easy seed viability screening method to try at home before planting. While not infallible, it can help highlight seeds that likely won’t germinate, saving time and frustration later. Use it as a helpful guide, not an absolute rule, for seed starting success.

Frequency of Entities:
seeds – 28
water – 12
float – 10
viable/viability – 9
sink – 7
germinate/germination – 5
non-viable – 3
seed coat – 2
mucilaginous – 1