Research has shown that most of alfalfa's allelopathic tendencies are autotoxic - that is, the plant exudes a chemical that reacts over time with itself, not with other plants. Continuous cropping of alfalfa results in markedly diminished yields, as accumulation of the chemical (actually 2, ethylene and medicarpin) reduces the germination and seedling development of the alfalfa itself and apprently has little or no effect on other plants. Crop rotation is SOP for alfalfa farming. Alfalfa is a very heavy nutrient drain however, and soils that have previously grown alfalfa can be deficient in both phosporous and potassium as well as of low pH. Low levels of P & K commonly produce stunting and poor growth. Testing to determine an accurate nutrient base from which to build is certainly in order. Just as an aside, although I don't have anything to support this assumption, if alfalfa's allelopathic effects were that widespread with regards to other plants, it seems unlikely that it would be so highly regarded as a soil amendment or organic nutrient source or tea base. Alfalfa does contain a natural plant growth hormone, triacontanol, that has the effect of boosting photosynthesis and increasing cell division, resulting in higher yeilds. Roses in particular respond very positively to triacontanol.

If you google "lantana allelopathy" you will find many references to this problem. Another effect is that lantana is quite a robust plant and azaleas have very shallow roots. Hence, root competition may be all that is necessary for lantana to have a detrimental effect on azaleas. Here is a link that might be useful: Some lantana is invasive in Florida.

Hi, I planted cereal rye last Fall as a cover crop. Unfortunately I don't have a plow yet to turn it in properly. The rye is now about 2". I'm wondering if I keep the rye moved can I plant vegetables and flowers in the midst? Assuming the area around them is kept free of rye and weeds. And the soil there tilled, mounded and amended with compost and 10-10-10. Soil PH is ~6.9. + I know that rye grass is slightly allelopathic, will this effect the vegetables growth adversely if grown from seed on these mounds? + Is allelopathy only in the soil or are the rye grass clippings allelopathic also? + Will allelopathy inhibit the vigorous growth of plants started in trays and transplanted on the mounds? + Will the rye grass eventually flower(and thus die) regardless of mowing? Thanks in advance! Nick

So would I . It sounds to me like this tree is just an all-round loser,unattractive, physically hurt you, and seems to poison the soil around it. Worth paying to get rid of it,roses or not. And, once it's gone, you can try "the box technique". Here in Europe we have that mysterious "rose replant disease"; I gather it is particularly bad in England. So one way to get around the problem is as follows: work the soil well, then dig a nice, big rose hole. Line the hole with cardboard,or use a cardboard box. Then you plant your rose in the box, using fresh native soil from some place that doesn't have the problem (of either the hawthorn "poison" or of having had a rose grow in it before). The idea is that the cardboard forms a barrier for a while, to allow the new rose to get started without the competition of the wierd soil; by the time it rots, the rose (hopefully) is big and established enough to duke it out on it's own. And I would probably start by trying roses that are known for vigour, that have been growing in pots for a while, so they've already got a good start.