With root establishment being the main goal after planting, here are some key things you can do to further encourage root growth. Plant at the correct depth, keep the soil moist but not too wet, avoid nitrogen fertilizer, correctly stake larger trees, and apply mulch after planting.
Planting a tree too deep can kill the tree or result in the tree being stressed throughout its life; hence being more susceptible to pest problems. A tree is planted at the correct depth if you can see the trunk taper, also known as root flare, just above the soil line or if the first lateral root is just below the soil line.
Too deep of planting kills roots and slows root growth due to a lack of soil oxygen. Because plant roots need oxygen to grow and function, overwatering also kills roots and reduces new root growth. Moisture is just as important to root growth as oxygen. This is why we recommend keeping the soil moist, but not saturated. Be sure to moisten the soil beyond the planting hole.
New trees are often killed by too wet of soils. This may be due to overwatering or to heavy clay soils that do not drain well. Always check the soil to be sure it needs water before irrigating; especially if the tree is hit by lawn irrigation. Digging the hole about one foot wider than the root ball can improve water drainage by loosening surrounding soil.
Nitrogen fertilizer is best avoided at planting time as it can promote stem and leaf growth as the expense of roots. Nitrogen is helpful if a soil is low in nitrogen; however, most Nebraska soils are fertile enough to support tree growth during the first year. If a tree is being planted into or near a lawn, it will receive plenty of nitrogen from lawn fertilization throughout its life.
Most Nebraska soils are also high in phosphorous and the addition of this nutrient is not needed, especially during fall when warmer soil temperatures make it easier for roots to take up phosphorous. The addition of phosphorous may be beneficial during spring planting due to cold, wet soils.
Staking of larger trees after planting is done to keep the root ball from shifting and tearing young roots. Correct staking involves placing the staking material as low on the tree as possible. It’s okay if the top half of the tree moves with the wind as long as the root ball is not shifting in the soil. Use staking materials that will not damage or girdle the trunk and stake for one year only.
Research has shown trees establish almost twice as fast if mulched. Mulch maintains a cool, moist soil which promotes root growth. Mulch also keeps the tree from having to compete with turfgrass and weeds and prevents trunk injury from mowers and weed trimmers.
Mulching properly is just as important as proper staking, watering and fertilization. Place a two to four inch layer of organic mulch in at least a four foot diameter ring around the tree. Place the mulch about one foot away from the tree trunk to avoid moisture being held against the trunk or voles hiding in the mulch and gnawing on tree trunks during winter.
Source: Kelly Feehan, Educator, Platte County
Ann Fenton
Extension Educator, Pierce County
