The depth for planting bulbs will decide if they flourish, or wither away. To determine the planting depth, I use the three-times-height rule. This means that for a 3-inch daffodil, I would plant it 9 inches deep. I have learned this through experience and testing several times. A great story, in this vein, is about a client who promptly asked me to plant crocus 2 inches deep in clay. I did not think to question him; but, by February the frost heave had pushed the crocus up, like mini-icebergs.
Large Bulbs (Tulips/Daffodils)
- 8-10 inches deep in zones 3-5
- 6-8 inches in zones 6-7
- Add 2 inches depth for sandy soils
- Reduce 1 inch depth in heavy clay
Small Bulbs (Crocus/Snowdrops)
- 3-4 inches deep standard
- 5 inches in windy, exposed areas
- Shallow 2-inch depth for container planting
- Cluster 10+ bulbs per square foot
The soil type is a game changer. For us sandy soils, I add 1 inch to the recommended depths. That counters frost penetration. For clay soils, I subtract 1 inch to prevent rot. A gardener from Wisconsin increased the return of tulips by planting them 8 inches deep instead of 10 inches in her loamy soil.
Northern Zones (3-5)
- Add 2 inches depth for wind protection
- Bury bulbs below frost line (varies by county)
- Use late-blooming varieties for freeze resistance
- Mulch with 6 inches straw post-planting
Southern Zones (8-10)
- Reduce depth by 25% for heat regulation
- Pre-chill bulbs 12 weeks in refrigeration
- Plant in November-January window
- Water monthly if winter droughts occur
It is advisable to measure from the bottom base of the bulb- not from the surface of the soil. I utilize a depth stick that is marked in inches. When planting in mass, how deep the trench is focused, rather than individual holes. One of my client's 500-bulb display projects was highly successful in her very laser-leveled 8-inch trench before placing her bulbs.
Read the full article: 7 Essential Tips to Plant Bulbs This Fall
