What's the correct depth for planting fall bulbs?
Written by
Michael Sullivan
Reviewed by
Prof. Samuel Fitzgerald, Ph.D.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
